Pleuritis, pulmonary hypertension and shrinking lung syndrome have all been associated with systemic lupus erythematosus but a new study of lupus-associated ILD highlights some of the academic and clinical challenges of rare complications.
A French study has found that while indeed rare, ILD in lupus was a major independent risk factor for death.
The study of 37,393 lupus patients with at least one hospital stay during the study period found 1.2% had an ILD diagnosed at baseline in 2011-2012.
Of the remaining patients, 2.6% were diagnosed with an ILD between 2013 and 2020.
The study, published in Respirology, said the incidence rate of ILD in SLE overall was 10.26 for 1000 patient-years (95% CI 10.24–10.28).
It found ILD was significantly associated with an increased risk of death in SLE patients (HR [95% CI] 1.992 [1.420–2.794]; p < 0.0001).
“Although ILD was considered to have a limited impact on global outcome in previous reports, it is independently associated with a premature death in our study, with an HR similar to chronic kidney disease in SLE.”
The study found risk factors for ILD in lupus were older age (55 [44–64] vs. 44 [33–58] years; p < 0.0001) and male gender (20.9% vs. 13.4%; p = 0.012).
“Interestingly, the frequency of ILD in SLE was higher in patients who had another autoimmune disease – such as Sjögren’s syndrome or systemic sclerosis – associated with SLE (29.9% vs. 5.9%; p < 0.0001),” it said.
The study was unable to determine if any ILD pattern such as non-specific interstitial pneumonia, usual interstitial pneumonia, organising pneumonia, diffuse alveolar damage and/or lymphocytic interstitial pneumonia was specifically associated with SLE.
Commenting on the study in an editorial, Dr Greg Keir said the study highlighted the challenge of rare diseases generally, “and ILD in particular”.
He said the incidence of ILD was heavily dependent on the diagnostic test performed.
“Given the nationwide, retrospective study design, and lack of an accepted definition of precisely what constitutes SLE-ILD, variation in how ILD is defined is not unexpected.”
“While HRCT is often the initial diagnostic test for suspected ILD, this has not been explicitly stated in the study, and presumably a level of granular detail beyond the scope of the PMSI [nationwide medical information] database to capture.”
Dr Keir, from the Princess Alexandra Hospital in Brisbane, agreed the finding of higher rates of ILD in SLE patients with co-existing autoimmune disease was interesting.
“All these conditions (with the possible exception of Sjögren’s syndrome) have a higher prevalence of ILD compared to SLE, and while attributing causality is difficult, it is possible that at least some cases of ILD are more likely related to co-morbid autoimmune disease rather than SLE.”
He said the study also highlighted the comparatively slow progress in effective treatment and better outcomes for CTD-ILD, at least as compared to IPF.
“The development of large-scale ILD registries with well-characterised patient populations, and a growing appreciation of the overlapping inflammatory and pro-fibrotic mechanisms driving CTD-ILD progression are likely to play key roles in future research.”