Bilateral Paraneoplastic Optic Neuropathy as the First Presentation of Preclinical Small Cell Lung Cancer: Case Report.

Introduction: Paraneoplastic optic neuropathy (PON) is a rare immune-mediated optic neuropathy, secondary to an underlying malignancy. This report describes a rare case of bilateral PON as the initial manifestation in a 77-year-old male, leading to the early detection and treatment of preclinical small cell lung cancer (SCLC). Case Presentation: The patient initially presented with incidental bilateral disc swelling but was asymptomatic, with preserved visual function. Initial investigations, including orbito-cranial imaging, lumbar puncture, temporal artery ultrasound, and serological testing, were inconclusive. Six weeks later, the patient had persistent disc swelling with compromised bilateral visual function and was commenced on oral steroids. Further diagnostic workup identified paraneoplastic antibodies (anti-CV2/CRMP-5 and anti-Hu) and PET scan findings consistent with a nodular SCLC. Following biopsy confirmation, the patient underwent carboplatin and etoposide chemotherapy, followed by radiotherapy. Initial oral steroids, prior to cancer treatment, resulted in resolution of optic disc swelling and stabilization of visual function. Conclusion: This case underscores the importance of a systematic approach to optic neuropathies where an initial diagnosis is not found, revisiting diagnostic pathways when initial findings remain ambiguous, and consideration of PON as a differential - even in the absence of known malignancy or typical cancer symptoms. Timely recognition allows for early intervention, improving patient outcomes. This report contributes to the limited literature on PON and highlights the role of multidisciplinary care in managing complex cases involving paraneoplastic syndromes.