Mixed Connective Tissue Disease (MCTD): A Rare Presentation of Probable Central Nervous System (CNS) Vasculitis

Mixed connective tissue disease (MCTD) may rarely involve the central nervous system (CNS), and CNS vasculitis can present with acute seizures, altered consciousness, and focal neurological deficits. We report a 27-year-old woman with a seven-year history of arthralgia, morning stiffness, intermittent fever, and malaise who developed acute seizures, altered sensorium, and hemiparesis approximately two weeks before hospital admission. Laboratory evaluation demonstrated severe anemia, thrombocytopenia, elevated inflammatory markers, and positive anti-U1 ribonucleoprotein (U1-RNP) antibodies. Cerebrospinal fluid (CSF) showed lymphocyte-predominant pleocytosis and markedly elevated protein, while brain MRI demonstrated multifocal confluent subcortical and periventricular lesions with restricted diffusion. Based on clinical, serological, CSF, and neuroimaging findings, MCTD-associated CNS vasculitis was considered probable. The patient received broad-spectrum antibiotics and antiseizure and antihypertensive therapy, followed by methylprednisolone pulses, oral prednisolone, and hydroxychloroquine, with significant neurological improvement at discharge. Cyclophosphamide therapy was planned; however, no subsequent follow-up data were available. This case emphasizes the need to consider CNS involvement in patients with MCTD while recognizing the limitations of imaging specificity and incomplete long-term follow-up.