To distinguish IgG4-related disease from seronegative granulomatosis with polyangiitis

SIR,
IgG4-related disease (IgG4-RD) is a fibro-inflammatory disease that can affect almost every organ. Indeed, previous unexplained conditions have now been reclassified as primarily IgG4-RD and may imitate many inflammatory, infectious and malignant disorders often leading to a delay in diagnosis or incorrect diagnosis. Nasal manifestation of IgG4-RD, mostly of the paranasal sinuses, has previously been described in case reports, but it can also manifest as a primary or secondary nasal disease such as chronic sinusitis and paranasal sinusitis with dacryoadenitis. Since IgG4-RD localized in the nasal or orbital region remarkably resembles limited granulomatosis with polyangiitis (GPA), IgG4-RD could be an alternative diagnosis in ANCA negative limited GPA. After revising the diagnosis to IgG4-RD in patient 1, we re-evaluated two other ANCA negative patients from a funded database with similar clinical features and could alter the diagnosis into IgG4-RD. The histomorphological features matching IgG4-RD and absence of evident features of GPA were the reasons for immunohistochemical analysis in these cases leading to the diagnosis of IgG4-RD. [...]