myopathies and their electrodiagnosis3 randall l. braddom, m.d., m.s. clinical professor robert wood...
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Myopathies and their Electrodiagnosis3Myopathies and their Electrodiagnosis3
Randall L. Braddom, M.D., M.S.
Clinical Professor
Robert Wood Johnson Medical School and the New Jersey Medical School
The Five Steps of EMG First published by Johnson and
Melvin in 1971. Johnson EW, Melvin JL. Value of
electromyography in lumbar radiculopathy. Arch Phys Med Rehabil (June) 1971. 52: 239-243
COLLAGEN-VASCULAR MYOPATHIESCOLLAGEN-VASCULAR MYOPATHIES
Dermatomyositis Polymyositis Scleromyositis Rheumatoid myositis
DERMATOMYOSITISDERMATOMYOSITIS Bimodal distribution Weakness, skin rash, malaise Weight loss, fever Eyelid rash Skin calcifications Telangiectasia Malignancy association in adults
POLYMYOSITISPOLYMYOSITIS Weakness No skin lesions Associated with malignancy May have dysphagia Weight loss
INFECTIOUS MYOSITISINFECTIOUS MYOSITIS
Trichinosis Cysticercosis (Taenia
solium) Viral
ENDOCRINE MYOPATHIESENDOCRINE MYOPATHIES
Hyperthyroid Hypothyroid Cushings Disease/Steroids Hypoparathyroid Hyperparathyroid
CONGENITAL MYOPATHIESCONGENITAL MYOPATHIES
Central Core Myotubular Nemaline Rod Fiber Type Dysproportion Mitochondrial
Conditions Having Both Clinical and EMG MyotoniaConditions Having Both Clinical and EMG Myotonia
Myotonic Dystrophy MD1 MD2 (proximal myotonic
myopathy) Myotonia Congenita Schwartz-Jampel Syndrome
Myotonic potentials (from Dumitru)
MD 1 (Classic Myotonic Dystrophy) Cranial muscle wasting/weakness Distal weakness more than proximal Hatchet” face Dysphagia, Dysarthria First degree heart block/bundle branch block/
arythmias Cataracts Frontal baldness Genetics: Autosomal dominant CTG Repeat
Disorder
CLINICAL MYOTONIACLINICAL MYOTONIA
Sustained contraction of muscle caused by spontaneous repetitive depolarization of the muscle membrane
Arises from the muscle membrane...denervation does not stop it
Painless Diminishes with exercise (warm-up phenomenon) Worsened by cold Action or percussion myotonia
Clinical Tests of Myotonia Percussion: the “Myotonic Phenomenon” Shake hands test
Repeatedly shake hands Delayed release of the hand that gets better on
repetition
Close and open eyes test Repeatedly close eyes tightly
Lag in opening the eyes that improves with repetition
Percussion Myotonia (Pourmand)
MD 2 Proximal Myotonic Dystrophy
Findings same as MD 1 except: Different type of CTG expansion Weakness is proximal rather than distal More frequent insulin resistance Later (Adult) onset No congenital type of MD 2
ELECTRICAL MYOTONIAELECTRICAL MYOTONIA
Increases after rest Two types of potentials resembling
fibrillations positive wave
Wax and wane in frequency and amplitude 20-80 Hertz Decremental response to high frequency
stim
Exercise Testing for Myotonia 10-30 seconds of exercise causes
decrement in CMAP in MD1 (not MD2) 5 minutes of exercise
Paramyotonia congenita has rapid decrease in CMAP with slow recovery over 60 minutes
In Periodic Paralysis the CMAP increases, then declines slowly over 30 minutes
Cooling Test for Myotonia Cooling at 15 C for 15 minutes
CMAP in paramyotonia congenita drops 75% Triggers weakness
Myotonic Dystrophy GeneticsMyotonic Dystrophy Genetics
The gene defect is an “expansion” Consequently, it is usually much worse
if inherited from the mother Inheritance from the mother can give
“Congenital Myotonic Dystrophy” A severe case in an infant can even be fatal
CLINICAL PARAMYOTONIA WITH EMG MYOTONIA
Paramyotonia Congenita Hyperkalemic Periodic Paralysis
Both give periodic attacks of weakness
Both are sodium channelopathies Hypokalemic Periodic Paralysis does not
show paramyotonia clinically or myotonia on EMG
Muscle Sodium Channelopathies Many undoubtedly exist Common one is gene SCN4A chromosome
17q23,1-25.3 This produces
PAM (Potassium aggravated myotonia) Paramyotonia congenita (PMC) Hyperkalemic periodic paralysis (HPP)
Muscle Sodium Channelopathies The defect is in the fast inactivation of the sodium
channel after depolarization occurs Rate of activation is slowed, or channel opens to
soon, or channel bursts when used a lot in a short time, or inactivation process is uncoupled from voltage dependence
End result is that there is too much intracellular sodium, causing spontaneous depolarizations in a progressive cascade effect
Only 2% of mutant channels need to be present in a muscle membrane to cause this
Muscle Chloride Channelopathies Chloride channel gene CLCNa chromosome
7q35 Thomsen’s myotonia congenita (autosomal
dominant) OR Becker’s myotonia congenita (autosomal
recessive) Mechanism for myotonic dystrophy is yet
unknown
ELECTRICAL MYOTONIA WITHOUT CLINICAL MYOTONIA Acid Maltase Deficiency
Glycogenosis Type II Glycogen storage disease
Slowly progressive truncal and proximal limb weakness
Death usually due to respiratory muscle weakness EMG shows myotonic discharges, fibs, positive
waves, CRDs, and small MUAP. Heart and liver NOT enlarged Elevated CK
Myotonic Dystrophy FactoidMyotonic Dystrophy Factoid
The weakness and the myotonia tend to be worse in distal muscles, especially the hands and the feet
EMG DISEASE Wiechers and Johnson 1979
Patients with positive waves in every muscle
No symptoms Thought it might be “form fruste” of
myotonic dystrophy
EMG DISEASE Mitchell and Bertorini 2007 (Arch Phys Med Rehabil 88:1212-
1213)
2 patients with EMG disease found to have CLCN1 gene abnormal But no repeat expansions
One patient had elevated CK and one had minimal myotonic phenomenon
Speculate that this is very mild version of Myotonic Dystrophy
SELECTIVE MUSCLE FIBER ATROPHYSELECTIVE MUSCLE FIBER ATROPHY
Type 1 Myotonic dystrophy Centronuclear myopathy
Type 2 Corticosteroids Hyperthyroidism Disuse atrophy Cachexia Central nervous system disease
www.neuro.wustl.edu/neuromuscularwww.neuro.wustl.edu/neuromuscular
Best internet site for neuromuscular diseases, including myopathies
Kept up to date Dx, Rx, Pathology,
Genetics, etc.