Intraarterial secobarbital: muscle injury evaluated by electrodiagnosis in four cases.

A syndrome of severe upper extremity pain, swelling and weakness following intraarterial injection of illicit secobarbital was evaluated in 4 patients. Although the involved muscle mass was small, serum muscle enzymes were markedly elevated. Electromyography (emg) revealed fibrillation and positive sharp wave potentials at 7 days. Motor unit action potentials were of low amplitude and of brief duration but markedly reduced in numbers, a mixture of myopathic and neuropathic changes. Motor nerve conduction velocities and latencies were normal, but M-wave amplitudes were small. Serial studies in 1 patient revealed persistent fibrillation and positive sharp waves in all involved muscles with absent voluntary contraction in the ulnar muscles and no response to stimulation of the ulnar nerve at 60 days postinjection. The emg and conduction studies for the median nerve distribution were normal except for the abnormal rest activity. A muscle biopsy (on day 66) in this patient revealed findings compatible with neuropathy, myopathy and vasculitis. The results indicate that electrodiagnostic studies may be of value for prognosis in these cases by evaluating the extent of neuromyopathic involvement.