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

rlbraddom@comcast.net

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.