Unusual Presentation of Sjogren Disease with Proximal Renal Tubular Acidosis

Introduction: Sjogren’s disease (SD) has many renal manifestations. We present a case of type 2 (proximal) renal tubular acidosis (pRTA) with Fanconi syndrome and tubulointerstitial nephritis (TN) treated with maintenance mycophenolate mofetil (MMF), tacrolimus (TAC) and low dose steroids in a SD patient. Case Description: 69-year-old female with history of SD presented for evaluation of elevated creatinine (Cr). The patient’s SD symptoms were bone pain, stiffness in her lower extremities eventually leading to a wheelchair bound state and dry mucous membranes. She denied any family history of kidney disease. Labs showed a Cr 1.36 mg/dl, bicarbonate 18 mmol/L, potassium 3.2 mmol/L, glucose 96 mg/dl, phosphate 1.7 mg/dl, uric acid 1.6 mg/dl, vitamin D 25 OH 19 ng/ml, vitamin D 1, 25 OH 15 pg/ml. Urinalysis was significant for pH 6, sterile pyuria and glucosuria. Her fractional excretion of phosphate was 34.6%. Lab work was consistent for pRTA. Due to the sterile pyuria, a renal biopsy was done which showed acute on chronic TIN with severe activity. The patient started 50 mg of prednisone daily. Metabolic derangements were treated orally. Unfortunately, her TIN quickly relapsed when steroids were tapered prompting initiation of MMF with another steroid taper. She again relapsed when steroids were weaned. At this point, a multitargeted immunosuppression regimen was initiated with prednisone 10 mg/day, MMF 1000 mg twice daily, and TAC with a trough goal 4-7. On this regimen, the patient’s Cr has remained stable at 1.2 mg/dl with no additional flares for the last 9 years. Her prednisone was also tapered down to 5 mg. Clinically, the patient’s bone pain and wheelchair bound state improved after treatment with active vitamin D and oral phosphate. Discussion: TIN is the most common kidney manifestation in SD. Most patients are treated with 1 mg/kg of prednisone with a taper. Maintenance therapy usually involves MMF or azathioprine. TAC is rarely used for TIN in SD. In this patient’s biopsy, the TIN appeared similar to acute cellular rejection and thus was treated with transplant immunosuppressive medications. PRTA occurs in around 3% of patients with SD. PRTA can lead to Fanconi's syndrome resulting in a normal anion gap metabolic acidosis, phosphaturia, glycosuria and aminoaciduria. Treatment usually involves supplementation of bicarbonate and electrolytes such as potassium and phosphate.