A 39-year-old Black female patient had, 2 years prior, been diagnosed with SLE according to the Systemic Lupus International Collaborating Clinics (SLICC) criteria, the following of which she fulfilled: antinuclear antibody (ANA), synovitis in 2 or more joints, anti-dsDNA, malar rash, and leucopenia. During outpatient follow-up for SLE, she denied hospitalizations or clinical complications since the last visit. She complained of fatigue on alternating days and non-restorative sleep. She was taking prednisone 20 mg/day, hydroxychloroquine 400 mg/day, and CaCO3 + vitamin D3 (500 mg + 400 IU/day). Upon physical examination, she presented the following: good overall condition, anicteric, afebrile, arterial pressure of 120/80 mmHg, no alterations in the cardiovascular or respiratory system, flaccid and globose abdomen without pain on superficial and deep palpation, well-perfused extremities, and no edemas. There were no alterations on physical exam related to extra-renal lupus disease activity. She brought the routine laboratory exams requested for follow-up for SLE, which are displayed in Table 1. Due to evidence of altered renal function (estimated glomerular filtration rate of 45.8 ml/min/1.73 m2 as calculated by the CKD-EPI equation), subnephrotic proteinuria, and active urinary sediment, which is compatible with proliferative glomerulonephritis, renal biopsy was indicated.
The renal biopsy at light microscopy revealed that 3 of the 13 glomeruli were globally sclerotic, and the remaining were normal. No abnormalities were seen in the vascular compartment. There were no signs of interstitial inflammation. Mild foci of interstitial fibrosis and tubular atrophy were detected; however, a remarkable finding of granular fuchsinophilic hyaline deposits in the tubular basement membrane (TBM) was observed (Figures 1A,B). In relation to immunofluorescence microscopy, the sample contained 6 glomeruli in conditions for analysis, and massive deposits of IgG, C3, C1q, kappa, and lambda were observed in the TBM, in addition to deposits of IgG with mild positivity in the mesangium of the adjacent glomerulus (Figures 1C,D). Immunohistochemical studies revealed predominant deposition of IgG1 and IgG2, but not IgG3 and IgG4 in the TBM (Figures 1E-H). The kidney biopsy showed normal staining for cubilin using a polyclonal antibody along the apical membrane of the tubular epithelium, but tubular basement membrane staining was not detected (Figure 2A). The patient had serum IgG anti-brush border antibody (ABBA) non-reactive to the proximal tubular brush border on sections of normal human kidney (Figure 2B).
In the setting of an autoimmune renal tubulointerstitial disease, a screening for Sjogren's syndrome (SS) was performed, which resulted on positive Anti-SSA and negative Anti-SSB. Despite the presence of SS-A antibodies, diagnosis of SS was ruled out because the patient had no symptoms of dry mouth or eyes, and the biopsy of the minor salivary glands was normal. In post-biopsy outpatient consultation, the patient did not have any new complaints or abnormalities on physical examination. Induction therapy with mycophenolate mofetil (MMF) 3 g/day was initiated and prednisone dose was titrated to 60 mg/day due to the association of histological findings and impaired renal function, with follow-ups scheduled to evaluate clinical/laboratory response and to evaluate corticoid tapering. Induction treatment lasted 6 months, and maintenance treatment was continued with MMF 2 g/day. At 12 months, the patient showed complete remission of proteinuria (Figure 3) and improved renal function (Figure 4). During the period of treatment, the patient did not have flares of the disease, and did not require hospitalization.