Isolated Small Fiber Neuropathy and Chemotherapy-Associated Cognitive Dysfunction Following Treatment for Gastric Adenocarcinoma: A Case Report of a Unique Entity.

Small fiber neuropathy (SFN) is a poorly documented complication in oncology patients and is often overlooked due to a lack of awareness and testing. Concurrent chemotherapy-induced cognitive impairment ("chemobrain") adds diagnostic complexity. We present a rare case of a 44-year-old male who developed SFN with intact large fibers, along with progressive cognitive slowing after completing neoadjuvant and adjuvant chemotherapy for gastric adenocarcinoma. Despite normal nerve conduction and brain MRI, the patient's autonomic testing displayed severely abnormal sudomotor and microcirculatory responses. This report underscores the need for awareness of selective small fiber damage and neurotoxicity in cancer survivors while highlighting the diagnostic value of autonomic and sweat-based evaluations in unexplained peripheral symptoms post-chemotherapy.