Background Calcinosis is caused by accumulation of calcium salts in the tissues, with subcutaneous nodules, atrophy and ulceration over the affected area. Treatment with intravenous sodium thiosulfate has been used, since it inhibits the precipitation of calcium salts and dissolves calcium deposits. Recently, cases successfully treated with topical 10–25% sodium thiosulfate have been described.

Purpose To analyse the efficacy and safety of topical treatment with a formulation of 10% sodium thiosulfate in a paediatric patient with iatrogenic calcinosis.

To optimise the preparation of the formulation.

Results To achieve greater occlusivity that allowed adequate absorption and a greater pharmacological effect, a topical W/O emulsion was prepared using a commercial product (’cold cream’) as the oily external phase. It was necessary to dissolve the hydrophilic drug in water prior its incorporation in the external phase.

The clinical response to treatment was prompt, gradually reducing visible injuries, subcutaneous calcifications, induration and swelling. After 15 days, the pain disappeared completely and mobility was recovered with the help of rehabilitation. The calcified material was gradually expelled as calcium crystals through ulcers over three months.

Tolerance of the cream was adequate, with slight temporary pruritus in the first month.

The stored emulsion remained stable for 4 months.

Conclusions Topical treatment with a W/O emulsion of 10% sodium thiosulfate was effective, as in the published literature (although in one case the concentration was 25% and in the other one injuries were only subcutaneous) and well tolerated (without topical or systemic adverse reactions).

Despite the low compatibility between the ionic drug and ‘cold cream’, the emulsion was stable at least 4 months.

No conflict of interest.