Ectopic soft tissue calcifications or ossifications can complicate the course of numerous diseases; most of them are rare or very rare. Even if the clinical, radiological and pathological presentation of ectopic calcifications and ossifications are different, the same hypotheses are discussed considering their hypothetical pathophysiology. Indeed, high calcium phosphate product, local cellular lesions and abnormal transdifferentiation of mesenchymal cells are regularly evoked when pathophysiology of such calcifications or ossifications are discussed. Apart from several case reports that have not been confirmed so far, no medical treatments are available, leading to significant pain and impairment of quality of life for patients. Therefore, only surgical treatment can be proposed when the volume or the consequences of these calcifications/ossifications become too important.

Sodium thiosulfate (STS) is currently used as a cyanide poisoning antagonist and a chemoprotectant against adverse effects of several chemotherapies such as Cisplatin. Numerous case reports and several studies have revealed the potential interest of STS in the treatment of uremic induced vascular or soft tissues calcifications. Recently, our group has developed an expertise in the use of STS for the treatment of ectopic soft tissue calcifications or ossifications. Considering these promising preliminary data, and their limits, we developed a strategy to treat soft tissue calcifications or ossifications based on a local administration of STS. The first results of this therapeutic strategy are highly promising and the local or systemic safety is satisfactory so far. These preliminary data also reported by others deserve to be confirmed in a prospective study.

We propose in this project to conduct a prospective open controlled phase II trial in order to assess the efficacy and the safety of intralesional administration of STS for the treatment of calcifications secondary to dermatomyositis or systemic sclerosis and ectopic ossifications secondary to pseudo-hypoparathyroidism 1a type (PHP1A/iPPSD2) (inactivating parathyroid hormone / parathyroid-hormone-related peptid (PTH/PTHrP) signalling disorder).

Inclusion Criteria:

• Patient presenting with:

  • ectopic ossification secondary to iPPSD2 or
  • ectopic calcification secondary to dermatomyositis or
  • ectopic calcification secondary to systemic sclerosis

• Patient aged 2 years or over

• Indication of STS infusion validated by a multidisciplinary committee, based on the significant morbidity and/or functional impact of the targeted calcification/ossification

• Patient with no planned surgery of the calcifications/ossifications for the twelve coming months

• Women of childbearing potential on highly effective contraception (such as hormonal contraception, intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner or sexual abstinence)

• Men with women of childbearing potential partners should use condoms during the whole treatment period and until 91 days after the last injection.

• Informed consent signed by the patient / parents

• Patient affiliated to the social security system

Exclusion Criteria:

• Allergy to STS or one of the excipients used
• Contraindication to local injection of STS
• Anticoagulant therapy
• Pregnant, parturient or breastfeeding woman
• Patient deprived of freedom by a court judgment or an administrative decision
• Patient undergoing psychiatric care under coercion
• Legally protected adult patients (guardianship / curatorship)
• Patient unable to give consent
• Patient placed under judicial protection