Coexistence of anti-synthetase syndrome and Behçet’s disease complicated by Pneumocystis jirovecii pneumonia and pulmonary embolism: a case report and literature review

Anti-synthetase syndrome (ASS) is a rare systemic autoimmune disorder characterized by the presence of anti-aminoacyl-tRNA synthetase (ARS) antibodies and various clinical manifestations such as myositis, arthritis, and interstitial lung disease (ILD). Behçet’s disease (BD) is a chronic, relapsing, multisystemic vasculitis that can involve arteries and veins of all calibers. The coexistence of ASS and BD has never been reported previously, and their concurrent presentation poses significant diagnostic and therapeutic challenges. We report the case of a 49-year-old man presenting with recurrent fever, cough, and dyspnea for over one month. Chest computed tomography (CT) revealed bilateral diffuse infiltrates, and targeted next-generation sequencing (tNGS) of bronchoalveolar lavage fluid identified Pneumocystis jirovecii, cytomegalovirus, and Epstein–Barr virus. The patient developed acute pulmonary embolism and lower limb deep venous thrombosis during hospitalization. Serological testing showed positivity for anti-PL-12 antibodies and HLA-B51. Based on the presence of mechanic’s hands, interstitial lung disease, and anti-PL-12 antibody positivity, a diagnosis of ASS was established. The patient also met the International Criteria for Behçet’s Disease (ICBD), with recurrent oral and genital ulcers, pseudofolliculitis, and venous thrombosis, leading to a concurrent diagnosis of BD. He was treated with prednisone, mycophenolate mofetil, hydroxychloroquine, and anticoagulation, combined with antimicrobial therapy and multidisciplinary management. After one month of therapy, pulmonary infiltrates and thromboses had significantly resolved, and mucocutaneous lesions improved markedly. This is the first reported case of anti-synthetase syndrome coexisting with Behçet’s disease. This case underscores the importance of considering overlapping autoimmune disorders in patients who present with complex multisystem involvement. Early recognition and the implementation of individualized immunosuppressive therapy through multidisciplinary collaboration may lead to favorable clinical outcomes, even in such rare and challenging presentations.