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SSc FVC DLCO Ratio — SCE Rheumatology MCQ

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HardSystemic SclerosisSSc FVC DLCO RatioSCE Rheumatology

A 65-year-old woman with systemic sclerosis and limited, radiologically stable interstitial lung disease develops progressive exertional dyspnoea and a dry cough. Her haemoglobin is normal. Pulmonary function tests show an FVC of 76% predicted and a haemoglobin-corrected DLCO of 44% predicted, giving an FVC/DLCO ratio of 1.73. Which additional pathological process should this pattern particularly raise suspicion for?

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Correct answer: E — Coexistent pulmonary vascular disease, including pulmonary arterial hypertension

The correct answer is E. In systemic sclerosis, a disproportionately reduced DLCO relative to FVC—particularly an FVC/DLCO ratio above approximately 1.6—raises suspicion of pulmonary vascular disease, including SSc-associated pulmonary arterial hypertension. It is a screening signal rather than a diagnostic criterion and should prompt structured assessment with echocardiography, NT-proBNP and an appropriate screening algorithm; right heart catheterisation confirms pulmonary hypertension when indicated. Progressing ILD generally produces a more proportionate restrictive defect and is less likely here because the HRCT appearances are stable. Obesity predominantly reduces lung volumes rather than causing this pattern. Normal ageing does not adequately explain the severity of DLCO reduction. Anaemia can lower DLCO, but haemoglobin is normal and the reported DLCO is haemoglobin-corrected.

Reference: Nihtyanova SI et al. Dynamic Prediction of Pulmonary Hypertension in Systemic Sclerosis Using Landmark Analysis. Arthritis & Rheumatology. 2022. https://pubmed.ncbi.nlm.nih.gov/36122180/