(Kiosk 6) Left Peroneal Neuropathy with Left Equinus and Inversion Gait Pattern Secondary to a Rattlesnake Bite: A Case Report

Case Diagnosis: Left Peroneal Neuropathy with Left Equinus and Inversion Gait Pattern

Case Description or Program Description: A 9 y/o patient was bit by a rattlesnake in her left lateral lower leg distal to the fibular head. She developed left lower extremity weakness, received 40+ doses of antivenom, monitored for compartment syndrome, and had no surgical intervention. 3.5 months later, she had continued weakness in ankle dorsiflexion and eversion 0/5 with 2+ bilateral patellar and right Achilles reflexes. Light touch sensation was decreased in a quarter-sized patch on left distal foot. Electrodiagnostic testing revealed absent left superficial peroneal sensory and absent left peroneal motor responses at the extensor digitorum brevis and tibial anterior muscles. Needle study of tibialis anterior had no insertional activity and no motor units; left peroneal longus had fibrillations and severely reduced activation with a few polyphasic, normal to low amplitude motor units. Patient had therapy and sometimes walked with a left posterior leaf spring AFO. Gait analysis 1 year later revealed increased left knee flexion at initial contact, inversion of the left foot throughout swing. Plantar pressure analysis showed increased pressure under the base and head of the 5th metatarsal on the left, and initial contact at the base of the 5th metatarsal.

Setting: Gait Lab, Children's Hospital of Colorado

Assessment/Results: With a left posterior leaf spring style AFO, she had less inversion throughout swing. With a left Vasyli insert with high top shoes, she had increased swing throughout. Orthopedic surgery recommended considering a left split posterior tibialis tendon transfer to peroneus brevis verses calcaneus or midfoot with goal to decrease left ankle inversion during stance/swing phases and improve left plantigrade foot posture during stance phase.

Discussion (relevance): Rattlesnake venom can present with myokymic discharges not appreciated on evaluation. Posterior Leaf Spring AFOs can provide assistance with dorsiflexion which was noted in her gait analysis.

Conclusions: We present a patient who developed a left peroneal neuropathy secondary to snakebite. We would expect dorsiflexion and inversion weakness of tibialis anterior secondary to deep peroneal nerve injury and absent superficial peroneal sensation. We typically think about fibular head injury affecting both branches of peroneal nerve.