Sequential changes in urinary crystal morphology in ethylene glycol poisoning: first human LV-SEM characterization of recovery-phase crystals.

Ethylene glycol (EG) poisoning typically causes severe metabolic acidosis and acute kidney injury (AKI), characterized by urinary calcium oxalate (CaOx) crystals. Although needle-shaped calcium oxalate monohydrate (COM) crystals are a recognized diagnostic marker in the acute phase, sequential changes in urinary crystal morphology during recovery have not been well characterized in human cases. We present a 32-year-old man who developed profound metabolic acidosis (pH 6.747) and AKI (serum creatinine 1.56 mg/dL) after ingesting a lethal dose of EG. Following emergency hemodialysis and fomepizole treatment, urinalysis showed a sequential transition of urinary CaOx crystals from abundant needle-shaped COM in the acute phase to dumbbell-shaped COM and octahedral calcium oxalate dihydrate (COD) by day 14. This transition was observed during recovery, and renal function fully recovered by day 68 (serum creatinine 0.78 mg/dL). Low-vacuum scanning electron microscopy (LV-SEM) provided detailed three-dimensional visualization of these recovery-phase crystals after simple cytospin preparation, without chemical fixation or conductive coating. This report provides the first human LV-SEM visualization and characterization of recovery-phase urinary calcium oxalate crystals in ethylene glycol poisoning. These morphological changes may reflect recovery-related changes in the intratubular environment and offer pathophysiological insight into the transition from the acute toxic phase to recovery.