[Successful steroid therapy for indolent myeloma with kidney injury due to direct infiltration of myeloma cells].

A 68-year-old woman visited JA Toride Medical Center with asymptomatic proteinuria. Bence Jones protein-λ was identified in her serum and urine samples, and subsequent bone marrow aspiration revealed multiple myeloma (MM). Simultaneous renal biopsy showed only minor glomerular abnormality and preserved interstitium. Since the clinical stage was not advanced, aggressive treatment was avoided. During the following six months, her renal function gradually deteriorated with sustained elevation of urine protein and β2 microglobulin excretion, although other routine blood tests yielded stable results. In contrast to the first renal biopsy, the second biopsy specimen exhibited findings suggestive of inflammatory cell infiltration associated with light chain deposition along the tubular basement membrane. However, her myeloma did not cause symptoms other than mild renal disorder and remained in the category of indolent myeloma. Therefore a moderate dose of steroid therapy according to the regimen of common interstitial nephritis was initiated and her renal function and urinary findings partially recovered. Subsequently, her condition was diagnosed as infiltration of plasma cells with positive λ-light chain deposition. Since direct infiltration of myeloma cells into the renal interstitium rarely causes renal failure especially at the initial stage, we did not conduct intensive chemotherapy with possible severe side effects. More intensive chemotherapy would have been administered if the patient had suffered from other organ damage. There are no reports of cases in whom steroid alone was effective against multiple myeloma, hence this case is of clinical significance in providing a treatment option for renal dysfunction caused by restricted infiltration of myeloma cells, especially for cases where intensive chemotherapy is contraindicated.