Diagnosis requires tissue biopsy of an affected organ with characteristic histological findings. Serum immunoglobulin G4 is often elevated but this is not always the case.
IgG4-related disease
IgG4-related skin disease
Anti-IgLON5 disease
IgA vasculitis
Isolated primary immunoglobulin M deficiency
Antisynthetase syndrome
Undifferentiated connective tissue disease
Leukotriene receptor antagonist-associated Churg–Strauss syndrome