Repetitive Stimulation of the Common Peroneal Nerve as a Diagnostic Aid for Botulism in Foals

Background: Botulism is a potentially fatal paralytic disorder for which definitive diagnosis is difficult. Objectives: To determine if repetitive stimulation of the common peroneal nerve will aid in the diagnosis of botulism in foals. Animals: Four control and 3 affected foals. Methods: Validation of the test in healthy foals for its comparison in foals with suspected botulism. Controls were anesthetized and affected foals were sedated to avoid risks of anesthesia. The common peroneal nerve was chosen for its superficial location and easy access. Stimulating electrodes were placed along the common peroneal nerve. For recording, the active and reference electrodes were positioned over the midpoint and distal end of the extensor digitorum longus muscle, respectively. Repeated supramaximal stimulation of the nerve was performed utilizing a range of frequencies (1–50 Hz). Data analysis consisted of measuring the amplitude and area under the curve for each M wave and converting these values into percentages of decrement or increment based on the comparison of subsequent potentials to the initial one (baseline) within each set. Results: A decremental response was seen at all frequencies in control foals. Decremental responses also were observed in affected foals at low frequencies. An incremental response was seen in all affected foals at 50 Hz. Conclusions and Clinical Importance: Decreased baseline M wave amplitudes with incremental responses at high rates are supportive of botulism. Repetitive nerve stimulation is a safe, simple, fast, and noninvasive technique that can aid in the diagnosis of suspected botulism in foals.