Encephalopathy and severe neuropathy due to probable systemic vasculitis as an initial manifestation of mixed connective tissue disease.

We described a 69-year-old woman with neurological manifestations due to mixed connective tissue disease (MCTD). The patient demonstrated subacute cognitive decline, seizure and gait disturbance with no connective tissue manifestation. She had been diagnosed with dementia at another hospital, later in our hospital, serological examinations disclosed high titers of anti-RNP antibody. Cognitive dysfunction in this patient was dramatically ameliorated by steroid therapy. Three months later, she developed edema of the hands, synovitis and acrosclerosis. The patient was finally diagnosed as having MCTD. We emphasized MCTD as a rare cause of "treatable dementia".