Myopathy

1. What are seven different categories of myopathy?
2. What is the clinical presentation of myopathy?
3. What is seen on EMG in myopathy?
4. What is the utility of quantitative EMG for myopathy?
5. What is seen with rep stim and SFEMG in myopathy?
6. Which disorders show Type II fiber atrophy on biopsy?

Answers:
1. Dystrophic (Duchenne, Becker), congenital, metabolic (acid maltase deficiency), inflammatory (polymyositis, dermatomyositis), endocrine (thyroid, adrenal), toxic (alcohol, diuretics, vincristine), steroids.
2. Muscle atrophy, hypertrophy, abnormal MSR, weakness, hypotonia, gait abnormalities, or myotonia (painless delayed relaxation of muscles).
3. SNAP normal, CMAP low amplitude, EMG may show fibs, PSW, CRD, or myotonic discharges. Classic MUAPs are small duration, small amplitude due to loss of muscle fibers, but collateral sprouting may result in long duration large amplitude MUAPs. MUAPs may be unstable at the beginning of sprouting.
4. Used to calculate mean duration by using 20 MUAPs.
5. Rep stim may show a decremental response due to reduced safety factor in regenerating immature NMJs. SFEMG shows increased jitter, fiber density, and blocking.
6. Steroid myopathy, myasthenia gravis, deconditioning.