Anti-Zic4 Paraneoplastic Cerebellar Degeneration With Mesial Temporal Lobe Hyperintensity in a Patient With Papillary Thyroid Carcinoma: A Case Report and Review of the Literature.

Paraneoplastic cerebellar degeneration (PCD), a subtype of paraneoplastic neurological syndromes (PNSs), is a rare autoimmune neurologic syndrome that usually develops secondary to an underlying malignancy. We present a 49-year-old patient that developed PCD secondary to occult papillary thyroid carcinoma. The patient had progressive difficulty ambulating for 3 years. A neurological exam revealed signs of cerebellar syndrome. Brain magnetic resonance imaging (MRI) showed significant cerebellar atrophy and mesial temporal lobe hyperintensity. Immunological testing was highly positive for anti-CV2 and anti-Zic4 onconeural antibodies. Positron emission tomography (PET)/Computerized tomography (CT) scan revealed significant hypermetabolic uptake of F-18 fluorodeoxyglucose (FGD) by a left thyroid nodule. Histological examination of the nodule was positive for papillary thyroid carcinoma, confirming the diagnosis of PCD. A trial of high-dose methylprednisolone failed to improve the patient's symptoms. This case highlights the importance of maintaining high suspicion for PCD while investigating cases of cerebellar degeneration. Early detection is essential to prevent irreversible damage in affected patients.