Brain involvement by leprosy presenting as a frontal cystic lesion.

Leprosy has a predilection for peripheral nerves and is not considered to involve the CNS. The idea that the CNS is exempt from Mycobacterium leprae bacilli has been suspected from a clinical perspective or CSF study in leprosy patients. However, there has been no direct evidence for CNS involvement by leprosy in a living patient. To the best of the authors' knowledge, the present case is the first report providing histopathological and molecular evidence for CNS involvement by leprosy in a living patient. Brain MRI revealed a 2-cm cystic lesion in the right frontal lobe of the patient. The medical history revealed that the patient had been receiving multidrug therapy for borderline lepromatous leprosy. Neuronavigation-guided craniotomy and lesion removal were performed due to a presumptive diagnosis of low-grade glioma. The brain specimen demonstrated variably thickened blood vessels and densely scattered foamy macrophages in the perivascular spaces and parenchymal stroma. Fite acid-fast stain displayed red granular inclusions that were suggestive for fragmented M. leprae. M. leprae-specific nested polymerase chain reaction amplification showed positive bands, and DNA sequencing also demonstrated homology with the M. leprae genome. This case supports the notion that M. leprae can involve the cerebral cortex regardless of cranial nerve engagement.