(Kiosk 3) Bilateral Common Fibular Neuropathy Secondary to Rapid, Intentional Weight Loss: A Case Report

Case Diagnosis: Bilateral Common Fibular Neuropathy

Case Description: A 30-year-old female with no significant past medical history presented for evaluation of bilateral foot drop. She initially developed left foot drop several months prior. EMG/NCS at that time showed left common fibular mononeuropathy localized to the fibular head. She underwent several weeks of physical therapy with only minimal functional improvement. She subsequently developed right foot drop about 5 months later. Repeat EMG/NCS demonstrated bilateral common fibular mononeuropathy. Of note, she reported intentional weight loss of approximately 40 pounds over a 10-month period under the direction of a dietician.

Discussion: Common fibular neuropathy (CFN) is a common cause of foot drop. It usually occurs due to compression of the common fibular nerve at the fibular head. CFN classically presents with acute weakness with ankle dorsiflexion and ankle eversion in addition to sensory deficits affecting the lateral, lower leg and foot. The common fibular nerve runs superficially as it wraps around the fibular head, which predisposes it to trauma and pressure palsies. When CFN develops due to weight loss, it usually presents in the setting of gastric bypass or anorexia and occurs unilaterally. It is hypothesized that rapid weight loss results in decreased subcutaneous and perineural fat, which could increase the risk of pressure or traction-related injuries.

Setting: Outpatient PM&R Clinic at UNC

Assessment/Results: MRI lumbar spine was unremarkable. Ultrasound showed an osteophyte at the posterior left proximal fibula but no other structural abnormalities to explain bilateral CFN. Labs were largely unremarkable.

Conclusion: CFN is a common cause of foot drop, and most often occurs due to compression of the common fibular nerve at the fibular head. CFN classically presents with acute weakness with ankle dorsiflexion and ankle eversion in addition to sensory deficits affecting the lower, lateral leg and the foot. CFN can also occur due to rapid weight loss.