Lymphomatosis cerebri: a rare diffuse leukoencephalopathy you should never miss.

INTRODUCTION: Lymphomatosis cerebri (LC) is a rare variant of primary central nervous system lymphoma that diffusely involves throughout the brain. In recent years, increasingly reported cases have notably broadened the spectrum of clinical and radiological features; however, it remains a great diagnostic challenge. CASE REPORT: We reported an atypical case of LC presented with subacute onset of focal neurological deficits and diffuse T2 hyperintensities without contrast enhancement on magnetic resonance imaging. He was initially considered as inflammatory leukoencephalopathy and received empirical corticosteroids, showing a dramatically clinical response. Three months later, the patient relapsed with deteriorating symptoms and enlarged brain lesions with mass-like enhancement. A diagnosis of LC was finally established according to the radiological and pathological findings. DISCUSSION: Though rare, LC should always be kept as a differential diagnosis of diffuse leukoencephalopathy. Neurologists should be aware of every detailed information about LC to avoid a delay of diagnostic biopsy in clinical practice.