Long-Term Survivor with Paraneoplastic Cerebellar Ataxia and Small-Cell Lung Cancer

<b>Background/Objectives:</b> Paraneoplastic cerebellar degeneration (PCD) is an inflammatory autoimmune process caused by onconeural antibodies directed against cerebellar Purkinje cells. In most cases, prognosis is poor as disease progression leads to pancerebellar dysfunction and permanent neurological damage. Through this case report, we aim to highlight the clinical presentation, diagnostic process, and therapeutic implications associated with PCD secondary to SCLC. <b>Methods:</b> Herein, we present the case of a 57-year-old patient diagnosed with PCD who presented with progressive limb ataxia and impaired mobility. CT scans and EBUS (endobronchial ultrasound) bronchoscopy established the diagnosis of limited-stage small-cell lung cancer (SCLC) of the right lung with marked lymphadenopathy. <b>Results:</b> Anti-CV2/CRMP5 and anti-SOX1 autoantibodies were identified in the serum that confirmed the diagnosis of PCD related to SCLC. A total of six cycles of chemotherapy with carboplatin and etoposide resulted in rapid clinical improvement and complete response of the disease. The patient remains in remission six years after the initial diagnosis with no neurological deficits. <b>Conclusions:</b> The prognosis of PCD greatly depends on early detection and management of the underlying malignancy. Despite the poor prognosis, early diagnosis and prompt initiation of chemotherapy may offer a great survival benefit in these patients.