200 Section - Electrodiagnostic Confirmation of Peroneal Neuropathy Following Glucagon-Like Peptide Therapy–Associated Rapid Weight Loss

A 42-year-old female with type 2 diabetes mellitus developed right-sided common peroneal neuropathy following rapid weight loss induced by weekly Glucagon-Like Peptide-1 receptor agonist therapy. Over 11 months, the patient lost 23.1 Kg and developed right foot drop, numbness, and paresthesia along the peroneal distribution. Examination revealed flaccid ankle dorsiflexion and eversion with preserved plantarflexion and inversion. Ultrasound findings 1 month after symptom onset showed no compression or nerve enlargement. EMG confirmed common peroneal neuropathy, secondary to rapid loss of the protective fat-pad around the fibular head.  

Case Description:

Initial EMG study 1 month after symptom onset revealed intact sensory conduction but impaired motor conduction across the fibular head. Motor conduction velocity was markedly reduced at the knee–fibular head segment. Needle study showed fibrillations, positive sharp waves, and reduced recruitment in the tibialis anterior and peroneus longus. A repeat EMG 2 months later demonstrated further slowing at the knee-fibular head segment. Needle study revealed continued denervation changes at the tibialis anterior and peroneal longus. The tibialis posterior, gastrocnemius, and vastus lateralis remained normal on both studies, further localizing the lesion to the common peroneal nerve.

Discussions:

Electrodiagnostic testing was crucial in distinguishing the etiology of rapid weight loss induced focal neuropathy from trauma or diabetic neuropathy. While clinical findings such as foot drop raised suspicion, serial EMG findings provided definitive evidence of a focal lesion at the fibular head affecting the common peroneal nerve.

Conclusions:

This case highlights the diagnostic value of EMG studies in identifying focal neuropathies associated with rapid weight loss. As GLP-1 therapy for weight loss becomes increasingly prevalent, electrodiagnostic testing offers an early, non-invasive method for localizing nerve injuries, differentiating etiologies, and guiding timely management.