Tubulointerstitial Nephritis and Uveitis Syndrome: A Report of 6 Cases with Renal Biopsy and Electron Microscopy Evaluation

Tubulointerstitial nephritis with uveitis syndrome is a rare, immune-mediated entity, characterized by oculo-renal inflammation. Diagnosis requires the exclusion of all other causes of tubulointerstitial nephritis (TIN). We present 6 patients with clinical, laboratory, and renal biopsy findings denotative of tubulointerstitial nephritis with uveitis syndrome. All our patients experienced ocular and renal manifestations, defined by bilateral uveitis and photosensitivity, along with a decline of renal function. In some patients, increased serum creatinine was accompanied by non-nephrotic range proteinuria, glucosuria or "full-blown" Fanconi syndrome. The rest of the laboratory evaluation was normal apart from the presence of elevated erythrocyte sedimentation rate and increased urine β2-microglobulin, as well as normochromic, normocytic anemia in some cases. All patients underwent renal biopsy. Histochemical (PAS, Masson, silver, Congo-red) and immunohistochemical stains for immune cell populations (CD3, CD20, CD4, CD8, PGM1, CD138) and for the assessment of β2-microglobulin were conducted. Electron microscopy examination of the biopsies was also performed. Follow-up, ranging from 18 months to 10 years, was available for 4 patients. Histological evaluation revealed interstitial inflammatory infiltration consisting mainly of lymphocytes, with a T-cell predominance, along with several macrophages. Inflammation severity varied among different patients, with some showing scarce foci of immune cell clusters, while others demonstrated a dense, diffuse interstitial infiltration. Interestingly, in 2 cases, a granulomatous pattern, characterized by non-necrotic, ill-defined granulomas was detected. Tubulitis was also encountered in some patients. A divergence was noted regarding the chronicity index, with different levels of tubular atrophy, interstitial fibrosis, and global glomerulosclerosis among different cases. β2-Microglobulin immunohistochemical evaluation revealed a substantial diminishment of cytoplasmic staining in tubular epithelial cells compared to control kidneys. The most notable finding derived from electron microscopy examination was the presence, in 1 patient, of scattered granular electron-dense deposits along some tubular basement membranes. First-line treatment included steroids, supplemented in some cases by additional immunosuppressive agents. Three patients experienced a partial or complete response, while progressive renal damage was observed in a case with severe chronic lesions and persistence of inflammation-triggering factor. Our cases seem to represent progressive stages within the continuum of disease evolution. Patients with more prominent inflammation might represent a more initial state, while those with a more severe chronicity index, probably depict more advanced stages. While the predominance of T-cells predicates a cell-mediated autoimmune mechanism, as the driving force of the disease occurrence, the presence of immune complexes in more advanced stages might indicate the involvement of humoral immunity as a late event during the disease course.