Peridiaphragmatic inflammation and fibrosis (PDIF) is a radiologic feature in myositis-associated interstitial lung disease (M-ILD). This study aims to formally define PDIF as seen on high-resolution computed tomography (HRCT) and evaluate its association with clinical and serologic features of M-ILD.

We conducted a retrospective review of 46 patients diagnosed with M-ILD at National Jewish Health, who were evaluated for the presence of PDIF on HRCT scans. Three thoracic radiologists developed the criteria, and two independently assessed 169 longitudinal CT scans from the 46 patients for predefined imaging criteria, including PDIF. Demographic, clinical, serologic, and pulmonary function test data were collected and analyzed.

PDIF was identified in 28.2 % (13/46) of patients and in 18.9 % (32/169) of the reviewed scans. Among those with PDIF, 69.2 % had this finding on their initial HRCT scan prior to starting therapy, and it persisted in subsequent scans. PDIF was associated with stable radiologic pattern over time. Patients with PDIF had a high prevalence of anti-Jo antibodies (69 %) and anti-Ro52 antibodies (61.5 %). Despite ongoing treatment, all patients with PDIF experienced dyspnea, and 8/13 had concurrent myositis. There was no significant difference in forced vital capacity (FVC) or diffusing capacity for carbon monoxide (DLCO) trends over time between patients with and without PDIF.

PDIF is a relatively common finding in M-ILD, and appears to be particularly associated with anti-synthetase syndrome. Further research is needed to determine the sensitivity, specificity, and clinical implications of PDIF across all inflammatory ILDs. Early recognition of PDIF may aid in the diagnosis and management of M-ILD, but does not appear to be associated with disease progression.