Endoscopically-detected small-intestinal lesions with dense infiltration of IgG4-positive plasma-cells.

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory syndrome characterized by dense IgG4-positive plasma-cell infiltrate and progressive fibrosis. Small intestinal involvement is uncommon, and its clinicopathological spectrum remains unclear. Herein, we describe two older individuals with small intestinal lesions rich in IgG4-positive plasma cells. Case 1 was a 73-year-old woman with known orbital and pancreatic IgG4-RD who developed mild ileal narrowing, detected on surveillance imaging, and elevated serum IgG4 (214 mg/dL). Case 2 was an 87-year-old woman without prior IgG4-RD who presented with bowel obstruction caused by a tight ileal stricture, normal serum IgG4 level (59 mg/dL), and no other organs affected. In both patients, histological examination revealed dense lymphoplasmacytic infiltration, with IgG4/IgG ratios exceeding 40%. Although hyper-IgG4-emia and multiorgan involvement commonly trigger diagnostic suspicion, these cases demonstrate that IgG4-rich inflammation can arise as a solitary manifestation in the small intestine, and may escape detection unless specific immunostaining is conducted. Sequential organ involvement is also possible, underscoring the need for longitudinal follow-up. IgG4‑positive plasma‑cell infiltration should be included in the differential diagnosis of unexplained small‑intestinal ulcers or strictures—even when serum IgG4 is normal and systemic features of IgG4‑RD are absent—as histological confirmation can guide timely immunosuppressive or surgical management.