Hypercalcemia in IgG4-Related Tubulointerstitial Nephritis: An Unusual Presentation

Introduction: Tubulointerstitial nephritis IgG4 type (TIN-IgG4) is a rare autoimmune kidney condition characterized by IgG4-positive plasma cell infiltrates, leading to renal interstitium inflammation and fibrosis. Associated with IgG4-related disease affecting various organs, diagnosis involves elevated IgG4 levels, with hypercalcemia hinting at parathyroid involvement. This case presents TIN-IgG4 with hypercalcemia without parathyroid abnormalities, detailing clinical presentation, diagnostic workup, and treatment strategies. Case Description: A 30-year-old female (a known case of cholelithiasis and hypothyroidism) presented with malaise, vomiting, abdomen pain and dizziness for 3-5 days. Investigations showed hypercalcemia, 24-hour urinary calcium of 288 mg/dL, creatinine of 770 mg/day and protein of 301 mg/dL (Table). Ultrasound showed signs of medullary nephrocalcinosis. There was no evidence of parathyroid adenoma. Renal biopsy confirmed the diagnosis of TIN-IgG4 based on histopathological findings of interstitial fibrosis, tubular atrophy, and abundant IgG4-positive plasma cell infiltration. Serological testing for free light chains (Kappa and Lambda), renal ultrasound and CT, and histopathological examination of renal tissue were obtained. Serum IgG4 level was elevated and imaging findings supported TIN-IgG4 diagnosis. Denosumab, steroids along with her routine thyroid medications were initiated. Long-term management involves regular monitoring of renal function, disease activity, and avoiding potential complications such as renal failure or systemic involvement. Discussion: Early recognition and intervention in TIN-IgG4, including thorough evaluations for hypercalcemia, are crucial for favorable outcomes and preventing disease progression. Laboratory values on admission - Laboratory Tests Values Urine report/24 hrs Values Serum urea 72 mg/dL Calcium 288 mg Serum creatinine 3.04 mg/dL Creatinine 770 mg PTH 7 pg/mL Protein 301 mg Kappa free light chain 56.70 mg/L - - Lambda free light chain 29.20 mg/L - - 1,25 dihydroxyvitamin D3 13.7 pg/mL - - Total IgG 15.90 g/L - - IgG, immunoglobulin G; P-ANCA, perinuclear antineutrophil cytoplasmic antibodies; PHT, parathyroid hormone.