Clinical Immunology and Rheumatology Services, Department of Medicine, All India Institute of Medical Sciences, New Delhi, India
Correspondence to: R. Gupta, Clinical Immunology and Rheumatology Services, Department of Medicine, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India. E-mail: guptarajiva{at}hotmail.com
SIR, I read the article by Mukerjee et al. [1] with much interest and also read their earlier article [2] on a related topic. I do agree that we need a reliable and cheap screening test for scleroderma patients suspected to have pulmonary arterial hypertension. Unfortunately, the gold standard of cardiac catheterization cannot be used as a screening test as it is invasive and not easily available. Similarly, although echocardiography is non-invasive and reliable, as shown in the study by this author, it is difficult to have available for all patients. But all these patients have a pulmonary function test (PFT) as their routine work-up. We can screen the patient using PFT for isolated pulmonary hypertension. Mukerjee et al. used the diffusion capacity of the lung (DLCO) to correlate with pulmonary artery hypertension, with poor results. This finding was not surprising as DLCO will be reduced in interstitial lung disease (ILD), which is much more common than pulmonary arterial hypertension in scleroderma patients.
I feel that if we look at diffusion capacity (DLCO) in relation to the forced vital capacity (FVC) of the lungs the correlation may be more meaningful. As we know, in ILD both FVC and DLCO fall and their fall is proportionate, whereas in pulmonary arterial hypertension DLCO falls significantly and disproportionately to FVC. So if one considers the ratio FVC%/DLCO% in predicting pulmonary arterial hypertension, the chance of correlation with the cardiac catheterization diagnosis is better (FVC% patients FVC/predicted FVC x 100, DLCO% patients DLCO/predicted DLCO x 100).
I feel that if the FVC%/DLCO% ratio is more than 2 the chance of pulmonary arterial hypertension is very high and one should do cardiac catheterization or echocardiography to confirm it. If the ratio is less than 1.4 the chance of ILD is high and one should investigate by HRCT of the chest and avoid unnecessary echocardiography or cardiac catheterization. Values between 1.4 and 2 can be seen in both ILD and pulmonary arterial hypertension. Currently, I am validating this algorithm in Indian scleroderma patients. I was very interested to see this correlation in the study of Mukerjee et al.
The author has declared no conflicts of interest.
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