Clinical electrophysiology of infantile botulism.

Infantile botulism is a recently recognized cause of acute hypotonic paresis and respiratory failure in young infants. Electrophysiological testing has proven useful in early diagnosis in suspected cases by demonstrating abnormal neuromuscular transmission as is known to occur in botulism. Twenty-five infants with bacteriologically proven botulism were studied by uniform methods in our laboratory and characteristic electrophysiological abnormalities were found. Repetitive stimulation at 20 and 50 Hz was the most specific single test; 23 patients (92%) showed incremental responses. Stimulation at low rates was less specific. Concentric needle electromyography provided useful supplemental information. Short-duration, low-amplitude motor unit potentials were prominent in 22 patients (92%) accompanied by abnormal spontaneous activity in 13 patients (54%). Compound muscle action potential amplitudes were usually reduced, but motor and sensory conduction studies were otherwise normal. Electrodiagnostic testing demonstrated one or more characteristic abnormalities in all cases of infantile botulism. This constellation of electrophysiological abnormalities, combined with an appropriate clinical picture, was so distinctive as to allow early presumptive diagnosis of infant botulism, before the results of bacteriological testing were available.