Researchers have identified clinical features that could help predict which patients with systemic sclerosis (SSc) are likely to go on to develop pulmonary arterial hypertension (PAH) and therefore benefit most from early treatment.
They found that SSc-related PAH was more likely to develop in patients who had a low diffusion capacity for carbon monoxide (DLco; <55% predicted) and therefore a high ratio of forced vital capacity (FVC) to DLco (>1.6), an echocardiogram systolic pulmonary arterial pressure (sPAP) above 40 mmHg and exercise-induced hypoxia.
DLco below 55% predicted was the most sensitive risk factor (82%), while exercise-induced hypoxia was the most specific (73%). The latter was also the most significant risk factor, with affected patients five times more likely to develop SSc–PH than unaffected patients.
The 251 study participants were enrolled in the Pulmonary Hypertension Assessment and Recognition of Outcomes in Scleroderma (PHAROS) study. The average duration of SSc was 9.9 years and the patients were considered to be at risk of PAH due to having one of three criteria: increased sPAP, a low DLco or a high ratio of FVC to DLco.
Over a mean follow-up of 2.5 years, 82 patients underwent right heart catheterization because of suspected PAH and the condition was confirmed in 35.
Most (76%) of these 35 patients met the pre-defined criteria for pulmonary function testing, and had a mean DLco of 46.4% predicted, compared with 51.3% for the remaining at-risk patients who did not develop PAH. This resulted in an average ratio of FVC to DLco of 2.0% versus 1.8%.
Patients who developed PAH also had significantly higher baseline sPAP than the other patients, at an average of 43.2 mmHg versus 38.5 mmHg.
But the researchers, led by Vivien Hsu (Rutgers-RWJ Medical School, New Brunswick, New Jersey, USA), note that less than half of the new PAH group met the echo entry criteria, so sPAP “lacked sufficient sensitivity and specificity to be used as the only screening tool.” Right heart catheterization was necessary to confirm or exclude PAH.
Aside from the predefined criteria, patients who developed PAH were significantly more likely to have exercise-induced hypoxia at baseline, at a rate of 53.9% versus 23.5%. They also had a shorter average 6-minute walk test, at 353 versus 422 metres.
“This ongoing prospective study is an important resource to elucidate outcomes and risk factors for PAH”, the researchers conclude in Seminars in Arthritis and Rheumatism.
“We remain optimistic that early identification and treatment of SSc–PH will significantly alter the long-term outcome of these patients.”
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