Case Report: Secukinumab Experience in a Patient With Coexistence of Systemic Lupus Erythematosus, Ankylosing Spondylitis, and Antiphospholipid Antibody Syndrome.

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease characterized by autoantibody production and immune complex deposition. Antiphospholipid syndrome (APS) is frequently associated with SLE and is characterized by arterial or venous thrombosis and pregnancy morbidity in the presence of persistent antiphospholipid antibodies. The coexistence of ankylosing spondylitis (AS) with SLE and APS is extremely rare. A 38-year-old woman was admitted to our clinic with gangrene of the right fifth toe and swelling of both knees. She had a previous diagnosis of AS based on inflammatory low back pain and radiographic evidence of bilateral Grade 4 sacroiliitis. Laboratory investigations revealed positive antinuclear antibody, anti-double-stranded DNA, and antiphospholipid antibodies, including lupus anticoagulant and anti-cardiolipin IgG. Renal biopsy performed due to proteinuria demonstrated mesangioproliferative lupus nephritis. Based on clinical, laboratory, and histopathological findings, the patient was diagnosed with coexisting AS, SLE, and APS. Considering the coexistence of these autoimmune diseases and the patient's previous exposure to anti-tumor necrosis factor therapy, treatment with the interleukin-17 inhibitor secukinumab was initiated. The patient showed significant improvement in inflammatory back pain and arthritis during follow-up. To our knowledge, this is one of the rare reported cases of coexistence of AS, SLE, and APS treated with secukinumab.