Paraneoplastic neurological syndrome due to burned-out testicular tumor showing hot cross-bun sign

Background Paraneoplastic neurological syndromes (PNS) are rare remote effect of cancer. The antibodies and tumors associated with PNS have been well described, but there are still many clinically suspected cases in which no tumor or antibody can be identified. This is the first report of PNS showing hot cross-bun sign and caused by exceptionally rare underlying malignancy, such as burned-out testicular tumor. Case presentation A 42-year-old man presented subacute progression of hearing loss and cerebellar ataxia. Cerebrospinal fluid showed continuous inflammation and magnetic resonance imaging (MRI) revealed cerebellar atrophy and hot cross-bun sign. Resection of tumors improved both laboratory findings and neurological signs and their pathology was seminoma. Conclusion Seminoma can cause PNS showing 8th cranial nerve palsy, cerebellar, and brainstem atrophy with hot cross-bun sign on MRI study. Extensive screening for onconeural antibodies was negative and thereby suggested that unknown antibodies worked for both antitumor immunity and induction of PNS.