Immunoglobulin G4-related disease with scant tissue IgG4.

A 56-year-old man was admitted to our hospital for renal dysfunction and symmetrical swelling of submandibular glands. Laboratory and imaging findings were consistent with immunoglobulin G4-related disease (IgG4RD). Histological findings of the submandibular gland and the kidney were also consistent with IgG4RD. However, the patient did not have elevated serum or tissue IgG4 levels. Oral prednisolone therapy, initially 50 mg/day and gradually tapered over 12 months, improved his laboratory abnormalities and the swelling of his affected organs. These findings prompted our final diagnosis of IgG4RD. IgG4RD is a newly recognised disease with an unknown aetiology. This case suggests that IgG4 antibodies do not play a primary role in the aetiology of IgG4RD. Furthermore, clinicians should not exclude the diagnosis of IgG4RD in patients lacking elevated IgG4 levels in their affected tissues, particularly if they have other features of IgG4RD. Steroid therapy should be considered for such patients.