A CT-based risk prediction tool developed specifically for patients with RA-associated interstitial lung disease (RA-ILD) has been shown to be more accurate than tools developed for patients with idiopathic pulmonary fibrosis (IPF).

The new model is based on four significant risk factors for ILD survival of age (> 60) and imaging parameters of fibrosis score > 20%, a UIP pattern and emphysema.

It was developed by clinicians in South Korea based on a derivation cohort of 153 patients with ILD, in whom they found that the four parameters were significant predictors of mortality after a median follow up of 54 months.

They designed a tool based on assigning points to each of the parameters and stratifying patients into Stages I (0 points), II (1-3 points) and III (4-5 points) for prognosis.

When tested in a validation cohort of 149 patients with RA-ILD, the tool performed better than the existing GAP prediction model that was developed for patients with IPF. When used to predict five year mortality, the RA-ILD risk prediction model had a C-index of 0.780 compared to 0.623 with the GAP model.

The RA-ILD risk model divided patients into three groups with one-year mortality rates of 0%, 5.1% and 24.1%, respectively.

Writing in Respirology, the study authors said their CT-based risk prediction model gave a better guide to prognosis for patients with RA-ILD than models based on physiological parameters. They conceded that use of the fibrosis score cut-off may be difficult in patients with marginal scores in the range of 10-30%, but said that an FVC threshold of 70% predicted or less could be substituted instead of this parameter with equally accurate results.

“Our study is the first to develop a risk prediction model specifically for the mortality of patients with RA-ILD [and] our results suggest that a CT-based risk prediction model may be useful for predicting the prognosis of patients with RA-ILD,” they said.

In a linked commentary, Dr Matthew Parker of the Department of Rheumatology, Royal Prince Alfred Hospital, Sydney, and Dr Tamera Corte of the Centre of Research Excellence in Pulmonary Fibrosis, NSW, said it was pleasing to see that risk stratification for RA-ILD patients could be possible with only age and high-resolution CT (HRCT) data.

The RA-ILD model would have potential advantages in circumstances where pulmonary function tests are not available, they said.

“It is pleasingly straightforward in its inclusion of only age and radiological parameters. We look forward to further refinement of this or further scoring systems to evaluate disease progression in addition to mortality,” they concluded.