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Myopathies and their Electrodiagnosis3 Randall L. Braddom, M.D., M.S. Clinical Professor Robert Wood Johnson Medical School and the New Jersey Medical School [email protected] 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 MYOPATHIES Dermatomyositis Polymyositis Scleromyositis Rheumatoid myositis DERMATOMYOSITIS Bimodal distribution Weakness, skin rash, malaise Weight loss, fever Eyelid rash Skin calcifications Telangiectasia Malignancy association in adults POLYMYOSITIS Weakness No skin lesions Associated with malignancy May have dysphagia Weight loss INFECTIOUS MYOSITIS Trichinosis Cysticercosis solium) Viral (Taenia ENDOCRINE MYOPATHIES Hyperthyroid Hypothyroid Cushings Disease/Steroids Hypoparathyroid Hyperparathyroid CONGENITAL MYOPATHIES Central Core Myotubular Nemaline Rod Fiber Type Dysproportion Mitochondrial Conditions 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 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 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 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 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 88:12121213) 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 ATROPHY Type 1 Myotonic dystrophy Centronuclear myopathy Type 2 Corticosteroids Hyperthyroidism Disuse atrophy Cachexia Central nervous system disease www.neuro.wustl.edu/neuromuscular Best internet site for neuromuscular diseases, including myopathies Kept up to date Dx, Rx, Pathology, Genetics, etc.