Maintenance of clinical remission with cyclosporine after discontinuation of prednisolone in a patient with tubulointerstitial nephritis with IgM-positive plasma cells

Tubulointerstitial nephritis (TIN) with IgM-positive plasma cells (IgMPC-TIN) is an inflammatory disease characterized by the infiltration of IgM and CD138 dual-positive plasma cells into the renal interstitium. Steroid treatment is effective for many cases of IgMPC-TIN. However, the optimal dose and duration of steroid therapy remain poorly understood. In the present case, IgMPC-TIN was diagnosed in a 36-year-old woman with femoral head osteonecrosis. After administration of prednisolone (PSL, 20 mg/day), several markers of disease activity gradually decreased. The PSL dose was tapered to 5 mg/day for one year without TIN recurrence. To avoid exacerbation of bone lesions due to prolonged administration of PSL, cyclosporine was added to PSL. Combination treatment with 5 mg/day PSL and 100-125 mg/day cyclosporine stabilized the TIN. The patient remained stable without recurrence after further reduction and discontinuation of PSL. This case provides original evidence regarding the optimal treatment regimen for patients with IgMPC-TIN who are unsuitable for prolonged PSL administration.