Clinical features, radiological findings and prognosis of microscopic polyangiitis with interstitial lung disease: a retrospective matched control study

Background: The association between interstitial lung disease (ILD) and microscopic polyangiitis (MPA) has received increasing attention in recent years. However, there are still no studies comparing clinical characteristics and prognoses between MPA-ILD patients and patients with ANCA-negative ILDs. Therefore, the purpose of this study was to analyse a group of patients presenting MPA-ILD matched with patients exhibiting ANCA-negative ILDs to identify differences in their clinical characteristics and survival. Methods: This study retrospectively reviewed the data of 60 patients with MPA-ILD and 60 patients with ANCA-negative ILDs who were matched for age, sex, and patterns on chest high-resolution CT (HRCT) images. The baseline clinical information, laboratory parameters and chest CT data were collected and analysed at each patient's initial diagnosis. Results: Sixty of the 682 (8.8%) ILD patients were diagnosed with MPA-ILD. MPA-ILD patients tended to be older and have higher CRP and ESR levels. ILD antedated MPA in 61.7% (37/60) of the patients, and MPA occurred on average (45.1 +/- 33.4) months after the ILD diagnosis. Compared with matched ANCA-negative ILD patients, MPA-ILD patients had higher CRP and serum creatinine levels and lower haemoglobin levels. UIP (63.3%) was the most common chest HRCT pattern, and the proportion of patients with oddly shaped cysts (P = 0.04) was significantly greater in the MPA-ILD group than in the matched ANCA-negative ILD group. The number of MPA-ILD patients was significantly shorter than that of ANCA-negative ILD patients (P = 0.005). Survival analysis revealed that acute exacerbation (AE) of ILD (HR 2.40, 95% CI 1.03-5.59, P = 0.043) and diffuse alveolar haemorrhage (HR 3.42, 95% CI 1.09-10.73, P = 0.036) were independently associated with shorter survival and that receiving glucocorticoids combined with immunosuppressants (HR 0.11, 95% CI 0.03-0.37, P < 0.001) was independently associated with prolonged survival in MPA-ILD patients. Conclusions: The proportion of MPA-ILD patients with total ILD is not low, and ANCA testing of ILD patients is necessary. Oddly shaped cysts with a UIP pattern may be a characteristic chest imaging manifestation of MPA-ILD. The prognosis of MPA-ILD is poor, especially for patients who are older, have DAH, and have experienced AEs.