An Expert Panel of the Orbital Society reported criteria for the diagnosis of idiopathic orbital inflammation (IOI). The criteria were developed by a Delphi consensus approach amongst expert. Pathologic features are helpful to exclude conditions in the differential diagnosis.

Idiopathic Orbital Inflammation (IOI) may occur as a diffuse myositis (myositic) or as inflammation without diffuse myositis (nonmyositic).


Pathologic features of IOI:

(1) lymphoplasmacytic infiltrate with variable numbers of other inflammatory cells

(2) absence of granulomatous inflammation

(3) absence of vasculitis

(4) absence of necrosis

(5) IgG4-positive plasma cells <= 30 cells per high power field

(6) serum IgG4 to total IgG ratio <=40%

(7) variable fibrosis

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