Transcript Myopathies and their Electrodiag

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
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First published by Johnson and
Melvin in 1971.
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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
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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
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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
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Conditions Having Both Clinical
and EMG Myotonia
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Myotonic Dystrophy
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MD1
MD2 (proximal myotonic
myopathy)
Myotonia Congenita
 Schwartz-Jampel Syndrome
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Myotonic potentials (from Dumitru)
MD 1 (Classic Myotonic Dystrophy)
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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
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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
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Percussion: the “Myotonic Phenomenon”
Shake hands test
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Repeatedly shake hands
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Delayed release of the hand that gets better on
repetition
Close and open eyes test
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Repeatedly close eyes tightly
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Lag in opening the eyes that improves with repetition
Percussion Myotonia (Pourmand)
MD 2 Proximal Myotonic Dystrophy
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Findings same as MD 1 except:
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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
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Increases after rest
Two types of potentials resembling
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fibrillations
positive wave
Wax and wane in frequency and amplitude
20-80 Hertz
Decremental response to high frequency
stim
Exercise Testing for Myotonia
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10-30 seconds of exercise causes
decrement in CMAP in MD1 (not MD2)
5 minutes of exercise
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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
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Cooling at 15 C for 15 minutes
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CMAP in paramyotonia congenita drops 75%
Triggers weakness
Myotonic Dystrophy Genetics
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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”
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A severe case in an infant can even be fatal
CLINICAL PARAMYOTONIA WITH
EMG MYOTONIA
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Paramyotonia Congenita
Hyperkalemic Periodic Paralysis
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Both give periodic attacks of
weakness
Both are sodium channelopathies
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Hypokalemic Periodic Paralysis does not
show paramyotonia clinically or myotonia on
EMG
Muscle Sodium Channelopathies
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Many undoubtedly exist
Common one is gene SCN4A chromosome
17q23,1-25.3
This produces
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PAM (Potassium aggravated myotonia)
Paramyotonia congenita (PMC)
Hyperkalemic periodic paralysis (HPP)
Muscle Sodium Channelopathies
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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
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Chloride channel gene CLCNa chromosome
7q35
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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
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Acid Maltase Deficiency
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Glycogenosis Type II
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Glycogen storage disease
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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
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The weakness and the myotonia tend
to be worse in distal muscles,
especially the hands and the feet
EMG DISEASE
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Wiechers and Johnson 1979
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Patients with positive waves in every
muscle
No symptoms
Thought it might be “form fruste” of
myotonic dystrophy
EMG DISEASE
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Mitchell and Bertorini 2007 (Arch Phys Med Rehabil 88:12121213)
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2 patients with EMG disease found to have
CLCN1 gene abnormal
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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
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Type 1
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Myotonic dystrophy
Centronuclear myopathy
Type 2
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Corticosteroids
Hyperthyroidism
Disuse atrophy
Cachexia
Central nervous system disease
www.neuro.wustl.edu/neuromuscular
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Best internet
site for
neuromuscular
diseases, including
myopathies
Kept up to date
Dx, Rx, Pathology,
Genetics, etc.