Background <p>Subacute progressive cerebellar ataxia poses a diagnostic challenge due to its wide-ranging etiologies and symptom overlap with acute and chronic cerebellar disorders. Prompt identification and treatment are essential to improve clinical outcomes.</p> Case Presentation <p>A 62-year-old woman presented with worsening vertigo, gait instability, and evolving neurological signs over five months, consistent with a syndrome of subacute progressive cerebellar ataxia. Despite normal findings on serial MRI and PET imaging, as well as negative serological and genetic testing, her recent history of influenza vaccination and clinical progression suggested immune-mediated cerebellitis. High-dose corticosteroid therapy resulted in marked improvement, allowing her to achieve near-complete recovery, with a final diagnosis of autoimmune cerebellar ataxia reached by exclusion.</p> Discussion <p>Even when imaging findings are unremarkable, it is crucial to recognize immune-mediated cerebellar ataxia in patients with progressive symptoms, particularly following potential triggers such as vaccination. Empirical corticosteroid therapy demonstrated both diagnostic and therapeutic value, facilitating recovery.</p> Conclusion <p>Subacute cerebellar ataxia with normal imaging requires careful consideration of immune-mediated etiologies. This case demonstrates the potential benefits of corticosteroid therapy in achieving favorable outcomes, even in diagnostically challenging scenarios.</p>