Sarcoidosis does not belong to or overlap with immunoglobulin G4-related diseases based on an assessment of serum immunoglobulin G4 levels in cardiac and noncardiac sarcoidosis

Although sarcoidosis may exhibit histopathologic features similar to those of a newly emerging clinical entity, immunoglobulin G4-related sclerosing disease, sarcoidosis is currently not considered to be associated with immunoglobulin G4-related immunoinflammation. Not many studies on this association have been reported. We investigated serum immunoglobulin G4 levels among patients with sarcoidosis with or without cardiac involvement (cardiac sarcoidosis and non-cardiac sarcoidosis patients). The mean serum immunoglobulin G4 level among the 65 patients with sarcoidosis was 56.8 ± 43.0 mg/dL, which did not significantly differ between patients with cardiac sarcoidosis (54 ± 48 mg/dL, n = 12) and patients without cardiac sarcoidosis (58 ± 42 mg/dL; n = 53). Serum level of soluble interleukin 2 receptor, a potent marker that may reflect sarcoidosis activity, was elevated in cardiac sarcoidosis (910 ± 683 U/L) and noncardiac sarcoidosis (689 ± 399 U/L) but did not significantly differ between the groups. Immunohistochemistry of cardiac or lymph node specimens from patients with cardiac sarcoidosis showed only sparse or no infiltration of immunoglobulin G4-positive lymphocytes, in contrast to the moderate to severe infiltration of CD68-positive macrophages and CD45-positive lymphocytes. Although the number of study subjects was small, these findings collectively suggest that regardless of the presence or absence of cardiac involvement, sarcoidosis does not belong to or overlap with immunoglobulin G4-related sclerosing disease.