Refractory Thigh Pain Revealing Femoral Neuritis in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis: A Case Report.

Peripheral nervous system involvement is a possible manifestation of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). We present a case of a 48-year-old female patient with known AAV presenting with refractory left thigh pain. She underwent extensive workup for musculoskeletal, spinal, and vascular causes of her pain that were all unrevealing. Physical examination localized her pain to the femoral nerve, and magnetic resonance imaging (MRI) of the pelvis with neurography revealed findings consistent with femoral neuritis. She was promptly started on immunosuppressive treatment, which resulted in dramatic improvement in her pain. This case demonstrates that vasculitic neuropathy may present as a painful proximal mononeuropathy. Neurologic localization and targeted magnetic resonance neurography should be considered when conventional evaluation fails to explain intractable focal extremity pain in a patient with systemic vasculitis.