Primary lymphoma of the central nervous system: a diagnostic problem.

Primary lymphoma of the central nervous system (CNS) is difficult to diagnose because of the difficulty in differentiating it from multiple sclerosis, sarcoidosis, metastatic disease, chronic granulomatous disease, and cerebral cysticercosis. With the patient presented in this report, no abnormalities were found after performing laboratory tests, using radiographic modalities, and taking biopsies. Dexamethasone treatment was initiated, and patient's symptoms improved.Primary CNS lymphoma was not diagnosed until a year after presentation, due to lack of tissue diagnosis. CNS must be suspected when a diagnosed tumor treated with steroid is not found at surgery. It is suggested that a computerized tomographic scan be requested before the start of steroid therapy, as the lesion can disappear with steroid treatment.