Myopathies and their Electrodiagnosis2Myopathies and their Electrodiagnosis2
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
RememberRemember
STEROIDS QUIET MUSCLE MEMBRANES
EMG PIN CAN CAUSE PROBLEMS WITH MUSCLE BIOPSY
DUCHENNE MUSCULAR DYSTROPHYDUCHENNE MUSCULAR DYSTROPHY
Family History, Sex-linked Recessive Pseudohypertrophy CK elevation Reduced or Absent Dystrophin Gene Deletion EMG shows fibs, positive waves, myopathic
changes early, but hard to find muscle later
DUCHENNE MUSCULAR DYSTROPHYDUCHENNE MUSCULAR DYSTROPHY 30 per 100,000 live births 1/3 of cases are new mutations x-linked recessive Female carriers with mild weakness
and CK elevation due to Lyon hypothesis
CREATINE KINASE IN DMDCREATINE KINASE IN DMD
Begins in infancy at 50-100 times normal (usually 10,000 to 30,000)
Declines about 20% per year CK less than 10 times normal is strong
evidence against DMD, except in final stages
Can be in normal range in last stage
GENE ABNORMALITY IN DMD GENE ABNORMALITY IN DMD
Located at Xp21 (1977) DMD gene is large (2000 kilobases) (cloned in 1987)
The largest gene Gene produces Dystrophin (1987) Southern blot or Polymerase chain reaction (PCR)
identifies gene deletions (present in about 60%) Sporadic cases due to new mutation or germ line
mosaicism Carriers who are negative for gene deletion can be
identified by Linkage Analysis
DYSTROPHIN (1987)DYSTROPHIN (1987) Pattern for making it is on Xp21 gene Only 0.002% of striated muscle protein Critical to the muscle membrane structure
(sarcolemma) (1988) MDX mouse also has no dystrophin, inherits its
disease as x-linked recessive, but has only minor weakness
Dystrophin is also found in smooth muscle, cardiac muscle , neurons and glia
Carriers have reduced dystrophin
BECKER MUSCULAR DYSTROPHY BECKER MUSCULAR DYSTROPHY
High CK Pseudohypertrophy Sex-Linked Recessive EMG Reduced or abnormal dystrophin Gene deletion
LIMB GIRDLE MDLIMB GIRDLE MD Autosomal Recessive usually Onset usually in 20’s-30’s EMG shows myopathic units, mild
muscle membrane irritability This is a number of diseases we are now
genetically separating
FASCIOSCAPULOHUMERAL Muscular DystrophyFASCIOSCAPULOHUMERAL Muscular Dystrophy Autosomal Dominant Pattern of Weakness, especially of
face Can’t whistle, suck through straw EMG shows myopathic potentials,
rare positive wave or fibrillation