A 72-year-old man was referred to a nephrology clinic because of an increase in creatinine from 1.2 to 2.2 mg/dL. He has a complicated medical history of neurogenic bladder, benign prostatic hyperplasia (BPH), HIV, and metastatic squamous cell carcinoma of the left mandible post resection. He underwent cisplatin-based chemotherapy and radiation 3 years previously. For the past 2 years, he has been on pembrolizumab. HIV is well controlled with a combination of rilpivirine, emtricitabine, and tenofovir. He is incontinent and wears a diaper. He is being followed up closely for neurogenic bladder, and the most recent imaging did not reveal significant post-void residual (PVR).

Upon further inquiry during the history taking, the patient reports that he has been taking Advil PM as a sleep aid for the last few months. He was instructed to stop all NSAIDs, and his HIV regimen was changed to a nontenofovir-containing formula after discussion with his HIV physician. Pembrolizumab was held temporarily due to increased creatinine. His creatinine gradually improved to 1.6 mg/dL within the next 2 months. Pembrolizumab was restarted. Serum creatinine was checked monthly and remained at 1.6 to 1.8 mg/dL for the following 5 months. However, in month 6 after resumption of pembrolizumab, serum creatinine increased to 5.1 mg/dL. The patient has been in his usual state of health, and oral intake was unchanged. He denied any new symptoms such as dyspnea, swelling, diarrhea, decreased urine output, rash, joint pain, or fever. He has not had any new medications recently and did not restart NSAIDs.

Urine sediment in the clinic is bland. Other relevant laboratory test results are listed below:

  • Urinalysis: 30 mg/g protein, negative for blood, otherwise unremarkable.
  • Urine protein-to-creatinine ratio: 0.5 g/g
  • Urine albumin-to-creatinine ratio: 220 mg/g
  • Serum and urine protein electrophoresis did not reveal any paraproteins or monoclonal spike.
  • Hemoglobin 11 g/dL
  • Platelet count 186 x 103/µL
  • All serologies are negative including anti-nuclear antibody (ANA), anti-double stranded DNA antibody negative (anti-dsDNA), anti-neutrophil cytoplasmic antibody negative (ANCA), complement C3 and C4 levels are within normal range.
  • HIV viral load is undetectable.
  • Serum electrolytes are within normal limits.

A renal biopsy showed prominent interstitial inflammation composed of lymphocytes, histiocytes, and eosinophils (Figure 1). There is 30% global glomerular sclerosis, 50% interstitial fibrosis and tubular atrophy, but no evidence of immune complex-mediated glomerulonephritis.

Figure 1. H&E staining of the patient’s kidney biopsy sample showing prominent interstitial inflammation with many lymphocytes and eosinophils.
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