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DLCO Decline in SSc — SCE Rheumatology MCQ

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HardSystemic SclerosisDLCO Decline in SScSCE Rheumatology

A 48-year-old woman with systemic sclerosis develops progressive exertional breathlessness. Over 12 months, her FVC has remained stable at 80% predicted, whereas her DLCO has fallen from 65% to 42% predicted, giving an FVC/DLCO ratio of 1.90. Repeat testing meets quality-control standards and the DLCO values are corrected for haemoglobin, which is normal. Comparative HRCT shows unchanged minimal interstitial abnormality and no emphysema. What is the most likely explanation for this pulmonary function pattern?

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Correct answer: A — Developing systemic sclerosis-associated pulmonary arterial hypertension

The best answer is A. In systemic sclerosis, a marked and reproducible fall in DLCO that is disproportionate to FVC, particularly with an increasing FVC/DLCO ratio and little HRCT-defined ILD, is a pulmonary vascular warning pattern and should prompt evaluation for pulmonary hypertension. Serial UK cohort data show that DLCO decline and change in the FVC/DLCO ratio accelerate before pulmonary hypertension is diagnosed. This pattern is suggestive rather than diagnostic: echocardiography, biomarkers and an appropriate screening pathway should follow, with right heart catheterisation required to confirm and classify pulmonary hypertension. Anaemia and technical error have been excluded by haemoglobin correction and repeat quality-controlled testing. Progressive ILD would more usually produce radiological progression and declining lung volumes. A fall of this magnitude is not normal variation.

Reference: Nihtyanova SI et al. Dynamic Prediction of Pulmonary Hypertension in Systemic Sclerosis Using Landmark Analysis. Arthritis & Rheumatology. 2023;75:449-458. https://pubmed.ncbi.nlm.nih.gov/36122180/