Evaluating IgG4-RD Disease Response

We retrospectively reviewed the electronic medical records of these patients at the time of the initial treatment, including age, sex, diagnostic classification, disease duration, affected organs, and treatment regimen. The IgG4-RD responder index (RI), which is a score for each organ system and serum IgG4 level, was calculated to assess the disease activity [8 (link)]. Laboratory parameters such as erythrocyte sedimentation rate (reference value: 0–20 mm/hr) and the levels of C-reactive protein (reference value: 0–0.6 mg/dL), serum IgG (reference value: 700–1,600 mg/dL), and serum IgG4 (reference value: 6–121 mg/dL) were also collected. Serum IgG levels were measured using nephelometry (Nephelometer, Dade Behring, Germany) and serum IgG4 levels were measured using a single radial immunodiffusion method (The Binding Site, Birmingham, UK).
At six months of initial treatment, the clinical and serological response was assessed. The clinical response included the IgG4-RD RI score, > 50% decline in IgG4-RD RI score, and remission. Remission was defined as meeting all of the following [16 (link)]: (1) > 50% decline in IgG4-RD RI score; (2) tapering of prednisolone to less than 10 mg/day; and (3) no relapse during the initial treatment period (within six months). Relapse was defined as recurrence, worsening, or de novo organ involvement as determined via imaging or the analysis of biochemical parameters (e.g., urinalysis and liver function), regardless of serum IgG4 levels. The change of serum IgG4 levels at six months was also evaluated as the serological response. Patients were divided into two groups according to serum IgG4 levels at six months (normalized and elevated serum IgG4 levels).