Myokymia in obstetrically related brachial plexopathy.

Myokymic discharges are spontaneous bursts of semirhythmic potentials that are sometimes correlated with rippling movements of skin and muscle. They have been reported in limb muscles in patients with Guillain-Barré syndrome, spinal stenosis, nerve root and nerve compression, and envenomations. They commonly occur with radiation induced plexopathies (approximately 60% of patients), but have not been reported in obstetrically related brachial plexopathies. We report 2 instances of myokymia in children with obstetric brachial plexus palsies. Each child was studied twice, and it was only at the later study, when the child was 10 or 11 months of age, that these potentials were noted. This could represent ongoing recovery from lesions incurred at birth or developmental changes. The final common pathway of all causes of myokymia could be to generate axonal membrane hyperexcitability.