Efficacy of Sodium Thiosulfate in Shoulder Pain in Calcific Tendinitis of the Rotator Cuff

Calcific tendinitis of the rotator cuff is one of the most common causes of shoulder pain. It is characterized by calcium phosphate crystal deposition in the rotator cuff. Its pathogenesis and etiology remains unclear and the mechanisms leading to this pathological mineralization are still largely unknown. This disorder can lead to a chronic pain during daily or professional activities and to a restriction of range of motion. During the disease, spontaneous resorption can occur with migration of apatite crystals into the subacromial bursa causing severe pain and restriction of movement. Factors associated with the development of symptoms are still unclear although the size and presence of a bursitis on imaging have been shown to be associated with pain.

Ultrasound guided percutaneous lavage (UGPL or barbotage or irrigation) of calcific tendinopathy is indicated when conservative treatments (physiotherapy, nonsteroidal anti-inflammatory drugs) have failed. At this stage, extracorporeal shock wave therapy (ESWT) or subacromial corticosteroid injection can also be discussed. However, a recent network meta-analysis has shown that UGPL could be the treatment of choice compared to the other nonsurgical options such as ESWT or SAI. Arthroscopic removal of the calcific deposit is considered as a second line therapy after failure of UGPL or EWST.

Efficacy of UGPL depends on the type of calcification. Calcific deposits can be differentiated in hard calcifications, usually dense on X-Ray with an acoustic shadow on US, and soft calcifications, with more heterogeneous or faint contours without acoustic shadowing. Some studies observed failure only in patients presenting with a dense and homogeneous calcification type A according to the Molé Classification and also showed that outcome after needling and/or ESWT will be worse in case of dense calcifications, with only 30% of success compared to 61% in patients with soft calcification. These failures are most of the time explained by the persistence of the calcific deposit. In line with this, was found a positive correlation between the decrease of the size of the calcification and the pain score over time; as the calcification became smaller, the pain became less intense.

Several approaches are currently used to facilitate the extraction of the calcification. It has been shown that lavage with warm saline heated at 42°C reduced the procedure duration and improved calcification dissolution. Another randomized controlled study recently reported that lavage with a 2 needle approach also shortened the procedure in hard calcification. However, none of these studies showed an impact on the rate of calcification elimination. Other strategies are therefore needed to treat hard calcification of the rotator cuff.

Sodium thiosulfate (STS) (Na2S2O3) is primarily used to prevent and treat cyanide poisoning. Intravenous STS is also used off-label to treat calciphylaxis leading to a significant decrease of soft-tissue and vascular calcifications. However, its systemic use may be limited by adverse effects, such as gastrointestinal upset, metabolic acidosis, and sodium overload. Thus, alternative local approaches have been developed. Recent reports have shown the interest of topical STS in the treatment of calciphylaxis, tumoral calcinosis associated with connective tissue disease, pseudohypoparathyroidism or hyperphosphatemic familial tumoral calcinosis. For instance, a daily application of topical STS on the calcific lesions of patients with hyperphosphatemic familial tumoral calcinosis led to their decrease after 5 months of treatment. Topical application of STS has also showed an anti-inflammatory effect in patients with calcinosis cutis secondary to connective tissue disease and radiodermatitis. Because deeper calcific deposits are unlikely to be reached by topical therapeutic agents, some authors performed intralesional STS injections in patients with localized cutaneous calciphylaxis. They observed a complete healing of ulcers and remission of disease with only transient localized discomfort during injection. Despite these promising results, the exact mechanisms by which STS is able to dissolve ectopic calcifications remain still unclear.