Another atypical case of acute kidney injury—or not? Answers

In pre-renal acute kidney injury (AKI) without acute tubular necrosis (ATN) we do not expect abnormalities on renal ultrasound, as no structural damage has taken place. The fact that after rehydration urinary output was immediately restored indicates a pre-renal component of the renal dysfunction, but does not explain the ultrasound abnormalities. He was not discharged and additional workup was planned.

Hyperphosphatemia and hyperparathyroidism together typically point more towards chronic kidney disease (CKD) [1, 2] than AKI and this was the initial indication that there might have been a pre-existing renal problem. The ultrasound image is unusual for ATN as in that case we expected a globally increased echogenicity [3]. In addition there is usually a delay in the normalization of urinary output after rehydration [4]. In ATN, urinalysis typically shows epithelial cell casts and free renal tubular epithelial cells [4], which were absent in this case. The ultrasound image thus indicated a different underlying condition than ATN and we decided to perform a renal biopsy to exclude underlying conditions such as glomerulonephritis, tubulointerstitial nephritis, and CKD. Autoimmune antibody testing (antinuclear antibodies, antistreptolysin O antibodies) and complement screening both came back negative.