Atypical STING-Vasculopathy Phenotype: Definite Usual Interstitial Pneumonia (UIP)-Pattern CT With Mixed Fibrotic Histology: A Case Report.

STING‑associated vasculopathy with onset in infancy (SAVI) is a rare autoinflammatory disorder that causes systemic inflammation, vasculopathy, and progressive interstitial lung disease (ILD). The pulmonary manifestations of SAVI typically resemble a nonspecific interstitial pneumonia (NSIP) pattern both radiologically and histologically. We present a case of a 20‑year‑old male with genetically confirmed SAVI who developed acute hypoxic respiratory failure triggered by respiratory syncytial virus infection, despite appropriate treatment. Imaging revealed extensive subpleural fibrosis, traction bronchiectasis, and honeycombing. These findings were observed in the setting of a CT appearance strongly consistent with a definite usual interstitial pneumonia (UIP) pattern. Ultimately, the patient underwent a lung transplant, and histopathology of the explanted lungs revealed fibrotic changes, including diffuse interstitial thickening, lymphoid aggregates, and honeycombing, without definitive fibroblastic foci, indicating a mixed UIP and NSIP pattern of fibrosis. This case illustrates a rare UIP‑pattern imaging phenotype in SAVI‑associated ILD, despite a mixed UIP‑NSIP histologic pattern of pulmonary fibrosis, and highlights the potential for acute viral infection to precipitate decompensation in patients with interferon‑driven pulmonary fibrosis. Written informed consent was obtained from the patient for publication of this report and accompanying images.