Paraneoplastic cerebellar degeneration (PCD) is characterized by a subacute, severe pancerebellar syndrome, which is related to an underlying tumor. The presence of CSF or serum onconeural antibodies confirms the diagnosis and indicates the underlying tumor type. However, the association between PCD and extragonadal germ cell tumors with the absence of an onconeural antibody has rarely been described. We present a 55-year-old man who developed a pancerebellar syndrome, which made him unable to walk alone after 10months. Routine blood analysis, brain MRI and CSF examination were normal. Despite onconeural antibodies were negative, a whole body PET-CT scan showed a hypermetabolic nodule in the thymus, which was removed, and a hypometabolic presacral mass. The pathologic study revealed a germinoma surrounded by a pronounced inflammatory infiltrate. Shortly after, the patient clearly improved his symptoms, before receiving chemotherapy and prednisone. The cerebellar ataxia worsened when steroids were reduced below 30mg/day. Testicular sonography showed a suspicious lesion in one testicle, but no malignancy was found after orchiectomy. The presacral mass was removed after chemotherapy disclosing a mature teratoma. Our patient emphasizes that despite the absence of onconeural antibodies, studies to rule out an underlying tumor are mandatory in patients with subacute cerebellar ataxia.
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