Topical Sodium Thiosulfate: A Treatment for Calcifications in Hyperphosphatemic Familial Tumoral Calcinosis?

Hyperphosphatemic familial tumoral calcinosis (HFTC) and hyperphosphatemia hyperostosis syndrome (HHS) are rare diseases characterized by hyperphosphatemia and ectopic calcifications or recurrent episodes of diaphysitis. In the setting of metabolic or inflammatory diseases, recent data suggest that systemic administration of sodium thiosulfate (STS) could be effective in the treatment of ectopic calcifications but may also be poorly tolerated (digestive symptoms, metabolic acidosis). Our group developed a topical formulation of STS to treat ectopic calcifications locally, therefore limiting patient exposure to the drug and its adverse effects.We aimed at describing efficacy and tolerance for a topical formulation of STS in treated patients.We performed a retrospective study wherein clinical, radiological, and biological data before and after the application of the topical STS treatment were collected and analyzed.Three patients admitted to 3 different hospitals with an ectopic calcification secondary to HFTC or HHS were treated with topical STS.The topical STS was applied daily by the patients.A significant clinical and radiological decrease of ectopic calcifications was observed after at least 5 months of treatment. The STS treatment was well tolerated and no clinical or biological side effects were observed.Topical STS appears to be a promising treatment for ectopic calcifications secondary to HFTC or HHS.