Uncovering the Unusual: A Case of Mixed Connective Tissue Disease With Rare Presentation, Atypical Complications, and Therapeutic Dilemmas.

Mixed connective tissue disease (MCTD) is an overlap syndrome characterized by features of systemic lupus erythematosus, scleroderma, and polymyositis, along with the presence of the U1RNP antibody. A 46-year-old female patient presented with severe anemia, cough, and breathlessness, and was diagnosed with cold agglutinin disease, a type of autoimmune hemolytic anemia (AIHA). Autoimmune workup revealed MCTD by positive antinuclear and U1RNP antibodies. She had bilateral miliary mottling on X-ray and a tree-in-bud appearance on high-resolution computed tomography of the thorax, which were suggestive of pulmonary tuberculosis. Standard therapy with steroids was not advisable. She was subsequently started on anti-tuberculosis treatment (anti-Koch's therapy), followed by steroid therapy and immunosuppressive therapy after three weeks. The patient responded well to treatment, but after two months, she developed cytomegalovirus (CMV) retinitis. Adult-onset CMV disease may occur as a result of primary infection, reinfection, or activation of a latent infection. Although not directly related, it can occur as an atypical association in the setting of immunosuppressive therapy. Morbidity and mortality are significantly increased in this population secondary to infectious potentiation: immunosuppression causes infections, and infections cause AIHA. The management of MCTD and secondary AIHA and immunosuppression poses a therapeutic challenge.