Acute Kidney Injury Secondary to Vitamin D Intoxication: A Case of Oxalate Nephropathy

In recent years, vitamin D supplements have gained popularity in the media, leading more people to start taking them on their own. Vitamin D excess and subsequent intoxication are an uncommon but recognised cause of acute kidney injury. Excess of vitamin D leads to hypercalcaemia with a suppressed parathyroid hormone. Hypercalcaemia leads to hypercalciuria, which in turn causes supersaturation of urine with calcium salts. Deposition of these salts can create a form of acute kidney injury characterised by tubular obstruction and interstitial injury, as seen on a renal biopsy. We report the case of a male in his 70s who presented with confusion and weakness. He was found to have a significant acute kidney injury with a metabolic acidosis. His serum-adjusted calcium was elevated, and he had an elevated phosphate and potassium. His parathyroid hormone level was suppressed, and a myeloma screen was negative. He was initiated on haemodialysis. It was later revealed by a family member that he had been taking large doses of vitamin D daily for more than three years, believing it would boost his immunity during the COVID-19 pandemic. Renal biopsy demonstrated diffuse acute tubular injury with clear refractile crystals within the tubules. The interstitium showed oedema and acute inflammatory infiltrate. He was commenced on prednisolone to suppress further activation of vitamin D and to treat interstitial nephritis. This led to an improvement in his renal function, and dialysis was discontinued. His renal function stabilised, but only a partial recovery was observed. Excessive intake of vitamin D is associated with toxicity and long-lasting consequences. This may be patient-directed or secondary to drug prescription errors. Hypercalcaemia with suppressed parathyroid hormone and hypercalciuria are hallmarks of such toxicity, as seen in our patient. The histopathology in our case showed radially arranged oxalate crystals with associated tubular damage and interstitial inflammation, consistent with crystalline nephropathy. It is important to obtain a detailed history regarding over-the-counter supplement use in these patients, as early recognition allows for timely management, and such information may not be readily volunteered by patients. Prompt intervention and early management may prevent irreversible kidney damage, as evidenced by the partial recovery of renal function observed in our patient.