Diagnostic challenges in an adult patient with Fanconi Anemia: Neuroinflammatory Syndrome (FANS) intertwined with infectious processes.

Fanconi Anemia (FA) is a rare genetic disorder characterized by bone marrow failure and an increased risk of malignancies. Neuroinflammatory presentations in adulthood are exceedingly rare and pose profound diagnostic challenges, particularly when atypical neurological manifestations closely mimic opportunistic central nervous system infections in an immunocompromised host. We present the complex case of a 32-year-old male with FA who developed a progressive neuroinflammatory syndrome intertwined with infectious processes. The patient presented with fatigue, fever, altered mental status, and gait instability. Initial magnetic resonance imaging (MRI) revealed peripheral enhancing lesions and scattered millimetric calcifications within the cerebrum and cerebellum, clearly delineated on susceptibility-weighted imaging (SWI). Concurrently, a positive CMV PCR raised high suspicion for an opportunistic viral encephalitis, prompting empirical antiviral, antifungal, and broad-spectrum antibiotic therapies. A follow-up contrast-enhanced brain MRI at six weeks demonstrated stability of the lesions. Because severe thrombocytopenia precluded a stereotactic brain biopsy, histopathological confirmation was unavailable. However, the lack of radiological progression argued against an untreated aggressive infectious or neoplastic etiology. While a partially treated opportunistic infection or healed granulomatous disease cannot be definitively excluded, the overall clinical and radiological findings were favored to represent Fanconi Anemia Neurologic Syndrome (FANS). This case highlights the extraordinary diagnostic dilemma of differentiating primary neuroinflammatory syndromes from opportunistic infections in adult patients with FA. Furthermore, it emphasizes the indispensable role of advanced MRI sequences, such as SWI, and longitudinal radiological follow-up in evaluating suspected non-infectious neurological involvement when tissue diagnosis is clinically contraindicated.