Reversal of Cerebral Glucose Hypometabolism in a Patient with COVID and Refractory B-Cell Lymphoma.

Cerebral glucose hypometabolism (CGHM) involves reduced brain glucose uptake on FDG-PET imaging and occurs in neurological and systemic diseases. Its reversibility remains uncertain. We describe a 40-year-old man with reversible global CGHM associated with cryptogenic organizing pneumonia (COP) and COVID-19. His neurocognitive symptoms improved rapidly following steroid-induced hyperglycemia, with FDG-PET demonstrating complete CGHM resolution after two months. His medical background included primary refractory transformed follicular lymphoma diagnosed 30 months earlier, managed with multiple treatment regimens including CAR-T therapy. After post-CAR-T relapse, combination therapy with polatuzumab vendotin, bendamustine, and obinutuzumab achieved complete remission, which was maintained when CGHM developed. This case establishes that CGHM can be temporary and reversible, highlighting a previously unrecognized pathway through which systemic illness may produce neurocognitive impairment. The rapid cognitive recovery coinciding with steroid-induced hyperglycemia and COP treatment is significant. Additional investigation is warranted to determine CGHM's significance in diverse pathological conditions and determine therapeutic interventions.