Overlap Syndrome of Ankylosing Spondylitis and Mixed Connective Tissue Disease in a Male Patient

Spondyloarthritis (SPA) is a chronic systemic inflammatory disease predominantly affecting young men, with axial and peripheral involvement and extra-articular manifestations, including uveitis, inflammatory bowel disease, and psoriasis. Mixed connective tissue disease (MCTD) is a rare, heterogeneous autoimmune disorder primarily affecting women of reproductive age. It is characterized by circulating autoantibodies leading to immune-mediated inflammation and progressive tissue damage. The coexistence of these two conditions is rarely reported in the literature. The present study reports the case of a 25-year-old male patient who had ankylosing spondylitis (AS) for four years and had been receiving diclofenac for six months, followed by ketoprofen at a dose of 150 mg/day and sulfasalazine at 2 g daily. The patient presented with severe pain and high disease activity after three years of remission under treatment. Immunological testing revealed positivity for anti-U1 RNP antibodies (11 UA). Based on these findings, a diagnosis of MCTD was established. The patient received high-dose intravenous corticosteroid therapy, with a significant clinical and biological response.