Routine IgG4 staining in minor salivary gland biopsy in a cohort of Italian Caucasian patients suffering from xerostomia

IgG4-related disease is a potentially systemic disease mimicking and overlapping with different autoimmune diseases, such as primary Sjögren's syndrome (pSS). The involvement of salivary glands, previously called Mikulicz's disease, has been reclassified as IgG4-related sialadenitis (SA). The aim of this study was to assess the prevalence of IgG4-SA in a cohort of Italian Caucasian patients presenting with xerostomia and to evaluate the eventual overlap between IgG4-SA and pSS. We included 154 patients - 15 males and 139 females, mean age 54.18 ±14.24 years, who underwent minor salivary gland biopsy between March and December 2019 for xerostomia. Histopathology was evaluated using Chisholm-Mason (CM) and focus score (FS) for pSS and immunohistochemical study with IgG4 staining for IgG4-SA were performed. Serum autoantibodies (anti-SSa/RoAb, anti-SSB/LaAb, antinuclear antibodies, rheumatoid factor) were also assessed. In 69 patients (44.8%) FS 0 was found, while FS ≥ 1 was presented in 85 (55.2%). Chisholm-Mason score < 3 and CM ≥ 3 was found in 73 (47.4%) and 81 (52.6%) cases, respectively. IgG4/high-power field level was 20 in 3 pSS patients (1.9%), but none of them had an IgG4/IgG ratio ≥ 40, as well as tissue fibrosis with storiform pattern, obliterative vasculitis, and tissue eosinophilia. The diagnosis of pSS, was confirmed in 92 patients (59.74%). No patient was definitively diagnosed with an IgG4-related disease. In the case of xerostomia, the evaluation of the histopathological specimen for IgG4 should not be routinely performed, at least in an Italian-based Caucasian population. Moreover, immunohistochemistry should not be requested in the case of a negative result of biopsy for pSS.