Primary central nervous system ALK positive anaplastic large cell lymphoma with predominantly leptomeningeal involvement in an adult.

A 31-year-old Korean male presented with altered consciousness and severe headache. Brain MRI delineated focal leptomeningeal enhancement without any intracerebral lesions. Diagnosis was made based on a brain biopsy showing anaplastic large cell lymphoma (ALCL), immunohistochemical stains revealing positivity for anaplastic lymphoma kinase (ALK) and an absence of involvement in any other organs; specifically, the primary central nervous system ALK+ALCL. Complete remission was achieved following 5 cycles of systemic chemotherapy with a high dose of Methotrexate and a simultaneous 7 cycles of intrathecal triple chemotherapy. Diagnosis of primary leptomeningeal ALK+ALCL is challenging given its rarity and non-specific symptoms along with non-pathognomonic radiologic findings. We present the first case of primary leptomeningeal ALK-positive ALCL where the clinical course, pathologic characteristics and treatment modality are described as well as a review of literature.