Bone Abstracts

Background: Hyperphosphatemic familial tumoral calcinosis (HFTC) is characterized by hyperphosphatemia and the formation of tumor-like extra-osseous calcifications. Tumors often necessitate surgical management although medical treatment may limit the need for surgical intervention. We present two cases of HFTC successfully managed with combination acetazolamide (ACTZ) and sevelamer carbonate.

Case Report #1: A 5-year-old African boy with a loss-of-function mutation in the GALNT3 gene presented with bilateral elbow TC and underwent surgical excision at 7 years. At 9 years, he presented with a diaphysitis of the left tibia and recurrence of TC at the left elbow. Combination therapy with ACTZ and sevelamer was initiated. Biochemistry prior to medical therapy was as follows: serum phosphate 2.01 mmol/l (N: 1.2–1.8), 1,25-dihydroxyvitamin D₃ 65 pmol/l (N:39-193), c-terminal FGF23 1435 RU/ml (N:<=230) and serum bicarbonate 27 mmol/l. After 2 years of therapy, his biochemical panel was as follows: serum phosphate 2.34 mmol/l (N:1.05–1.75), 1,25-dihydroxyvitamin D₃ 225 pmol/l (N:48–190) and serum bicarbonate 22 mmol/l. The tumor regressed substantially with little residual signs on plain radiograph and clinically with no limitation of activity. There have been no side effects to the therapy.

Case Report #2: An 11-year-old Arab girl with no mutation in FGF23, KL, GALNT3 and SAMD9 genes presented with TC at the left elbow which was gradually increasing in size over the last 5 years. Combination therapy with ACTZ and sevelamer was initiated at age 12. Biochemistry prior to therapy was as follows: serum phosphate 1.43 mmol/l (N:1.05–1.75) although patient was mildly hyperphoshatemic at presentation (phosphate 1.82 mmol/l), 1,25-dihydroxyvitamin D₃ 143 pmol/l (N:39–193), c-terminal FGF23 60 RU/ml (N:<=230). After 2 years of therapy, the patient remained normophosphatemic with serum phosphate level at 1.27 mmol/l despite maintaining mild metabolic acidosis with serum bicarbonate 18 mmol/l. Clinically, the patient has shown mild regression of the tumor and normal activity. Despite mild hypercalciuria with treatment, there has been no nephrocalcinosis.

Conclusions: Combination ACTZ and sevelamer therapy resulted in significant tumor regression in patient 1, and mild tumor regression in patient 2. The agents were tolerated well without evidence of nephrocalcinosis after 2 years of therapy.

Disclosure: The authors declared no competing interests.