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Isolated Low DLCO Significance — SCE Rheumatology MCQ

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ModerateMusculoskeletal ImagingIsolated Low DLCO SignificanceSCE Rheumatology

A 60-year-old woman with seropositive rheumatoid arthritis has taken a stable dose of methotrexate for 5 years. She develops a persistent dry cough without fever or acute systemic illness. She has never smoked and her haemoglobin is normal. Spirometry and lung volumes are normal, with an FVC of 85% predicted and a normal FEV1/FVC ratio, but haemoglobin-corrected DLCO is 58% predicted. Which interpretation is most appropriate?

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Correct answer: B — The result may be an early marker of RA-associated interstitial lung disease despite preserved FVC, and HRCT chest is appropriate

Explanation lettering: C = shown as A · E = shown as B · A = shown as C · B = shown as E

E is correct. A haemoglobin-corrected DLCO of 58% predicted is clinically abnormal. In RA-associated ILD, impaired gas transfer may be detectable while FVC and other lung volumes remain preserved; persistent cough increases the need to investigate. HRCT is therefore appropriate to identify and characterise ILD or another RA-related pulmonary abnormality. An isolated low DLCO is not specific for ILD and can also occur with pulmonary vascular disease, emphysema or anaemia, but the latter two are made less likely here. A threshold below 40% denotes severe impairment rather than the point at which DLCO first becomes significant. DLCO is relevant outside systemic sclerosis and is not rendered unreliable by methotrexate treatment. An unexplained reduction should not be dismissed as normal ageing.

Reference: Antoniou KM et al. ERS/EULAR clinical practice guidelines for connective tissue disease-associated interstitial lung disease, RA screening and diagnostic work-up algorithms, 2025. https://pubmed.ncbi.nlm.nih.gov/40907995/