CT sheds light on autoimmune features associated with idiopathic pulmonary fibrosis (IPF) and usual interstitial pneumonia (UIP) -- a boon, as general CT findings sometimes don't follow UPI or probable UPI patterns.
The study results suggest a "different pathophysiologic process behind pulmonary fibrosis," wrote a team led by Sohee Park, MD, of Asan Medical Center in Seoul, South Korea, "which could have distinct implications in diagnosis, prognostication, and management." The group's findings were published March 25 in Radiology.
IPF with autoimmune activity features has been classified as interstitial pneumonia with autoimmune features (IPAF), and these characteristics can "substantially affect the diagnostic process, requiring more comprehensive evaluation to identify underlying CTD [connective tissue disease] and make treatment decisions considering anti-inflammatory approaches," the researchers explained, noting that the clinical, radiologic, and prognostic implications of IPAF in patients with IPF and pathologic UIP have not been fully assessed.
To address the knowledge gap, Park and colleagues investigated whether autoimmune features found on CT imaging could help evaluate the diagnostic and prognostic implications of IPAF in patients with IPF and pathologic UIP. The study included 210 patients with UIP confirmed by lung biopsy between January 2013 and February 2020. The team diagnosed patients with IPAF according to current guidelines; assessed CT patterns that could indicate CTD (anterior upper lobe, straightedge, and exuberant honeycombing signs); and evaluated patients' overall survival.
Of the 210 patients, 23 (11%) had IPAF. The researchers reported the following:
| CT findings in patients with and without usual interstitial pneumonia | ||
|---|---|---|
| Measure | Patients with UIP or probable UIP pattern | Patients with an alternative diagnosis or CT pattern indeterminate for UIP |
| Prevalence of pathologic autoimmune features on CT | 20.3% | 38% |
| Prevalence of serologic autoimmune features on CT | 9.8% | 20% |
They also found that IPAF was not a prognostic factor for overall survival, with a hazard ratio of 0.81 (p = 0.58). But they did report that the presence of lymphoid follicles, CT signs for connective tissue disease, and use of an antifibrotic agent was independently associated with higher overall survival rates (hazard ratio [HR]: 0.59, p = 0.02; HR: 0.31, p = 0.047; and HR: 0.31, p<0.001, respectively) -- and that the presence of higher levels of fibrosis was associated with worse overall survival (HR, 1.08: p < 0.001).
Images in a 57-year-old female with an indeterminate usual interstitial pneumonia (UIP) pattern at CT and pathologic UIP with interstitial pneumonia with autoimmune features (IPAF). (A, B) Axial noncontrast chest CT scans show a multifocal subpleural and patchy peribronchovascular distribution of ground-glass opacities, interspersed with fine reticulation and traction bronchiolectasis (arrows on A and B) that diffusely involves both lungs without a significant basal predominance. Focal areas of layered cysts with traction bronchiectasis and bronchiolectasis are noted in the left upper lobe (arrowheads on A). (C) In the pathologic specimen (original magnification, ×0.5; hematoxylin-eosin stain), the low power view shows patchy, heterogeneous involvement of end-stage fibrosis in subpleural and peripheral distribution with marked pleural and parenchymal cellular infiltration. (D) The high-power view (original magnification, ×0.5; hematoxylin-eosin stain) shows marked lymphoplasmacytic infiltration with lymphoid follicles and lymphoid aggregations (arrows) and multifocal fibroblastic foci (arrowhead). Serologic tests revealed antinuclear antibodies (titer, 1:160) with nucleolar pattern. Therefore, the patient was classified as having IPAF. The fibrosis score was 33.9% at the quantification analysis. The diffusing capacity of the lung for carbon monoxide on initial pulmonary function test was 66%. Despite use of an antifibrotic agent, follow-up CT at 1.2 years showed fibrotic progression of the interstitial lung disease (image not shown). However, the patient was alive 5.3 years after undergoing the initial CT scan. Images and caption courtesy of the RSNA.
In an accompanying editorial, Jeanne Ackman, MD, of Massachusetts General Hospital in Boston, lauded the study for offering further guidance to clinicians tasked with diagnosing idiopathic disease.
"With time, we inevitably will continue to elucidate more etiologies of previously deemed idiopathic diseases, including IPAF and IPF," she noted. "Another incremental step has been made toward this end, which will ultimately guide future beneficial therapies."
The complete study can be found here.
