[Acute relapsing disseminated encephalomyelitis (ARDEM) mimicking a temporal lobe tumor].

A case of ARDEM presenting as a temporal lobe tumor is reported. A 19-year-old male was admitted to the hospital, because of headache, right homonymous hemianopsia, and general convulsion. CT scan and MR imaging revealed localized right medial temporal enhanced mass lesion with surrounding brain edema. The craniotomy revealed an elastic hard ill-defined subcortical tumor. Histology showed a demyelinating process with perivascular lymphocyte cuffings. The patients' postoperative course was essentially uneventful until the 7th day when he developed fever, persistent hiccup, vertigo followed by obtundation and respiratory distress. Repeated MR imaging revealed extensive lesions in the left thalamus, brain stem, upper spinal cord and cerebellum. The patient responded to steroid pulse therapy well. Six months later, however, he returned to the hospital with severe memory disturbance. Repeated MR imaging showed diffuse bilateral parieto-occipital white matter lesions. He again responded to steroid pulse therapy well. An immunosuppressant Mizoribine was added to his steroid therapy to prevent recurrence. With the advent of MR imaging, more non-surgical diseases such as multiple sclerosis and Behçet disease are visualized on imaging study. The differentiation of these diseases from intraparenchymal neoplasm is difficult when they present as a single mass lesion. ADEM or ARDEM should be included in the list of such lesions requiring differential diagnosis.