Significant overlap may occur between idiopathic interstitial pneumonia (IIP) and connective tissue diseases (CTDs) that do not meet the established classification criteria for any known CTDs (i.e., occult CTD). Performing minor salivary gland biopsy (MSGB) to detect occult primary Sjogren's syndrome (pSS) in IIP patients is not well studied.

Consecutive IIP patients underwent MSGB to determine the prevalence of positive MSGB findings. Furthermore, we characterised the clinical, physiological and serological profiles of the MSGB-positive patients. Cox regression models were used to identify independent predictors of survival.

The data of 155 patients with IIP were available for analysis. Sixty patients (38.7%) had positive MSGB findings. Of them, the mean age was 63.3 years, 51.6% were women, usual interstitial pneumonia (UIP) was the predominant pattern (63.3%), and seronegative antibodies (61.6%) were likely. Patients with positive MSGB findings had significantly greater survival than those with negative MSGB findings (p = 0.041). After stratifying the MSGB cohort based on the presence of a UIP pattern, no significant difference in survival was noted between those with positive MSGB-UIP pattern and those with a negative MSGB-UIP pattern (p = 0.231). Multivariate analysis on all UIP patients showed that higher forced vital capacity (p = 0.010) and smoking status (p = 0.035) were independently associated with survival.

A substantial number of IIP patients had underlying occult CTD, highlighting the importance of performing MSGB to identify the salivary component of pSS when evaluating patients with interstitial lung disease of undetermined aetiology.