SOX1 proteins play a vital role in central nervous system development. Anti-SOX1 antibodies have been associated with various paraneoplastic syndromes including Lambert Eaton Myasthenic Syndrome (LEMS), paraneoplastic cerebellar degeneration (PCD), paraneoplastic limbic encephalitis (PLE), and neuropathy. LEMS is the most common clinical symptom in patients with anti-SOX1 antibodies, followed by PCD. Classic PCD has a subacute course of a severe cerebellar syndrome usually without any evidence of cerebellar atrophy in brain MRI. PCD patients present with various cerebellar ataxia symptoms such as ataxia, dysmetria, dysarthria, nystagmus, dizziness, and vertigo.  Anti-SOX1 antibodies' positive paraneoplastic neurological disorders are rare and are usually associated with small cell lung cancer (SCLC).  However, there are only a few case reports of PCD association with autoantibodies in other types of cancer.

A 64-year-old Caucasian man with history of prostate cancer who underwent radical prostatectomy after the diagnosis, presented with slowly progressive unsteady gait, infrequent falls, and tremor for the last 3 months. Neurological exam was abnormal only for vertical nystagmus, impaired tandem gait and slight intentional tremor of bilateral hands. Brain MRI was unremarkable for any acute intracranial pathology, brain metastasis or cerebellar atrophy. Initially blood work up for ataxia including Vitamin B12, Vitamin E, thiamine, heavy metal serum levels, and serum preneoplastic antibody panel was unremarkable except for an elevated level of anti-SOX1 antibody in serum. Patient was started on IVIG 0.4 grams/kg per day for 5 days with possible paraneoplastic cerebellar degeneration (PCD) diagnosis. Partial improvement of symptoms was noted in few weeks.

PCD is extremely rare in patients with prostate cancer and anti-Hu is the most commonly found onconeural antibody in these cases. To the best of our knowledge, this is the first case of anti SOX1 antibody associated PCD in a patient with prostate cancer.