Periostin: a promising biomarker in nonspecific orbital inflammation and orbit-involving IgG4 disease.

To demonstrate crisp, specific immunohistochemistry (IHC) for periostin and document its utility as a biomarker for nonspecific orbital inflammation (NSOI) and immunoglobulin G4-related orbital disease (IgG4-RD). A multi-institutional retrospective study of both NSOI and IgG4-RD patients. Demographics, clinical disease location, and severity were recorded. Routine histologic sections of affected NSOI and IgG4-RD tissue and fibrocollagenous control tissue were interrogated with an anti-periostin antibody. Ten NSOI patients had orbital manifestations of variable severity involving the lacrimal gland, extraocular muscle, and diffuse or focal orbital tissue. 12 IgG4-RD disease patients had involvement of the lacrimal gland, multifocal orbital disease, or extra-orbital extension. Periostin IHC showed strong, diffuse positivity restricted to pathological fibrotic zones, sparing inflammatory and epithelial elements. This was observed in both the NSOI and IgG4 cases. Periostin is highly expressed in zones of pathologic fibrosis, indicating its potential role in NSOI and IgG4 disease pathogenesis and as a disease biomarker.