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

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.

Keywords: AGXT gene; primary hyperoxaluria; skin biopsy; sodium thiosulfate; subcutaneous calcification.

FIGURE 1

Clinical and imaging presentations of the patient. (A) The presence of subcutaneous nodule on left hand ring-finger. (B) X-rays of bilateral hands showed subcutaneous calcification on the extremity of left-hand ring-finger (red arrow). (C) Subcutaneous nodule on left hand ring-finger disappeared after STS treatment. (D) X-rays of bilateral hands showed the disappearance of subcutaneous calcification on the extremity of left-hand ring-finger after STS treatment (yellow arrow).

FIGURE 2

Computed tomography of the abdomen and pelvis showed nephrocalcinosis in (A) both kidneys (yellow arrow) and (B) transplanted kidney (red arrow).

FIGURE 3

Examination of the calcium oxalate crystals on skin biopsy and AVF sample. (A) HE staining showed the deposition of crystal substance in skin biopsy sample. (B) Von Kossa staining showed black calcified deposits in skin biopsy sample. (C) The representative picture of birefringence on polarized microscopy in skin biopsy sample. The calcified crystals polarize and thus are calcium oxalate. (D,E) The representative image of HE (D) and Von kossa staining (E) in subcutaneous artery from skin biopsy sample. (F,G) The representative image of HE staining (F) and birefringence on polarized microscopy in AVF samples (F,G).

FIGURE 4

The Whole Exome Sequencing (WES) of the patient and family members and structural evaluation of AGXT variant. (A) WES revealed AGXT c.823_824dup (p. Ser275ArgfsTer38) variant in patient (red arrow). (B) Visualization of the wild and c.823_824dup variant of AGXT gene using swiss-model. (C) The pedigrees of the family with digenic inheritance.