Anti-SOX1 antibody paraneoplastic cerebellar degeneration and delayed presentation of small cell carcinoma

<h3></h3> A 64-year-old man presented with acute onset diplopia, gait instability and left facial weakness. Examination revealed an asymmetric left-sided cerebellar syndrome and a left upper motor neurone facial weakness. MRI head demonstrated subtle ischaemic changes in the right motor strip, but no cerebellar abnormalities. Lumbar puncture revealed unmatched oligoclonal bands. Serum autoimmune antibody screen identified anti-SOX1 antibodies. He was treated with IV methylprednisolone and plasma exchange which resulted in a sustained but partial symptomatic improvement. CT-PET screening 3 years after presentation demonstrated an FDG avid retroperitoneal lymph node which on biopsy reportedly demonstrated granulomatous inflammation. Two years later he developed an abdominal mass, weight loss and anaemia. CT imaging revealed a large retroperitoneal mass and para-aortic lymphadenopathy. Biopsy revealed a poorly differentiated small cell TTF-1 positive tumour, suggestive of primary small cell lung carcinoma. He was treated with chemotherapy but died of pulmonary embolism 8 years after neurological presentation with only small volume residual tumour. Retrospective analysis of the initial lymph node biopsy identified the presence of carcinoma cells. In this case anti-SOX1 immunoreactivity appears to be associated with an atypical, delayed presentation and more benign course of a histologically confirmed small cell carcinoma.