Stimulation single-fiber EMG in infant botulism

The principal electrodiagnostic feature of infant botulism, an incremental response an high rates of repetitive nerve stimulation, has variable sensit ivity and may not always be useful as a diagnostic test given the vagaries of test timing and severity of illness. We report the use of stimulation si ngle fiber EMG (S-SFEMG) in making this clinical diagnosis, Four infants be tween 1 and 5 months of age presented with rapidly progressive bulbar and l imb weakness, internal and external ophthalmoplegia, areflexia, and comprom ised ventilation. Incremental response with high-rate repetitive nerve stim ulation and a typical clinical course for infant botulism confirmed the dia gnosis in all; stool toxin studies were positive for type B botulinum in 2 of the 3 cases in which they were obtained. S-SFEMG was performed by surfac e stimulation of median and ulnar nerves and recording with a single fiber needle in the thenar, hypothenar, or first dorsal interosseous muscles. A t otal of eight single fiber recordings were studied at rates of 2, 5, 10, an d 20 Hz. Ail single fibers studies showed an improvement with higher rates of stimulation, beginning at 10 Hz and peaking at 20 Hz. Compared to baseli ne study at 2 Hz (100%), the mean percent changes in jitter at 5, 10, and 2 0 Hz were 109, 60, and 47, respectively. This is the first report of the us efulness of S-SFEMG in the diagnosis of infant botulism, (C) 1999 John Wile y & Sons, Inc.