Misdiagnosis of Behcet’s disease lung involvement as pulmonary cryptococcosis on imaging

RATIONALE: Behçet's disease (BD) is a systemic vasculitis that rarely involves the lungs. Pulmonary manifestations of BD can radiographically mimic infectious pneumonia, posing a substantial diagnostic challenge and increasing the risk of inappropriate treatment. This case report describes a young female patient with BD who presented with pulmonary opacities initially misdiagnosed as cryptococcal pneumonia based on imaging findings. PATIENT CONCERNS: A 28-year-old woman with a known history of BD presented with a 1-month history of fever, cough, and productive yellow sputum. She had been on long-term glucocorticoids, hydroxychloroquine, and colchicine for her underlying autoimmune disease. DIAGNOSIS: Chest computed tomography revealed bilateral consolidation and nodules with subsequent cavitation, initially suggestive of pulmonary cryptococcosis. However, extensive microbiological workup, including next-generation sequencing of blood and bronchoalveolar lavage fluid, failed to identify any pathogen. Computed tomography pulmonary angiography demonstrated microthrombi and arteritis, leading to the final diagnosis of pulmonary vasculitis secondary to BD. INTERVENTIONS: The patient was treated with methylprednisolone, which was gradually tapered, alongside supportive care. Antifungal and antibacterial therapies were discontinued after negative microbiological results were confirmed. OUTCOMES: The patient showed dramatic clinical improvement, with resolution of fever and respiratory symptoms. Follow-up computed tomography demonstrated significant regression of consolidation and complete resolution of cavitary lesions. At discharge, her laboratory parameters had normalized, and she remained stable during 1-year follow-up. LESSONS: This case underscores that in BD patients, pulmonary opacities mimicking infection on imaging should not be automatically attributed to opportunistic pathogens. When empirical anti-infective therapy fails, and microbiological evidence remains negative within 72 hours, clinicians should promptly consider pulmonary vasculitis and pursue vascular imaging. Early recognition and timely initiation of immunosuppressive therapy can be lifesaving.