A 62-year-old male with a history of HIV (on antiretroviral therapy, CD4 688) presented with a one month history of acute, asymmetric, progressive, painful, bilateral lower extremity weakness and sensory symptoms, starting acutely in his left foot with involvement of right foot one week later. He also reported constitutional symptoms and orthostatic intolerance. Neurological exam revealed ankle dorsiflexion weakness, absent Achilles reflex, and diminished sensation to multiple sensory modalities in the distal lower extremities. Profound orthostatic hypotension was observed. EMG/NCS was suggestive of mononeuropathy multiplex, concerning for MM in the clinical context. Serum and cerebrospinal fluid testing for inflammatory processes (including vasculitiides) was unrevealing. MRI brain/spine were unremarkable. Pathology from sural nerve and fibularis brevis muscle biopsies were non-specific, showing evidence of a neurogenic process with demyelinating and axonal features and myopathy, respectively, but unable to characterize a specific disease process. CT chest/abdomen/pelvis was normal. PET/CT was performed to evaluate for a paraneoplastic process, and revealed pathological FDG activity involving medium vessels diffusely, including in the lower extremities. Overall, this was suggestive of a medium vessel vasculitis. The patient was treated with a five-day course of methylprednisolone followed by cyclophosphamide, with improvement in symptoms at one-month follow-up.