Subtle lung lesion in a middle-aged woman with fever and cough

A 45-year-old woman had a history of rheumatoid arthritis under medical control with independent daily activity. She presented with fever (38.5°C), dry cough and dyspnoea on exertion for 5 days, accompanied with intermittent headache. Chest X-ray and CT scan both showed clear lung fields, so she was treated as upper airway infection. However, the symptoms persisted on and off for 6 months. Laboratory data on follow-up showed thrombocytopenia (54 000/µL) and lymphopenia (2.7%). A repeated chest CT scan showed fibronodular lesions and linear atelectasis (figure 1A). Empirical antibiotics failed, so interstitial lung disease or atypical infection was suspected. A wedge biopsy of the lung was performed. Figure 1 (A) Axial image of non-contrast chest CT (5 mm thickness) using lung window setting reveals ill-defined part-solid ground-glass opacity (GGO) and nodular interlobular septal thickening (ILST, white arrows) in the left lower lobe (LLL). A magnified coronal chest CT image shows another subpleural GGO and ILST in LLL (white arrowheads). (B) The lung biopsy shows open alveolar spaces with interstitial widening. In high-power field, the capillaries in thickened septa contain large atypical cells with moderate amount of cytoplasm and round or oval vesicular nuclei with large prominent nucleoli (B inset). (C–D) Immunohistochemically, these atypical cells are positive for …