Bone Abstracts

Introduction: Hyperphosphatemic familial tumoral calcinosis is a rare genetic disorder causing reduced FGF23 activity. Recurrent and occasionally disabling subcutaneous calcifications are major disease manifestations. We describe the successful use of acetazolamide in two cases presenting in childhood with a homozygous GALNT3 mutation.

Case 1: A five year old girl developed tender subcutaneous calcifications in the right elbow which were surgically resected. A year later, she presented with painful new calcifications around the left elbow associated with acute inflammation.

Case 2: A 2.5 year old girl presented with subcutaneous calcifications in her right elbow which were surgically resected on two occasions, with recurrence of tender lesions at 5 years of age at the same site, this time with an additional new large, inflamed lesion in the left hip. Both cases were of African origin with unaffected family members.

Biochemistry: Typical biochemistry with elevated serum phosphate 2.1–2.4 mmol/L (0.9–1.8 mmol/L) but normal calcium, alkaline phosphatase and parathyroid hormone levels noted in both cases.

Management: Acetazolamide was commenced at 20 mg/kg per day in two divided doses. Treatment was monitored with weekly blood gas analysis, aiming for a bicarbonate levels of 16–19 mmol/L. Acetazolamide was reduced to 15 mg/kg/day in Case 1 and increased to 35 mg/kg/day in case two over eight to ten weeks. Case 1 was managed with acetazolamide monotherapy. Case 2 was initially started on sevelamir which was continued, with addition of acetazolamide and topical 25% metabisulfite.

Treatment response: Substantial resolution of pain and swelling was noted both clinically and radiologically by 12 weeks of commencing oral acetazolamide. No significant adverse effects were reported. Clinical effects were sustained at one year in Case 1 and two years in Case 2 at last follow up.

Conclusion: Oral Acetazolamide is a well-tolerated and effective treatment option in children with subcutaneous calcifications in hyperphosphatemic tumoral calcinosis.

Disclosure: The authors declared no competing interests.