33-year-old woman with mixed connective tissue disease and rapid onset breathlessness

We present a 33-year-old woman with anti-U1 ribonucleoprotein antibody positive mixed connective tissue disease (MCTD) since the age of 13. Predominant features were of inflammatory arthritis, Raynaud’s phenomenon and fatigue. She had been stable on combined methotrexate and hydroxychloroquine. She presented acutely in 2022 with breathlessness and sudden onset chest pain. Clinical examination revealed reduced air entry bibasally but was otherwise unremarkable. C-reactive protein (CRP) and double-stranded DNA were raised (46 mg/L and 26 IU/L) with normal complement. CT pulmonary angiogram (CTPA) excluded pulmonary emboli but revealed small bilateral effusions and a 3 cm pericardial effusion confirmed on subsequent echocardiogram. She received a tapering course of prednisolone to continue on 10 mg with initial improvement. She re-presented 5 months later with progressive breathlessness over weeks, particularly when lying flat. There were no clinical symptoms or signs suggestive of connective tissue disease flare or active infection. Lung function testing demonstrated reduced forced vital capacity (FVC) of 1.72 L (46% predicted) with a ratio of 79.7. The diffusing capacity of the lungs for carbon monoxide (TLCO) was reduced (59.6% predicted) but correctable (carbon monoxide transfer coefficient (KCO) 108.9%), in keeping with a rapidly progressive restrictive pathology (figure 1) for which she was admitted for inpatient investigation. CRP was elevated (74 mg/L) with lymphopenia (0.53 109/L). N-terminal pro B-type natriuretic peptide (NT-pro BNP), …