Bickerstaff was excluded by the absence of encephalopathy, hyperreflexia, or MRI abnormalities; myasthenia gravis was ruled out by negative AChR and MuSK antibodies and preserved neuromuscular transmission; and a paraneoplastic etiology was considered unlikely given negative antibody panels, stable tumor activity, and the close temporal relationship to avelumab exposure. The gene discussed is MUSK; the disease is myasthenia gravis.