Cancer-Associated Retinopathy Presenting with Paraneoplastic Cerebellar Degeneration in Tonsillar Squamous Cell Carcinoma: A Case Report

Background and Clinical Significance: Cancer-associated retinopathy (CAR) is a rare paraneoplastic autoimmune retinopathy caused by antibodies targeting tumor antigens with cross-reactivity to retinal proteins. Paraneoplastic cerebellar degeneration (PCD) results from autoimmune injury to cerebellar tissue triggered by onconeural antigens. We report a rare case of CAR occurring concurrently with seronegative PCD in a patient with poorly differentiated tonsillar squamous cell carcinoma, and we describe the long-term sequelae of CAR-related macular atrophy; Case Presentation: A 66-year-old male presented with progressive painless bilateral peripheral and night vision loss, truncal ataxia, dysmetria, and dysarthria. Optical coherence tomography demonstrated diffuse outer retinal loss, and multifocal electroretinography showed markedly reduced responses bilaterally. Evaluation revealed poorly differentiated squamous cell carcinoma of the right tonsil. CAR antibody testing was positive for recoverin, enolase, and carbonic anhydrase II antibodies. Brain MRI demonstrated cerebellar atrophy. After exclusion of other autoimmune etiologies, he was diagnosed with seronegative PCD. Treatment included robotic tonsillectomy with neck dissection, intravenous immunoglobulin, high-dose corticosteroids, and maintenance rituximab. At 6 months, visual acuity, color vision, and electro-retinography improved. Seven years later, he remains independent in activities of daily living despite the progression of retinal atrophy and cerebellar dysfunction; Conclusions: This case highlights the rare coexistence of CAR and seronegative PCD associated with tonsillar squamous cell carcinoma. Multimodal oncologic and immunosuppressive therapy produced meaningful neurologic and visual improvement, despite progressive long-term retinal degeneration.