Adult-onset Still’s disease (AOSD) is a rare inflammatory disorder characterized by a classical triad of spiking fever, arthritis, and evanescent rash. Neurological involvement in AOSD is quite infrequent with reported prevalence less than 10%.

52-year-old male with medical history of AOSD, obstructive sleep apnea and bipolar disorder presented to neurology clinic for muscle fatigue and weakness. Patient was diagnosed with AOSD based on Yamaguchi criteria.

Physical examination was notable for reduced sensation to light touch and pinprick in four toes bilaterally excluding 5th toe. Normal muscle tone, strength, and reflexes were noted. Cranial nerve examination was normal. Extended myositis panel was negative. Patient underwent MRI of the pelvis which showed mild to moderate myositis to the gluteal muscles and anterior compartments in bilateral thighs. Patient underwent EMG which demonstrated mildly prolonged peak latency with normal amplitude in sensory nerve action potential (SNAP) in right median nerve.  Mildly slowed conduction velocity with normal distal latency and normal amplitude was also noted on compound muscle action potential (CMAP) in right median nerve. EMG of right lower extremity demonstrated increased recruitment of small amplitude short duration polyphasic MUAPs observed in the vastus lateralis and tibialis anterior muscles. The EMG findings were consistent with non-irritable myopathy. Given rest of the myositis work up was unremarkable, the presentation was likely related to neurological manifestations of ASOD. Patient was continued on prednisone ands weekly Tocilizumab.