Disclosures: Gurtej Bajaj, MD: No financial relationships or conflicts of interest

Case Diagnosis: A 78-year-old male with positional lower leg weakness and painful paresthesia.

Case Description or Program Description: A 78-year-old male with significant history of myasthenia gravis, myotonia congenita, peripheral arterial disease, and L3-L5 spinal decompression presented with progressive left lower leg pain exacerbated by extension of the knee during ambulation and relieved with knee flexion when seated. The patient presented with left-sided antalgic gait and weakness in ankle and toe dorsiflexion. MRI of the lumbar spine was unrevealing, and a CTA with runoff was notable for occlusion of the left popliteal artery with distal reconstitution. An MRI of the left calf revealed a 7.3×4.8×5.6 cm lipoma in the popliteal fossa. Electromyography demonstrated pronounced amplitude loss of the left extensor digitorum brevis and needle exam findings localized the lesion to the distal thigh. Musculoskeletal ultrasound of the popliteal fossa redemonstrated the lipoma abutting the common peroneal nerve (CPN) without gross compression. Based on the diagnostic workup, it was concluded that the lipoma was causing dynamic compression of the affected nerve. The patient was referred for surgical resection of the lipoma.

Setting: Academic outpatient clinic.

Assessment/Results: The patient experienced significant reduction in pain and improvement of lower leg strength within a month of surgery. He pursued post-operative physical therapy to achieve successful functional restoration.

Discussion (relevance): Compression of the CPN by a popliteal lipoma is uncommon, and may result in an atypical presentation. This case was rare in that the compression was dynamic, based on position, and was complicated by multiple comorbidities that may present with similar clinical findings. This case highlights the complementary use of multiple diagnostic modalities to determine proper treatment.

Conclusions: Compressive soft tissue lesions adjacent to neurovascular structures should be considered in the differential diagnosis when clinical findings are not consistent with known diagnoses or available imaging.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/dynamic-common-peroneal-nerve-compression-by-popliteal-lipoma-a-case-report/