Differences between the various types of soft tissue calcifications
• Calcinosis cutis: calcium deposits form in the skin (see Question 33).
• Calciphylaxis: calcification occurs in the intima of blood vessels and subcutaneous tissue. This is primarily seen in patients with chronic renal failure, uremia, and a high calcium/phosphorous product (>70). This frequently presents with ischemia and skin ulceration. Treatment is to control the hyperphosphatemia and uremia. In severe cases, IV sodium thiosulfate has been used.
• Tumoral calcinosis: large calcific nodules in juxtaarticular locations causing pain and limited range of motion. There are three types: primary hyperphosphatemic, primary normophosphatemic, and secondary tumoral calcinosis. The primary hyperphosphatemic subtype is autosomal recessive and tends to affect adolescents and young adults. The basic defect is thought to be in the proximal renal tubular cell with an elevated renal phosphate reabsorption threshold and increased production of 1,25-dihydroxyvitamin D. Mutations of the GALNT3, KLOTHO, and FGF23 genes have been described. Notably fibroblast growth factor (FGF) 23 is an important phosphaturic hormone. Mutations that cause inactivation of FGF 23 cause hyperphosphatemia. Treatment is inadequate and includes low-phosphate diet, phosphate-binding antacids, acetazolamide, and surgical excision. The tumoral calcinosis tends to recur after surgical removal. The primary normophosphatemic subtype may be due to mutations of the SAMD9 gene that is important in cellular apoptosis. It is unclear how this causes tumoral calcinosis. Secondary tumoral calcinosis is usually due to chronic renal failure with secondary or tertiary hyperparathyroidism and is treated by subtotal parathyroidectomy or renal transplantation.
• Heterotopic ossification: abnormal formation of lamellar bone within soft tissues such as tendons, ligaments, or muscles. It commonly occurs in patients with traumatic brain injuries or spinal cord injuries. Patients with these neurologic problems as well as patients with diffuse idiopathic skeletal hyperostosis (DISH) or ankylosing spondylitis are at risk for developing this following total joint arthroplasty. Patients have pain and a limited range of motion. Patients at high risk should receive indomethacin, IV bisphosphonates, or local radiation therapy before arthroplasty to prevent this complication. Recurrence is common after surgical removal.