Abstract
BACKGROUND
Diffuse leptomeningeal glioneuronal tumors (DLGNT) are rare central nervous system tumors first described in the 2016 WHO classification. A paucity of data exists on this tumor. This case describes an adult presentation of DLGNT, a classically pediatric tumor, and highlights the importance of genetic and epigenetic analyses in neuro-oncologic diagnoses. CASE: A 22-year-old male presented with shoulder paresthesias and back pain, progressing to bilateral leg weakness. Spine MRI demonstrated an enhancing intramedullary T8 lesion, prompting urgent laminectomy and resection. Frozen section suggested a glial neoplasm. Four-month follow-up MRI spine showed leptomeningeal dissemination at the C-spine and caudal thecal sac. CSF analysis revealed 110 mg/dL protein, 2 cells/mcl, and negative cytology. NCI methylation profiling demonstrated 1p deletion and KIAA1549:BRAF fusion, consistent with DLGNT, subtype 1, with MAPK pathway activation; Ki-67 index was 30%. Treatment with binimetinib was initiated. After 1 month of therapy, the patient is tolerating treatment and strength is improving.
DISCUSSION
This case describes a rare presentation of a rare tumor. DLGNT, subtype 1, has a median age of diagnosis of 5 years and an indolent course. We describe an adult patient with molecular features consistent with DLGNT subtype 1, but a high proliferative index suggesting a more aggressive growth potential. In this case, methylation profiling aided in diagnosing the tumor type and guided treatment. The KIAA1549:BRAF fusion is an activating mutation in the MAPK pathway, and binimetinib was selected as a MEK inhibitor with high CNS penetration. To our knowledge, this is the first case of an adult-onset DLGNT treated with binimetinib. Based on our single patient experience, we would advocate for methylation profiling for rare CNS tumor entities.