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

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

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