Abstract
OBJECTIVE: Interstitial lung diseases (ILDs) comprise a heterogeneous group of disorders characterized by inflammation and fibrosis of the pulmonary interstitium, posing significant challenges in identifying their underlying causes. Pneumocystis pneumonia (PCP) is the leading cause of ILD in people living with HIV (PLWH). In individuals with connective tissue diseases, ILD is a frequent complication with significant morbidity and mortality. METHODS: A case is presented that details the intricate diagnostic process of rapidly progressive interstitial lung disease (RP-ILD). RESULTS: The patient initially presented with clinical features consistent with ILD, including progressive respiratory symptoms and radiological findings typical of pulmonary inflammation. Coupled with a positive HIV screening result, these findings led to an initial misdiagnosis of PCP, a common opportunistic infection in PLWH. However, despite standard anti-PCP treatment, the patient's condition did not improve, prompting further diagnostic evaluations. Subsequent investigations revealed the presence of serum anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibody, a biomarker strongly associated with rapidly progressive ILD in clinically amyopathic dermatomyositis (CADM). CONCLUSION: This case report offers a novel perspective on the diagnostic process of ILD, particularly emphasizing the importance of distinguishing false-positive antibodies caused by autoimmune diseases in the context of positive HIV screening tests, thereby improving the accuracy of RP-ILD diagnosis and mitigating the mortality burden associated with this condition.