RESUMEN
BACKGROUND: Primary central nervous system lymphoma is rare, and primary central nervous system T cell lymphoma is relatively uncommon, contributing to < 5% of all cases. Lymphomatosis cerebri, a rare subtype of primary central nervous system lymphoma, is characterized by extensive white-matter lesions on magnetic resonance imaging and nonspecific symptoms, such as cognitive decline and depression. Reports of lymphomatosis cerebri in adult T cell leukemia/lymphoma are limited. CASE PRESENTATION: A 49-year-old Japanese man gradually developed insomnia, anorexia, and weight loss over a 2-month period following work-related promotion. Initially diagnosed with depression, his condition rapidly deteriorated with cognitive decline and motor dysfunction. Despite various treatments, his symptoms persisted within a month. Upon admission, the presence of neurological abnormalities suggestive of a central nervous system disorder raised suspicion of a cerebral lesion. Diagnostic tests revealed extensive brain lesions on imaging and the presence of atypical lymphocytes (flower cells) in the cerebrospinal fluid. The patient was diagnosed with lymphomatosis cerebri due to adult T cell leukemia/lymphoma, a rare presentation in the literature. Due to irreversible brainstem damage and poor neurological prognosis, aggressive treatment was not initiated, and the patient died, with an autopsy confirming the diagnosis. CONCLUSION: Lymphomatosis cerebri with adult T cell leukemia/lymphoma is very rare. It is crucial to promptly consider lymphomatosis cerebri as a differential diagnosis, particularly in cases of rapid cognitive decline and poor treatment response. Recognition of lymphomatosis cerebri as an important differential diagnosis for cognitive decline, and depression is necessary for timely intervention and management. Further research is required to better understand this unique and rare presentation in adult T cell leukemia/lymphoma.