Julie Silverman, MD and Susan Merel, MDUniversity of Washington

Lambert Eaton Myasthenic Syndrome: An Elusive Diagnosis

Patient underwent extensive cardiopulmonary workup including unremarkable electrocardiogram, transthoracic echocardiogram, myocardial scintigraphy study, chest CT scan and pulmonary function tests.

Over the next several months, the patient was hospitalized five times at four different hospitals. The chief complaints included nausea and vomiting, difficulty swallowing and profound fatigue.

She was seen by a variety of specialty services, including neurology, gastroenterology, otolaryngology, speech therapy and rehabilitation medicine. More diagnostic studies were performed, including a barium swallow study, esophageal manometry, laryngoscopy, head and neck CTs and repeat chest, abdomen and pelvis CT scans.

Patient was ultimately admitted to the University of Washington with severe hyponatremia (Na 112 mEq/L), due to hypovolemia and SSRI-induced SIADH. Despite normalization of sodium, patient’s symptoms of weakness, malaise and autonomic dysfunction continued, prompting further investigation. An electromyogram (EMG) with repetitive stimulation was performed, which showed a disorder of presynaptic neurotransmission consistent with LEMS. 

Patient underwent extensive malignancy workup – including CT chest, abdomen, pelvis, PET scan and serum tumor markers – which returned negative. She was started on pyridostigmine and 3,4-DAP with subjective improvement in symptoms within days of starting treatment.

This case illustrates the potential difficulty of diagnosing LEMS. At time of her diagnosis, which was six months after initial presentation, the patient had been hospitalized at five different institutions, undergone more than a dozen studies and procedures and had been evaluated by at least six different subspecialty services. 

LEMS is important to consider in older patients presenting with weakness and autonomic dysfunction. While the prevalence of LEMS is low, recognition of this syndrome is critical, as up to seventy percent of patients with LEMS have an underlying malignancy. Additionally, treatment can be quite effective in reducing symptoms.

Past Medical History Social HistoryHypertension MarriedHyperlipidemia Retired office managerOsteoarthritis Lifelong non-smokerMild mitral insufficiency Rare alcohol use

Past Surgical History MedicationsUnilateral oophorectomy AtenololAppendectomy LosartanHysterectomy Triamterene-HCTZLeft knee arthroscopy SimvastatinLeft knee arthroplasty Omeprazole

PyridoxineFamily History Flax seed oilMother died from asthma Vitamin C

A 70-year-old previously healthy woman presented to her primary care physician with concerns of dyspnea, orthopnea and peripheral edema. Review of systems further revealed malaise, fatigue, muscle weakness, nausea and excessive thirst.

Lambert Eaton Myasthenic Syndrome (LEMS) is an uncommon disorder of the neuromuscular junction in which antibodies are made against presynaptic voltage-gated calcium channels. Approximately 50-70% of people diagnosed with LEMS are found to have an underlying malignancy. Symptoms of LEMS include proximal muscle weakness, fatigue and autonomic dysfunction. Although these symptoms are well-described, the diagnosis of LEMS can be difficult to make due to the non-specificity of symptoms as well as the rarity of the disease. The annual incidence is 0.48 per million population.

Background

Concerned that depression might be the cause of the patient's symptoms, patient's primary care provider started her on a selective serotonin reuptake inhibitor (SSRI). Patient denied improvement in symptoms with SSRI.

Case Report

Discussion

Patient's symptoms continued, with worsening dry mouth, anorexia and unintentional fifteen-pound weight loss over the next two months. An EGD, colonoscopy, abdominal ultrasound and abdominal CT scan were obtained, all of which were unrevealing.