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Calciphylaxis is a condition characterised by necrosis (cellular death) of the skin and fatty tissue. It is seen mainly in patients with end stage kidney disease. It is also sometimes called calcific uraemic arteriolopathy.

In 1981, approximately 50 cases of calciphlaxis were reported in the world literature. Today, the incidence is estimated at 1 percent per year in patients undergoing dialysis. The mortality is extremely high, up to 80%, often within several months of onset. The primary cause of death is from secondary infection of the ulcers, and sepsis.

How does calciphylaxis occur?

The cause of calciphylaxis is not properly understood. Calcification blocks small blood vessels deep in the skin, resulting in spreading skin necrosis (tissue death).

Small blood vessels become blocked with blood clots, which leads to the black painful necrotic areas. It is thought that the clots occur because of calfication within the walls of the blood vessels.

In chronic renal failure, it is often associated with a condition known as secondary hyperparathyroidism. The damaged kidneys don't excrete phosphate properly, which results in a build up of phosphate in the blood, which combines with calcium. Vitamin-D levels are reduced because of the kidney failure and reduced absorption through the gut. The bones become resistant to parathyroid hormone. The parathyroid glands therefore increase in size and produce more hormone increasing the amount of calcium circulating in the blood.

Calciphylaxis can occur in those with high or normal levels of serum calcium and phosphate, with or without vitamin D replacement, in dialysed patients and less often in those who have not yet commenced dialysis or in those who have received a renal transplant. It is more common in women than in men, in obese patients compared to those of normal weight, and in patients who have been taking corticosteroids or other immunosuppressive medicines.

Calciphylaxis can also occur in patients with normal kidney function, in the presence of hypercoagulability states. These may include liver disease, diabetes and treatment with warfarin. High levels of matrix metalloproteinases have been described and one theory suggests chemically altered elastin protein allows deposition of calcium on small vessels.

Clinical features of calciphylaxis

Calciphylaxis begins as surface purple-coloured mottling of the skin (retiform purpura) then bleeding occurs within the affected area. There may be blood-filled blisters. The skin goes black in the centre of star-shaped (stellate) purple lesions. The skin cells die because of lack of blood supply (dry gangrene). This causes deep and often extensive ulcers.

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Patients with calciphylaxis usually experience severe pain, burning and sometimes itching at the lesion sites.

Calciphylaxis most often occurs on the lower limb especially in fatty areas. Lesions on the trunk, abdomen, buttocks or thighs, appear to be more dangerous than lesions on the lower legs and feet.

Risk factors for calciphylaxis

Certain conditions in addition to renal failure are associated with accelerated calcium deposition in soft tissues:

How is the diagnosis made?

A deep wedge skin biopsy may be necessary to diagnose calciphylaxis as a similar appearance can be seen in other conditions such as necrotising fasciitis, cryoglobulinaemia, antiphosopholipid syndrome, coumarin necrosis and vasculitis. The pathologist looks for calcium deposited within scarred and blocked blood vessels in the subcutaneous tissue. There may also be inflammation of the fat (panniculitis).

Xrays of the affected limb may demonstrate vascular calcification within the skin; however this may also be seen in healthy patients with renal disease who are not affected by calciphylaxis.

Management of calciphylaxis

The best treatment for calciphylaxis is not yet clear.

The initial step is to normalise the calcium and phosphate product levels, and control the hyperphosphatemia associated with renal failure. A calcium and phosphate restricted diet and dialysis with a lower diasylate calcium concentration is important initial management in the calciphylaxis associated with renal failure.

In patients with significantly elevated parathyroid hormone that cannot be medically controlled, surgical removal of the parathyroid glands (parathyroidectomy) is thought to reduce pain and promote wound healing, especially in early wound development. Parathyroidectomy should not be performed in calciphylaxis in the absence of hyperparathyroidism, as it can result in low levels of calcium in the blood and bone disease. Cinacalcet tablets can also be used to reduce secondary hyperparathyoidism.

Some patients may also be treated with anticoagulants to reduce the tendency to form blood clots, but these are not always suitable or helpful. Warfarin can be replaced by heparin in some cases.

Meticulous wound management is important.

Intravenous infusions of sodium thiosulfate, an antioxidant and chelator, has also been used successfully to remove the calcium. Healing occurs slowly over weaks to months.

Etidronate, a biphosphonate, has been reported of benefit, but biphosphonates may not be suitable for patients on haemodialysis.

Inhibitors of matrix metalloproteinases such as doxycycline have been reported to prevent new lesions forming.

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Author: Dr Fiona Larsen MB ChB, Dept of Dermatology Greenlane Hospital Auckland

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