Explanation:

The correct answer is D. The classification of testicular tumors is based on cell of origin. Germ cell tumors originate from the cell line maturing into sperm cells. Non-germ cell tumors originate from Sertoli cells, Leydig cells, and fibroblasts. Germ cell tumors represent 95% of all testicular neoplasms. To simplify, approximately one third are seminomas, one third are nonseminomatous germ-cell tumors (NSGCT), and one third are mixed tumors, ie, tumors that include seminomatous and nonseminomatous differentiation. The age, mode of presentation, and histologic features of this clinical case are classic for seminoma. This neoplasm consists of two cell types: neoplastic cells (prominent nucleoli and clear cytoplasm) and accompanying lymphocytes. These tumors are very radiosensitive and have a better prognosis than nonseminomas.

The following are all NSGCT:

- Choriocarcinoma (choice A) recapitulates chorionic villus differentiation and expresses human chorionic gonadotropin (hCG). This tumor is identical to choriocarcinoma, arising in the placental tissue or ovaries.

- Embryonal cell carcinoma (choice B) is very undifferentiated and consists of epithelial cells arranged in a tubular or glandular pattern.

- Teratoma (choice F) contains tissue and organoid components deriving from more than one germ layer. For example, a teratoma may contain ectodermal derivatives (skin, hair, teeth, and neural tissue), mesodermal derivatives (muscle, connective tissue, cartilage, and bone), and endodermal derivatives (respiratory and digestive epithelium).

- Yolk sac tumor (choice G) differentiates along the yolk sac line. It is the most common testicular tumor in infancy and early childhood. Expression of α-fetoprotein (AFP) is characteristic.

Leydig cell tumors (choice C) and Sertoli cell tumors (choice E) are non-germ cell tumors. These neoplasms originate from Leydig cells and Sertoli cells, respectively. Both of these may elaborate androgens and/or estrogens and occasionally manifest with sexual precocity in children and masculinization or feminization in adults.

Two weeks after birth, a neonate develops sepsis, skin vesicles, and conjunctivitis. Over the next several days, the baby's condition deteriorates with development of seizures, cranial nerve palsies, and lethargy. The baby dies approximately one week after onset of symptoms. Which of the following infectious agents would most likely cause this clinical presentation?     A. Cytomegalovirus     B. Herpes simplex     C. Rubella     D. Syphilis     E. Toxoplasmosis

Explanation:

The correct answer is B. All of the agents listed, including choices A, C, D and E, can cause devastating congenital infections with high mortality and often with major organ malformation (the TORCH agents: Toxoplasma, other, rubella, cytomegalovirus, herpes simplex). However, it is herpes simplex type II, typically acquired during delivery, that causes the devastating neonatal encephalitis described in the question stem. The mortality rate for neonatal herpes is about 65%, and only 10% of the babies escape without neurologic sequelae. A point worth remembering is that adult herpes encephalitis (in non-immunosuppressed individuals) is usually due to herpes simplex I, while neonatal and congenital herpes are usually due to herpes simplex II.

A 57-year-old man presents with an enlarged right inguinal lymph node on the medial side of the horizontal chain. Biopsy demonstrates a well-differentiated adenocarcinoma forming large glands and producing copious amounts of mucin. Which of the following is the most likely primary site for this cancer?     A. Anorectal region     B. Ascending colon     C. Duodenum     D. Stomach     E. Transverse colon

Explanation:

The correct answer is A. The lymph nodes of the groin are divided into superficial and deep groups. The superficial group is further divided into horizontal and vertical chains. It is worth remembering that tumors from the penis, vagina, and anal canal can drain to the medial side of the horizontal chain of the superficial group of inguinal lymph nodes.

Tumors from the ascending colon (choice B) do not usually metastasize early to easily palpable lymph nodes.

Tumors from the duodenum (choice C) do not usually metastasize early to easily palpable lymph nodes.

Tumors from the stomach (choice D) can metastasize early to the easily palpable left supraclavicular nodes (also called Virchow's nodes or sentinel nodes).

Tumors from the transverse colon (choice E) do not usually metastasize early to easily palpable lymph nodes.

A 45-year-old female homemaker presents to her physician because of headaches followed by "visual problems." Neurological examination reveals no impairment of higher cortical functions. Sense of smell is preserved, but the patient has bilateral

papilledema and bitemporal hemianopia. The other cranial nerves are normal. There is no evidence of motor or sensory impairment, and Babinski's sign is absent. Pituitary adenoma is confirmed on MRI, and a hypophysectomy is scheduled. The tumor will be approached transnasally, through the     A. cavernous sinus     B. ethmoid sinus     C. frontal sinus     D. mastoid sinus     E. sphenoid sinus

Explanation:

The correct answer is E. The hypophysis is approached transnasally through the sphenoid sinus.

Inadvertent transgression into the cavernous sinus (choice A) would lead to torrential venous or arterial hemorrhage from the cavernous sinus itself or the internal carotid artery contained within.

The ethmoid sinus (choice B) is related to the medial wall of the orbit.

The frontal lobe lies behind the frontal sinus (choice C).

The mastoid sinus lies (choice D) within the temporal bone and communicates with the middle ear.

A 65-year-old man develops a vesicular rash localized to a narrow circumferential band on one side of his chest. The rash is very painful, and the vesicles are confluent with some ulceration. No other significant findings are demonstrated on physical examination. Which of the following diagnoses is most likely to be correct?     A. Chicken pox     B. Herpes simplex I infection     C. Herpes simplex II infection     D. Measles     E. Shingles

Explanation:

The correct answer is E. This is shingles, the recurrent form of herpes zoster infection, which is usually (except in the case of immunosuppressed patients) confined to a single dermatome. Isolated vesicles may be seen outside the dermatome. The primary herpes zoster infection precedes the development of shingles by years or decades; the prevalence of shingles rises steadily with age, to the point that 1% of people older than 80 years have the condition. Shingles lesions are infections and should be considered an infectious

hazard in the hospital setting. Acyclovir can ameliorate the condition.

Varicella, or chicken pox (choice A), is the primary form of herpes zoster infection and affects face and trunk diffusely.

Herpes simplex I (choice B) affects oral and perioral sites.

Herpes simplex II (choice C) primarily affects genital sites.

Measles (choice D) causes a blotchy rash, rather than a dermatomal one.

A 40-year-old woman has had several episodes of rheumatic fever as a child. She is currently afebrile and feels well, and has come to a hospital for monitoring echocardiography. Which of the following would be most likely to be seen in this patient's mitral valve?     A. Ballooning of valve leaflets     B. "Fish mouth" valve     C. Irregular beads of calcification in annulus     D. Large bulky vegetation with adjacent leaflet perforation     E. Tiny vegetations along line of closure of valve leaflet

Explanation:

The correct answer is B. Acute rheumatic fever is a multisystem inflammatory disease that can follow group A streptococcal pharyngitis. The heart is a primary target of this disease and may be damaged sufficiently to develop permanent sequelae. The most important of these sequelae is chronic rheumatic heart disease with valvular damage. The damage most often involves the mitral and/or aortic valves. The resulting thickened, blunted cardiac valve leaflets, often with fibrous bridging between valve leaflets and calcification, frequently take on a "fish mouth" or "button hole" stenotic morphology.

Associate ballooning of valve leaflets (choice A) with mitral valve prolapse.

Associate irregular, beadlike calcifications on the annulus (choice C) with calcification of the mitral annulus, seen in elderly individuals.

Associate large vegetations and leaflet perforation (choice D) with acute bacterial endocarditis, which usually involves healthy, rather than previously damaged, valves.

Associate tiny vegetations along line of closure (choice E) with marantic (nonbacterial thrombotic) endocarditis, most typically seen at autopsy of patients who died after protracted illness.

A 65-year-old man consults a physician because he has had severe alternating

constipation and diarrhea for the past two months. Hemoccult test on a stool sample is positive for occult blood. Colonoscopy demonstrates a large napkin-ring mass 25 cm above the anal verge, in the descending colon. To which of the following nodes would this tumor be most likely to first metastasize?     A. Gastroepiploic     B. Inferior mesenteric     C. Internal iliac     D. Subpyloric     E. Superficial inguinal

Explanation:

The correct answer is B. This person most likely has an invasive adenocarcinoma of the colon involving the descending colon, but above the rectum. The rich lymphatics of the descending colon drain through the mesentery to the inferior mesenteric nodes before draining to the lymphatics and nodes along the aorta.

The gastroepiploic nodes (choice A) drain the greater curvature of the stomach.

The internal iliac nodes (choice C) drain the bladder and male internal genitalia.

The subpyloric nodes (choice D) drain the distal stomach, pancreas, and duodenum.

The superficial inguinal nodes (choice E) drain the rectum, vagina, and perineum.

CT scan of the head of a mentally retarded child with seizures demonstrates multiple "tubers" of the brain. The child also has adenoma sebaceous skin lesions. Which of the following lesions is associated with this patient's disease?     A. Cardiac rhabdomyomas     B. Cerebellar angiomas     C. Leptomeningeal angiomatosis     D. Port-wine nevus     E. Retinal angiomatosis

Explanation:

The correct answer is A. The disease is tuberous sclerosis, which is one of the slowly progressive, familial, neurocutaneous disorders known as phacomatoses. The tubers in the brain are composed of haphazardly oriented, bizarre neurons and astrocytes in a markedly gliotic background. These hamartomatous lesions are associated with hamartomatous lesions at other sites, including adenoma sebaceum of the skin, pancreatic cysts, renal angiomyolipomas, and cardiac rhabdomyomas. The cardiac rhabdomyomas are important to suspect clinically because they can cause a ball valve-like cardiac lesion that intermittently impairs blood circulation.

Associate cerebellar angiomas (choice B) with von Hippel-Lindau syndrome.

Associate leptomeningeal angiomatosis (choice C) with Sturge-Weber disease.

Associate port-wine nevus (choice D) with Sturge-Weber disease.

Associate retinal angiomatosis (choice E) with von Hippel-Lindau syndrome.

One of three blood culture bottles drawn from a patient with unexplained fevers reveals gram-positive cocci growing in clusters. Which of the following tests would be most useful in determining whether this organism is a part of the normal skin flora?     A. Bacitracin resistance     B. Catalase     C. Coagulase     D. Novobiocin resistance     E. Optochin resistance

Explanation:

The correct answer is C. Gram-positive cocci in clusters are staphylococci. Staphylococcus aureus is a common pathogen that should not be considered normal skin flora. Other staphylococci, especially Staphylococcus epidermidis, may contaminate blood cultures and can be differentiated from Staphylococcus aureus by the coagulase test. S. aureus is the only coagulase-positive staphylococcus.

Bacitracin sensitivity differentiates Streptococcus pyogenes from the other beta-hemolytic streptococci, which are bacitracin resistant (choice A).

The catalase test (choice B) is used to differentiate streptococci from staphylococci. Staphylococci produce catalase and can generate oxygen bubbles in hydrogen peroxide, whereas streptococci cannot.

Novobiocin resistance (choice D) differentiates the coagulase-negative staphylococci into S. epidermidis (novobiocin sensitive) and S. saprophyticus (novobiocin resistant).

Optochin resistance (choice E) differentiates the major pathogenic alpha-hemolytic streptococci. S. pneumoniae is optochin- and bile-sensitive whereas S. viridans is resistant to both optochin and bile.

A diabetic mother gives birth to a baby who dies in the first week of life. Autopsy reveals a severe cardiac malformation. Which of the following is the most likely diagnosis?     A. Atrial septal defect     B. Coarctation of the aorta     C. Eisenmenger's syndrome

     D. Tetralogy of Fallot     E. Transposition of the great arteries

Explanation:

The correct answer is E. Maternal diabetes is best known for causing large but immature-for-age babies. There is also a specific association between maternal diabetes and transposition of the great vessels. In transposition of the great vessels, the aorta takes off from the anterior part of the right ventricle and the pulmonary trunk takes off from the posterior part of the left ventricle. This produces a complete separation of the systemic and pulmonary circulations. Without surgical correction, most affected infants die within the first months of life, although a patent ductus arteriosus, patent foramen ovale, or ventricular septal defect may allow enough mixing of blood to temporarily sustain life.

In atrial septal defect (choice A) blood can pass from one atrium to the other.

Associate coarctation of the aorta (choice B) with Turner syndrome.

Eisenmenger's syndrome (choice C) is a shift from a left-to-right shunt to a right-to-left shunt secondary to developing pulmonary hypertension.

Tetralogy of Fallot (choice D) consists of a ventricular septal defect, an overriding aorta, pulmonic stenosis, and right ventricular hypertrophy. It is the most common cause of early cyanosis.

A patient has a large meningioma involving the parasagittal region and falx cerebri. Which of the following neurologic deficits would this mass lesion be expected to produce?     A. Altered taste     B. Leg paralysis     C. Loss of facial sensation     D. Ptosis     E. Unilateral deafness

Explanation:

The correct answer is B. A meningioma of the parasagittal region and the falx cerebri would be located superiorly, between the two hemispheres. In this position, it could compress the sensory (postcentral gyrus) or motor cortex (precentral gyrus) supplying the lower extremities.

Taste (choice A) is supplied by cranial nerves VII, IX, and X. These nerves arise in the brainstem.

Facial sensation (choice C) is supplied by cranial nerve V, the nuclei of which are in the

brainstem.

Ptosis (choice D) can be caused by a deficit in cranial nerve III, which arises from the brainstem.

Unilateral deafness (choice E) suggests damage to cranial nerve VIII, which arises from the brainstem.

A 28-year-old man comes to his physician complaining of heartburn for one week. After a short trial with antacids, which did not provide significant relief, the patient undergoes endoscopic studies. These reveal punched out ulcers in the lower segment of the esophagus, similar to those shown in the picture. Biopsies from these areas demonstrate chronic inflammation and epithelial cells with glassy intranuclear inclusions. Which of the following is the most likely cause of this condition?     A. Candida albicans     B. Chemical injury     C. Helicobacter pylori     D. Herpes simplex virus     E. Reflux esophagitis

Explanation:

The correct answer is D. Herpes simplex is one of the most common etiologic agents of infective esophagitis. The disease may manifest in immunocompetent hosts, although it is more frequent in immunocompromised (e.g., AIDS) patients. Punched out ulcers, such as the ones in the gross picture, are highly characteristic. The histology is rather nonspecific (chronic inflammatory infiltrate), except for the presence of glassy intranuclear eosinophilic inclusions. Cytomegalovirus is the other common viral etiology of esophagitis. This form would be characterized by purple intranuclear inclusions combined

with granular cytoplasmic inclusions, and markedly enlarged cell size.

Candida albicans(choice A) gives rise to esophagitis in immunocompromised hosts or develops superimposed on CMV/herpes ulcers. Candida organisms are easily identified admixed with squamous cells and neutrophils.

Chemical injury (choice B) is usually due to accidental or suicidal ingestion of corrosive agents, such as lye, acids, and detergents. The mucosa shows diffuse erythema, edema, and (in severe cases) extensive ulcerations.

Helicobacter pylori(choice C) does not cause esophagitis. This gram-negative organism is associated with chronic gastritis of the antrum, peptic ulcer, gastric adenocarcinoma and lymphoma.

Reflux esophagitis (choice E) is the most common form of esophagitis. It is due to reflux of acid contents from the stomach. Erythema and edema are seen in the lower esophageal portion, often associated with intestinal metaplasia (Barrett esophagus).

During a barroom fight, a 24-year-old man is hit with a bottle on the lateral aspect of the lower leg. The man receives a deep laceration about halfway down his lower leg, in the vicinity of the fibula. Following the injury, he loses sensation over most of the dorsum of the foot. Which of the following muscles is also innervated by the nerve that was likely damaged?     A. Extensor digitorum brevis     B. Extensor digitorum longus     C. Extensor hallucis longus     D. Peroneus longus     E. Peroneus tertius

Explanation:

The correct answer is D. The nerve in question is the superficial peroneal nerve (also called the musculocutaneous nerve), which innervates much of the skin of the dorsum of the foot (except for the first web space innervated by the deep peroneal nerve, and the medial and lateral borders of the foot innervated by the saphenous and sural nerves, respectively). The superficial peroneal nerve is a branch of the common peroneal nerve, and also innervates the peroneus longus and peroneus brevis muscles.

All of the other muscles (choices A, B, C, and E) are innervated by the deep peroneal nerve.

A 56-year-old woman develops a global amnesia with a profound loss of ability to remember any new information and retrograde amnesia stretching back about 3 months. The patient remains conscious and is able to drive to an emergency room, although she

seems disoriented and keeps repeating the same questions that have just been asked. After a few hours, her memory completely returns and she is apparently normal, but does not remember the attack. Episodes of this type suggest which of the following?     A. Glioblastoma multiforme     B. Meningioma     C. Stroke     D. Transient ischemic attack     E. Viral meningitis

Explanation:

The correct answer is D. Transient global amnesia, such as that observed in this patient, is a very well documented, although rare, condition that is thought to usually represent a variant of a transient ischemic attack (TIA). TIAs in the posterior cerebral territory are thought to be involved in the pathogenesis of these events. Migraine and epileptic attacks have also been implicated in some cases of transient global amnesia. In most patients, the attacks do not recur.

Tumors (choices A and B) and strokes (choice C) affecting the hippocampus can potentially cause memory loss, but the symptoms would not be transient and multiple other neurologic findings would typically also be seen.

Viral meningitis (choice E) does not usually cause amnesia.

A 7-year-old girl develops a fever, conjunctivitis, photophobia, and a cough. Her pediatrician notes white spots on a bright red background on the girl's buccal mucosa. Within days, a rash begins around the hairline, then spreads to the trunk and extremities. One week later, the child suddenly begins to convulse, and loses consciousness. She is taken to the emergency room, where involuntary movements and pupillary abnormalities are noted. Which of the following would most likely be seen on CNS biopsy?

   A. Demyelination of white matter of cerebral hemispheres with abnormal giant oligodendrocytes

    B. Perivenous microglial encephalitis with demyelination    C. Phagocytosis of motor neurons in the spinal cord

   D. Severe hemorrhagic and necrotizing encephalitis of the temporal lobe with eosinophilic Cowdry type A inclusion in neurons and glia

    E. Small granulomas with central caseation in the meninges

Explanation:

The correct answer is B. The initial history given is classic for measles, with the appearance of Koplik's spots (white spots on the buccal mucosa) followed by a rash beginning along the neck and hairline and spreading to the trunk and extremities. The sequela this child is experiencing is post-infectious encephalomyelitis, which can follow either infection with measles, varicella, rubella, mumps, or influenza, or vaccination with

vaccinia vaccine or rabies vaccine derived from nervous tissue. Treatment is supportive, with a mortality of 15 to 40%; survivors frequently have significant permanent neurologic deficits. The pathologic finding is perivenous microglial involvement with demyelination.

Choice A describes the findings of progressive multifocal leukoencephalopathy, a demyelinating disease caused by infection with JC virus, especially in immunocompromised individuals.

Choice C describes the findings of poliomyelitis, a paralytic disease affecting the ventral horn of the spinal cord and motor cortex, caused by an enterovirus (poliovirus).

Choice D describes the findings in herpes encephalitis, which typically affects the inferomedial temporal lobes and orbitofrontal gyri.

Choice E describes the findings in tuberculous meningitis, caused by M. tuberculosis.

Aortic angiographic studies are performed on a 20-year-old man because of progressive left ventricular failure and abnormal echocardiographic findings suggestive of valvular disease. The picture shows his aortic angiogram. If this patient had functional insufficiency of the valve shown by the arrows, which of the following abnormal sounds would be heard on chest auscultation?     A. Continuous systolic-diastolic murmur     B. Diastolic murmur in the precordium

     C. Friction rub     D. Midsystolic click followed by murmur     E. Systolic murmur radiating to the neck

Explanation:

The correct answer is B. This angiogram demonstrates the aorta, from its origin to the thoracic segment. The main aortic branches arising from the aortic arch are visualized as well, including (in a proximal-distal direction) the brachiocephalic trunk, left common carotid, and left subclavian. The lateral swellings indicated by the arrows correspond to the cusps of the aortic valve. If the aortic valve is insufficient, the blood flows back from the aorta into the left ventricle during diastole, a pathophysiologic phenomenon described as aortic regurgitation. Aortic regurgitation creates turbulent blood flow, which results in a diastolic murmur. This murmur is most intense in the precordium and usually lasts for the whole diastole.

A continuous systolic-diastolic murmur (choice A) is highly characteristic of patent ductus arteriosus. Abnormal persistence of a patent ductus arteriosus into adulthood allows constant shunting of blood from a high-pressure system (aorta) to a low-pressure system (pulmonary artery), thus resulting in a continuous, systolic-diastolic murmur.

The designation of friction rub (choice C) suggests its origin. This auscultatory abnormality is a rubbing sound arising from friction of the parietal and visceral leaflets of a serosal membrane. Friction rubs are associated with inflammatory processes involving the pericardium or pleura, which result in accumulation of fibrin-rich exudate on the visceral surface.

A midsystolic click followed by murmur (choice D) is due to mitral valve prolapse, a common (but usually asymptomatic) abnormality of the mitral valve. Myxomatous degeneration of the mitral leaflets is the underlying organic alteration, which leads to a "floppy" mitral valve. This floppy valve prolapses into the left atrium during systolic contraction, resulting in the characteristic click. If regurgitation is also present, the click is followed by a murmur.

A systolic murmur radiating to the neck (choice E) may result from stenosis of the aortic valve. This is usually caused by calcification of the aortic cusps, which produces a narrowed ostium. The resulting murmur radiates to the neck as the wave sound is transported along the direction of blood flow.

An unrestrained driver sustains a blunt chest injury in an automobile accident, and is taken to the emergency room. The emergency room physician wants to determine if the heart was bruised when he collided with the steering wheel. The levels of which of the following creatine kinase isoenzymes or combinations of creatine kinase isoenzymes would be most useful for this determination?     A. BB isoenzyme     B. MB isoenzyme of creatine kinase

     C. MM isoenzyme of creatine kinase     D. Total creatine kinase and the MB isoenzyme     E. Total creatine kinase and the MM isoenzyme

Explanation:

The correct answer is D. The MB isoenzyme of creatine kinase is associated with heart damage; the MM isoenzyme is associated with muscle damage; and the BB isoenzyme is associated with brain damage. Actually, most tissues contain a mix of creatine kinase isoenzymes, but one species often predominates. In the case of myocardial infarction not occurring in the setting of trauma, either total creatine kinase, or, preferentially, the MB isoenzyme can be used for monitoring. However, in a complex setting such as in this case, where there is known skeletal muscle damage secondary to trauma, the ratio of the MB isoenzyme to total creatine kinase is most informative.

A 28-year-old female complains to her doctor that she is in danger of losing her job. She states that she is late to work almost everyday because, before she leaves for work, she must check all of the faucets to make sure the water is turned off. She also needs to repeatedly check to make sure that her stove is off. When she is finally ready to leave, she returns from her car several times to ensure that her doors and windows are locked. Which of the following drugs will her physician most likely prescribe?     A. Buspirone     B. Chlorpromazine     C. Clomipramine     D. Imipramine     E. Phenelzine     F. Zolpidem

Explanation:

The correct answer is C. This patient is suffering from obsessive-compulsive disorder. Clomipramine, a tricyclic antidepressant, and the selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, are effective in this disorder. None of the other answer choices listed constitute effective therapy for this disorder.

Buspirone (choice A) is a non-benzodiazepine anxiolytic that does not have marked sedative or euphoric effects. Unlike the benzodiazepines, buspirone is devoid of hypnotic, anticonvulsant, and muscle relaxant properties.

Chlorpromazine (choice B) is an antipsychotic (phenothiazine) drug.

Imipramine (choice D) is a tricyclic antidepressant.

Phenelzine (choice E) is a monoamine oxidase inhibitor type of antidepressant.

Zolpidem (choice F) is a non-benzodiazepine hypnotic agent.

A patient develops an excruciatingly painful infection of the anterior half of the external ear canal. Which of the following nerves transmits this impulse?     A. Auricular branch of the vagus     B. Auriculotemporal nerve     C. Greater auricular nerve     D. Lesser occipital nerve     E. Vestibulocochlear nerve

Explanation:

The correct answer is B. The ear has a complex sensory nerve supply, which includes all of the nerves listed. A consequence of this complexity is that pain actually originating in other sites (teeth and sinuses are notorious) may be misinterpreted as ear pain or (less commonly) pain originating in the ear may be misinterpreted as arising from other sites. The anterior half of the external ear canal is supplied by the auriculotemporal nerve, which also supplies the facial surface of the upper part of the auricle.

The auricular branch of the vagus (choice A) supplies the posterior half of the external ear canal.

The greater auricular nerve (choice C) supplies both surfaces of the lower part of the auricle.

The lesser occipital nerve (choice D) supplies the cranial surface of the upper part of the auricle.

The vestibulocochlear nerve (choice E) supplies hearing and motion sense.

A 24-year-old woman vacationing for the summer on Cape Cod reports to a general practitioner complaining of low-grade fever, headache, fatigue, and malaise. The physician observes an extensive skin rash on her arm (see photograph above). To which of the following groups of organisms does the causative agent belong?     A. Prokaryotes lacking a cell wall     B. Prokaryotes with axial filaments     C. Prokaryotes with cell wall lacking muramic acid     D. Prokaryotes with normal cell wall but inadequate ATP     E. Prokaryotes with sterols in their membrane

Explanation:

The correct answer is B. The patient has Lyme Disease, as evidenced by the pathognomonic skin lesion, erythema (chronicum) migrans, a migrating red rash resembling a bull's eye. The other useful clues are the geographic location (home of the vector tick, Ixodes), the symptoms, and the summer timing, coinciding with the possible exposure to the tick vector. This disease is caused by a large spirochete, Borrelia burgdorferi, a prokaryote that is motile by means of axial filaments.

Prokaryotes lacking a cell wall (choice A) describes the characteristics of the genus Mycoplasma and its relatives, and there are no mycoplasmal diseases that share this set of symptoms.

Chlamydia are prokaryotes with cell walls lacking muramic acid (choice C). Chlamydial organisms are intracellular pathogens involved in sexually transmitted diseases and blindness.

Rickettsia are prokaryotes with normal cell walls, but inadequate ATP (choice D). These organisms are well known for causing very distinctive rashes, and are arthropod-borne, but the rashes caused by these organisms do not resemble that shown.

Prokaryotes with sterols in their membrane (choice E) describes the characteristics of the genus Mycoplasma and its relatives. There are no mycoplasmal diseases that present as described above.

A patient comes to medical attention because of a kidney stone. During the clinical evaluation, the patient reveals that he has had a history of stomach ulcers. Which of the following diagnoses should the physician consider?     A. Horner syndrome     B. Shy-Drager syndrome     C. Sipple syndrome     D. Turcot syndrome     E. Wermer syndrome

Explanation:

The correct answer is E. This patient may have Wermer syndrome (multiple endocrine neoplasia type I; MEN type I). In this disorder: 1) parathyroid hyperplasia or adenomas can cause hypercalcemia and kidney stones; 2) pancreatic neoplasms may secrete any of the islet hormones or may secrete gastrin, producing Zollinger-Ellison syndrome with multiple peptic ulcers; and 3) pituitary adenomas may occur rarely.

Horner's syndrome (choice A) is characterized by ptosis, miosis, and in many cases, hemianhidrosis. It is usually related to involvement of the cervical sympathetic plexus by tumor (usually lung cancer).

In Shy-Drager syndrome (choice B), there is autonomic nervous system failure, leading to orthostatic hypotension and parkinsonism.

Sipple syndrome (choice C) is MEN type II, characterized by medullary thyroid carcinoma, pheochromocytoma, and parathyroid disease.

In the very rare Turcot syndrome (choice D), adenomas of the digestive tract and central nervous system gliomas (astrocytoma and medulloblastoma) occur.

Before being approved by the FDA, a chemical is tested for carcinogenicity by examining its mutagenic effects on bacterial cells in culture. Which of the following tests is used to make this determination?     A. Ames test     B. Nitroblue tetrazolium test     C. Watson-Schwartz test     D. Widal test     E. Woellner enzyme test

Explanation:

The correct answer is A. The test described is the Ames test, which measures damage to DNA and correlates well with carcinogenicity in vitro. It is relatively inexpensive to perform, compared to other tests of carcinogenicity, and is frequently used as a screening test for potential carcinogens.

The nitroblue tetrazolium test (choice B) is used to examine the ability of neutrophils to undergo a respiratory burst, and is used in the diagnosis of hereditary immunodeficiencies.

The Watson-Schwartz test (choice C) detects porphobilinogen in urine, and is used in the diagnosis of porphyrias.

The Widal test (choice D) is used to diagnose typhoid fever.

The Woellner enzyme test (choice E) detects heterophil antibodies in patients with Epstein-Barr virus infection, such as infectious mononucleosis.

A 10-year-old boy is in a fire and sustains burns over 25% of his body. The next day, his serum urea nitrogen (BUN) is 30 mg/dL and his serum creatinine is 0.8 mg/dL. He receives intravenous fluids throughout his course and never has a significant drop in blood pressure or urine output. Which of the following most likely accounts for his BUN and creatinine values?     A. Decreased renal perfusion     B. Distal urinary tract obstruction     C. Increased synthesis of urea     D. Renal glomerular disease     E. Renal tubule interstitial disease

Explanation:

The correct answer is C. This patient has elevated BUN and normal serum creatinine. Raised BUN with normal creatinine can be seen in prerenal causes of azotemia, which can be subclassified into those due to decreased perfusion of the kidney and those due to increased synthesis of urea. In this case, the boy's blood pressure and urine output were maintained, so inadequate renal perfusion is unlikely. The burns themselves can cause significant urea production, since urea is the major nitrogen-containing end product of protein catabolism, which increases markedly in burn victims.

Decreased renal perfusion (choice A) also produces increased BUN with normal serum creatinine, but you would expect to see urine output decrease as a consequence of the inadequate perfusion.

Distal urinary tract obstruction (choice B), due to processes such as stones, cancer, or benign prostatic hyperplasia, causes both BUN and serum creatinine to rise, but the rise in serum urea is proportionally higher than that of serum creatinine.

In renal glomerular disease (choice D) of sufficient severity to cause acute or chronic renal failure, creatinine and urea usually rise in parallel.

In renal tubulointerstitial disease (choice E), notably in acute tubular necrosis, creatinine may rise disproportionately to urea.

A 35-year-old woman is brought to an emergency department after she collapses and loses consciousness. For several hours previously, she had been complaining of severe lower abdominal pain accompanied by some nausea,

but she had not gone to a physician because she thought she just had a severe gastrointestinal infection. In the emergency room she is found to be in shock. Gynecologic examination reveals a mass lesion of one adnexa and bulging of the cul-de-sac. Serum hCG is above the normal range. Long-standing prior infection by which of the following organisms would be most likely to predispose for this woman's condition?     A. Chlamydia     B. Escherichia     C. Herpes     D. Human papilloma virus     E. Treponema

Explanation:

The correct answer is A. This case illustrates a classic presentation of ectopic pregnancy with tubular rupture and hemorrhage. The most common predisposing factor is pelvic inflammatory disease, most commonly caused by Chlamydia trachomatis or Neisseria gonorrhoeae. Other risk factors for ectopic pregnancy include prior ectopic pregnancy, exposure to diethylstilbestrol (DES), and induced abortion.

Escherichia(choice B) does not usually cause female genital disease.

Herpes (choice C), human papilloma virus (choice D), and Treponema(choice E) can all infect the female genital tract, but are not important causes of pelvic inflammatory disease.

A 62-year-old man develops premature ventricular contractions (PVCs) while receiving digoxin for the treatment of atrial fibrillation. The patient has multiple medical problems, for which he is taking several other medications. Which of the following medications is the most likely cause of this new complication?     A. Colestipol     B. Furosemide     C. Glyburide     D. Phenytoin     E. Sulfasalazine

Explanation:

The correct answer is B. Patients who develop digoxin toxicity gradually during chronic therapy are often hypokalemic and hypomagnesemic secondary to concurrent diuretic therapy. Toxicity can also occur in those with concomitant ventricular dysrhythmias. In this case, the patient's premature ventricular contractions (PVCs) are most likely related to the development of hypokalemia secondary to the overuse of furosemide, a loop diuretic. All the other agents are associated with reducing digoxin blood levels, which would decrease the risk for digoxin toxicity.

Colestipol (choice A) is a bile-acid-binding resin that is indicated for the treatment of hypercholesteremia. When given with digoxin, this agent will bind in the intestinal tract and, hence, decrease the absorption of the drug into the body.

Glyburide (choice C) is a sulfonylurea indicated for the treatment of type 2 diabetes. Medications such as glyburide and sulfasalazine, which have "sulfa" components, are associated with the lowering of serum digoxin levels.

Phenytoin (choice D) is a hydantoin antiepileptic agent indicated for the treatment of tonic-clonic and partial complex seizures. This agent increases the metabolism of digoxin; hence, it will lower digoxin levels.

Sulfasalazine (choice E) is an agent indicated for the treatment of ulcerative colitis and rheumatoid arthritis, and lowers serum digoxin levels.

A 31-year-old HIV-positive man develops a severe pneumonia. Lower respiratory tract secretions obtained by fiberoptic bronchoscopy with bronchoalveolar lavage and stained with methenamine silver stain demonstrate cup-shaped cysts with sharply outlined walls. Which of the following organisms is the most likely pathogen in this case?     A. Candida albicans     B. Giardia lamblia     C. Haemophilus influenzae     D. Pneumocystis carinii     E. Streptococcus pneumoniae

Explanation:

The correct answer is D. The organism described is Pneumocystis carinii, which is an opportunistic parasite that appears to be more closely related to fungi than to protozoa. Its cyst form, when stained with silver stains, has the distinctive appearance described in the question stem, and is typically found in frothy material that occupies the lumen of alveoli. The trophozoites are smaller and much harder to recognize. Bronchoalveolar lavage is considered much more reliable than induced sputum as a diagnostic specimen. Pneumocystis pneumonia is a common infection among AIDS patients, and is very uncommon in other clinical settings. Formerly, many AIDS patients died with Pneumocystis pneumonia, but the combination of early drug treatment (with trimethoprim/sulfamethoxazole or pentamidine) and prophylaxis (usually with

trimethoprim/sulfamethoxazole) has decreased the number of fatal infections. In severe cases, Pneumocystis infection can sometimes be demonstrated in extrapulmonary sites.

Candida albicans(choice A) can infect the lung and stain with methenamine silver, but the description of the lavage material would probably include the terms fungal hyphae and yeast forms.

Giardia lamblia (choice B) causes diarrhea, rather than pneumonia.

Haemophilus influenzae(choice C) and Streptococcus pneumoniae(choice E) are bacteria and would not stain with silver stains.

A traveler in Bogota, Colombia drinks a glass of fruit juice with ice cubes made from tap water. E. coli contaminating the water supply grow in the traveler's intestine and synthesize a protein that causes his intestinal epithelium to overproduce cyclic AMP, resulting in a watery diarrhea. This syndrome is typical of which of the pathogenic strains of E. coli?     A. Enteroaggregative      B. Enterohemorrhagic     C. Enteroinvasive     D. Enteropathogenic     E. Enterotoxigenic

Explanation:

The correct answer is E. Enterotoxigenic E. coli (ETEC), an important cause of traveler's diarrhea, produces a toxin that activates intestinal adenylate or guanylate cyclase. Consequently, the intestinal mucosa overexpresses cAMP, resulting in a mild and self-limited secretory diarrhea.

Enteroaggregative E. coli (EAEC; choice A) does not express a toxin, but is seen to cluster over the colonic mucosa in some individuals. Although occasionally found in patients with chronic diarrhea, no clear mechanism for mucosal pathophysiology has been determined for EAEC.

Enterohemorrhagic E. coli (EHEC; choice B), classically associated with strain O157:H7 and present in undercooked hamburgers, expresses a Shiga-like toxin that causes bloody diarrhea and hemolytic-uremic syndrome.

Enteroinvasive E. coli (EIEC; choice C) does not express a toxin, but rather is pathogenic through its capacity to invade the colonic mucosa and evoke an inflammatory response. The resulting dysentery-like inflammatory diarrhea generally necessitates vigilant hydration, but no antibiotics are indicated.

Enteropathogenic E. coli (EPEC; choice D) does not produce any known toxins, but adheres tightly to the glycocalyx of the colonic mucosa and disrupts the microvilli. Villous atrophy, mucosal thinning, and inflammation in the lamina propria, are produced, resulting in impaired absorption and diarrhea.

A 34-year-old man develops pulmonary hemorrhage and glomerulonephritis. Lung biopsy with immunofluorescence demonstrates IgG deposition along the basement membrane. These antibodies are most likely directed against which of the following types of collagen?     A. Type I     B. Type II     C. Type III     D. Type IV     E. Type X

Explanation:

The correct answer is D. The disease described is Goodpasture's syndrome, in which autoantibodies to basement membrane proteins cause damage to the lungs and kidneys. Pulmonary hemorrhage (especially in smokers) and rapidly progressive glomerulonephritis are common. The characteristic autoantibody present is directed against Type IV collagen, a component of the basement membrane.

Type I collagen (choice A) is found in bone, skin, tendon, dentin, fascia, and late wound repair.

Type II collagen (choice B) is found in cartilage (including hyaline cartilage), the vitreous body of the eye, and the nucleus pulposus of the intervertebral disks.

Type III collagen (choice C) is found in skin, blood vessels, uterus, fetal tissue, and granulation tissue.

Type X collagen (choice E) is found in epiphyseal plates.

A 54-year-old man with a long history of smoking is diagnosed with squamous cell carcinoma of the larynx. During the course of a radical neck dissection to remove the tumor and regional lymph nodes, the spinal accessory nerve is severed. As a result, the man would most likely have the greatest difficulty in     A. abducting the arm     B. adducting the arm     C. elevating the point of the shoulder (shrugging)     D. laterally rotating the arm     E. medially rotating the arm

Explanation:

The correct answer is C. The spinal accessory nerve (cranial nerve XI) is a motor nerve (special visceral efferent) that innervates the sternocleidomastoid and trapezius muscles. The trapezius, a broad, flat, triangular muscle, has fibers in its superior part that originate from the external occipital protuberance and the superior nuchal line, the ligamentum nuchae, and the spinous processes of vertebrae C-7 through T-4. These upper fibers pass laterally to insert onto the acromion and the spine of the scapula. Activation of this part of the muscle results in elevation of the point of the shoulder (acromion moves superiorly), as in shrugging.

The muscles that promote movement of the arm away from the midline of the body (abduction, choice A) include the deltoid, subscapularis, supraspinatus, and infraspinatus muscles which are innervated by branches of the brachial plexus, not the spinal accessory nerve (CN XI). When there is damage to the spinal accessory nerve, they may also have difficulty elevating (abducting) the arm above a horizontal plane because the superior fibers of the trapezius, along with the serratus anterior, externally rotate the scapula about an anteroposterior axis, which is required for elevation of the arm beyond a horizontal plante. However, this is a question of “magnitude”: loss of trapezius function would have greater effect on scapular elevation than rotation (i.e. serratus anterior is better able to comensate for loss of external rotation than levator scapulae can for elevation).

The trapezius adducts the scapula, whereas the major arm adductors (choice B) include the pectoralis major, teres major, latissimus dorsi, and coracobrachialis muscles. These muscles are innervated by branches of the brachial plexus.

The muscles that act to laterally rotate the arm (choice D) include the teres minor, infraspinatus, supraspinatus, and the dorsal portion of the deltoid muscles. These muscles are innervated by branches of the brachial plexus, not the spinal accessory nerve (CN XI).

The medial rotators of the arm (choice E) include the subscapularis, the ventral part of the

deltoid, the latissimus dorsi, and the teres major muscles, all of which are innervated by branches of the brachial plexus.

An 18-year-old man is evaluated for possible immunodeficiency disease because of a life-long history of chronic lung infections, recurrent otitis media, and multiple episodes of bacterial meningitis. While total IgG is normal, the patient is found to have a selective deficiency of IgG2. IgG2 deficiency is most likely to be associated with a deficiency of which of the following other substances?     A. C3     B. C4     C. IgA     D. IgE     E. IgM

Explanation:

The correct answer is C. IgG subclass deficiency is one of the more minor forms of immunodeficiency disease, and most patients with this condition who are optimally managed can expect a normal life span. The typical presentation is as illustrated in the question stem. The deficiency may involve either or both IgG2 and IgG3 with or without IgG4 deficiency. (IgG1 is the major form, and its deficiency leads to a deficiency of total IgG, and so, by definition, it is not considered a "subclass" deficiency.) A potentially clinically important point is that some patients with IgG2 deficiency also have IgA deficiency and may develop anaphylaxis if given IgA-containing blood products.

C3 deficiency (choice A) tends to produce pyogenic infections.

C4 deficiency (choice B) tends to produce an SLE-like syndrome.

IgE deficiency (choice D) can be seen in some incomplete antibody deficiency syndromes, but is usually not clinically significant.

IgM deficiency (choice E) occurs as part of severe combined immunodeficiency.