# Primary hyperoxaluria type I diagnosed after a kidney transplant presenting with subcutaneous calcification: a case report of sodium thiosulfate treatment

## TL;DR

A rare kidney disease was diagnosed after a transplant, and treatment with sodium thiosulfate helped reduce harmful calcium deposits in the skin.

## Contribution

This case report presents a novel use of sodium thiosulfate in treating subcutaneous calcification in PH1 patients post-transplant.

## Key findings

- The patient had a frameshift variant in the AGXT gene, confirming PH1 diagnosis.
- Sodium thiosulfate treatment led to the disappearance of subcutaneous calcification in the left-hand ring-finger.
- Skin biopsy showed calcium oxalate crystals without vascular oxalosis.

## Abstract

Primary hyperoxaluria (PH) is a rare autosomal recessive disorder that results from the overproduction of endogenous oxalate. The diagnosis of PH is often delayed or missed owing to its rarity, variable clinical expression and other diagnostic challenges. In this study, we report a patient with a frameshift variant, c.823_824dup, in the alanine-glyoxylate aminotransferase (AGXT) gene of PH1 who presented with renal failure recurrence after kidney transplantation, arteriovenous fistula (AVF) occlusion and subcutaneous calcification in adulthood. Skin biopsy revealed heavy deposition of calcium oxalate crystals in subcutaneous tissue without vascular oxalosis. After 6 courses of sodium thiosulfate (STS) treatment, X-rays of the bilateral hands showed the disappearance of subcutaneous calcification on the extremity of the left-hand ring-finger. This case highlights the importance of broad diagnostic testing prior to transplantation in patients who present with end-stage renal disease with unclear etiology. In addition, STS may be useful for PH1 patients with subcutaneous calcium deposits.