Solving an unusual case of acute kidney injury: Answers

Acute tubular necrosis due to ingestion of an unknown nephrotoxic agent.

A kidney biopsy is necessary to confirm the diagnosis of suspected acute kidney injury (AKI) due to ingestion of a nephrotoxic agent. The kidney biopsy demonstrated significant acute tubular injury with features of acute tubular necrosis on light microscopy (Figure 1) including irregular tubules with luminal dilation, necrosis, and detachment of tubular epithelial cells from the basement membrane with pyknotic nuclei and cytoplasmic vacuolation. The glomeruli, interstitium, and direct immunofluorescence was unremarkable.

Comprehensive drug screen can be helpful in identifying toxic agent(s). After further discussion of the biopsy results with the patient in private, he admitted to taking ~25–30 over-the-counter cough and cold medications to “get high” approximately 24 h prior to his presentation. Original urine and blood samples collected at our facility were then retrieved for additional analyses. An expanded urine drug screen for > 200 drugs was performed by gas chromatography–mass spectrometry (GC-MS) (Agilent Technologies, Santa Clara, CA). A large peak matching with dextromethorphan and a small peak matching with guaifenesin were detected and consistent with the patient’s reported ingestion. The blood sample with adequate volume collected 9 h after arrival to our hospital was sent to NMS laboratories (Willow Grove, PA) for dextromethorphan and guaifenesin quantification by liquid chromatography–tandem mass spectrometry. Concentrations of guaifenesin (therapeutic range, 0.3–1.4 mcg/mL) and dextromethorphan (therapeutic range, 10–40 ng/mL) were 0.13 mcg/mL and 290 ng/mL, respectively. Despite the significant time lapse between ingestion and specimen collection (estimated ~36 h), the dextromethorphan concentration was still well within the toxic range (toxic > 100 ng/mL).

Due to worsening AKI with a rapid progression of BUN from 36 to 83 mg/dL and serum creatinine from 3.27 to 9.43 mg/dL in 36 h, a tunneled hemodialysis catheter was placed. The patient received a total of three sessions of hemodialysis. He required amlodipine and clonidine for hypertension. After 4 days of complete anuria, he began to experience kidney recovery. Laboratory testing on discharge 1 week from admission showed normal serum electrolytes with serum creatinine 1.21 mg/dL (Figure 2). He was discharged after receiving counseling for his drug ingestion with continued outpatient follow-up arranged for ongoing management of AKI and solitary kidney. Follow-up 3 weeks later demonstrated normal serum creatinine of 0.87 mg/dL and an unremarkable urinalysis, with normal urine protein/creatinine ratio of 0.09 mg/mgCr, and blood pressures well-controlled on amlodipine.