BACKGROUND Although most cases of tubulointerstitial nephritis in paraproteinemia are monoclonal light chain deposition-mediated, interstitial nephritis as neoplastic interstitial cell infiltration has rarely been described. On the other hand, lympho-plasma-cell-rich tubulointerstitial nephritis, in which the infiltrative cells are usually polytypic, is often evident in primary Sjögren's syndrome (pSS). Herein we present a rare case of pSS in a patient who had been diagnosed as having IgA kappa-type monoclonal gammopathy of undetermined significance (MGUS) and developed tubulointerstitial nephritis with monotypic (IgA kappa) lympho-plasmacytic infiltrates. CASE PRESENTATION A 74-year-old Japanese woman with pSS who had been diagnosed as having IgA kappa-type MGUS developed progressive renal dysfunction. Renal biopsy revealed tubulointerstitial nephritis with abundant plasma cell-rich mononuclear cell infiltrates without atypia. Immunohistochemical staining for immunoglobulins and light chains showed that most infiltrates were positive for IgA and kappa. Most of the infiltrative cells were positive for CD38 and CD138, and cells positive for CD 19 and CD 45 were also widely evident. Electron microscopy and immunofluorescence studies revealed no apparent immunological deposits in the glomeruli and tubules. Bone marrow and whole-body radiological examinations revealed no findings suggestive of multiple myeloma or lymphoma. Renal function improved rapidly with prednisolone 40 mg daily and has been maintained at the same level on low-dose prednisolone and azathioprine for 18 months. CONCLUSION Tubulointerstitial nephritis with monotypic cell infiltrates, without immunological deposits, is a quite rare histological picture in MGUS, and might be a unique renal manifestation in patients with pSS.

中文翻译：

---

患有原发性干燥综合征（Sjögren's syndrome）并伴有IgA型单克隆性丙种球蛋白病的患者，伴有单型淋巴胞浆浸润的肾小管间质性肾炎。

背景技术尽管副蛋白血症中的大多数肾小管间质性肾炎病例是由单克隆轻链沉积介导的，但由于肿瘤性间质细胞浸润，间质性肾炎很少被描述。另一方面，在原发性干燥综合征（pSS）中，通常存在浸润细胞通常是多型性的，富含淋巴-浆细胞的肾小管间质性肾炎。在此，我们介绍了一例罕见的pSS患者，该患者已被诊断为具有不确定性的IgA kappa型单克隆球蛋白病（MGUS），并发展为具有单型（IgA kappa）淋巴-浆液性浸润的肾小管间质性肾炎。病例介绍一名74岁的日本pSS妇女，被诊断患有IgAκ型MGUS，发展为进行性肾功能不全。肾活检显示肾小管间质性肾炎伴大量浆细胞丰富的单核细胞浸润，无异型性。免疫球蛋白和轻链的免疫组织化学染色显示，大多数浸润液对IgA和kappa呈阳性。大多数浸润细胞对CD38和CD138呈阳性，而对CD 19和CD 45呈阳性的细胞也广泛存在。电子显微镜和免疫荧光研究表明，在肾小球和肾小管中没有明显的免疫沉积物。骨髓和全身放射学检查未发现提示多发性骨髓瘤或淋巴瘤的发现。每天泼尼松龙40 mg可使肾功能迅速改善，并且在低剂量泼尼松龙和硫唑嘌呤上维持相同水平达18个月。