Calciphylaxis is a rare, serious condition in which calcium builds up inside the walls of small blood vessels beneath the skin, cutting off blood flow and causing intensely painful skin wounds that can become life-threatening. It occurs most often in people with advanced kidney disease, particularly those on dialysis, but it can also develop in people with normal kidney function. The one-year mortality rate is roughly 40%, making early recognition critical.
How Calciphylaxis Damages the Skin
The core problem in calciphylaxis is calcium depositing in the middle layer of tiny arteries and arterioles, the smallest blood vessels that supply the skin and fat tissue. This calcification stiffens and narrows those vessels. On top of that, the inner lining of the blood vessels becomes injured, and small blood clots form inside them, further blocking flow. The combination of hardened walls and clotted channels starves surrounding tissue of oxygen, leading to tissue death and open wounds.
Your body normally produces proteins that keep calcium from settling into blood vessel walls. One of these, fetuin-A, works by binding calcium and phosphorus before they can crystallize in the wrong places. Another, called matrix Gla protein, also prevents vascular calcification but needs vitamin K to function properly. When these protective mechanisms fail or are overwhelmed, calcium deposits go unchecked.
Who Is Most at Risk
The strongest link is with end-stage kidney disease. Among people on chronic hemodialysis, the incidence is about 3.5 new cases per 1,000 patient-years. Rates appear to be even higher in people on peritoneal dialysis, with one study reporting 9.0 per 1,000 patient-years. In the German Calciphylaxis Registry, about 10% of all calciphylaxis patients had either normal kidney function or earlier-stage kidney disease that didn’t require dialysis, confirming this isn’t exclusively a dialysis complication.
Beyond kidney disease, several other factors raise risk:
- Warfarin use. One analysis found warfarin therapy was associated with a 10-fold higher risk. This likely relates to warfarin blocking vitamin K, which is needed for one of the body’s key anti-calcification proteins to work.
- Mineral imbalances. High blood phosphorus, high calcium levels, and overactive parathyroid glands all promote calcium deposition in vessels.
- Obesity. Calciphylaxis lesions tend to develop in areas with more fat tissue, and obesity is an independent risk factor.
- Female sex. Women are affected more frequently than men.
- Diabetes. A well-established contributing factor, likely because of the vascular damage diabetes causes.
- Low albumin levels. Low protein in the blood, often a sign of poor nutrition or chronic inflammation, appears in many cases.
- Corticosteroid use. Long-term steroid therapy has been identified as another medication-related risk.
What the Skin Changes Look Like
Calciphylaxis doesn’t start with open sores. The earliest sign is often livedo reticularis, a net-like, mottled purple or reddish discoloration of the skin. This can progress to firm, painful nodules or hardened plaques beneath the skin surface. Many people describe the pain as excruciating, often disproportionate to how the skin looks in early stages.
Without treatment, those areas break down into deep, necrotic ulcers covered by a thick black crust called eschar. Purpura (dark purple patches from bleeding under the skin) may also appear. The wounds most commonly develop on the thighs, abdomen, buttocks, and other areas with substantial fat tissue, though they can appear on the legs and other sites as well. These ulcers are extremely prone to infection, which is the leading cause of death in calciphylaxis patients.
How It Is Diagnosed
Diagnosis typically requires combining the clinical picture with a tissue sample. A standard punch biopsy, the small circular sample commonly taken in dermatology offices, often isn’t deep enough. Calciphylaxis affects vessels in the deeper layers of fat beneath the skin, so a deep incisional biopsy that captures the full thickness of skin and underlying tissue is needed.
Under the microscope, the hallmarks are calcium deposits within the walls of small and medium blood vessels, clots inside those vessels, and surrounding tissue death. If calcium deposits are absent on biopsy but the skin findings look similar, the diagnosis may instead be warfarin-induced skin necrosis, a condition that can closely mimic calciphylaxis. The two conditions share overlapping appearances, including similar rash patterns and locations, but warfarin skin necrosis results from a temporary clotting imbalance rather than vessel calcification.
Treatment Approaches
There is no single cure for calciphylaxis, and treatment involves addressing multiple factors simultaneously. The first priority is correcting mineral imbalances. For people on dialysis, this means intensifying dialysis sessions and adjusting phosphorus-lowering medications to bring calcium and phosphorus levels into a safer range. If parathyroid hormone levels are dangerously elevated, treating overactive parathyroid glands becomes part of the plan.
Any medications that may be contributing get reconsidered. Warfarin is typically stopped and replaced with an alternative blood thinner when possible, given its strong association with the disease.
The most widely used specific therapy is sodium thiosulfate, an intravenous compound that chelates (binds to) calcium, forming a more soluble salt that the body can clear more easily. It also has antioxidant properties that may help protect damaged tissue. For dialysis patients, the typical regimen is 25 grams given intravenously during or after hemodialysis sessions, three times per week. Treatment continues until wounds resolve, which can take months. The median number of infusions in published reports is 38, giving a sense of how prolonged treatment can be. The optimal dose has never been established through large controlled trials, and several attempted randomized studies of sodium thiosulfate were terminated before producing results.
Wound Care and Pain
Managing calciphylaxis wounds is one of the most challenging aspects of the condition. The ulcers are deeply painful, and dressing changes alone can cause significant distress. Dead tissue typically needs to be surgically removed through a procedure called debridement, sometimes followed by skin grafting once the wound bed is healthier. In some cases, hyperbaric oxygen therapy has been used to promote healing by delivering concentrated oxygen to damaged tissue.
Skin grafts, when used, are usually split-thickness grafts taken from another area of the body (often the thigh) and applied over the cleaned wound. Antimicrobial dressings help prevent the infections that these wounds are so vulnerable to. Negative pressure wound therapy, which uses suction to promote healing, isn’t always feasible because of the severe pain these patients experience and the difficulty of keeping the device in place on certain body areas.
Pain management itself is a major component of care. The pain from calciphylaxis is often described as among the worst patients have ever experienced, and it frequently requires strong pain medications to keep under control.
Survival and Outlook
Calciphylaxis carries a high mortality rate. In a French case-control study, about 40% of patients died within the first year of diagnosis, and 56% had died by five years. Infection from the open wounds is the most common direct cause of death, followed by complications of the underlying kidney disease. Patients whose lesions remain limited to areas with intact skin (without ulceration) generally have a better prognosis than those with open, ulcerated wounds.
A drug called SNF472 represents a newer approach. It works differently from sodium thiosulfate by directly blocking the formation and growth of calcium crystals inside blood vessel walls. In a Phase 2 trial of 14 dialysis patients with calciphylaxis, it improved wound healing, reduced pain, and was well tolerated with no serious treatment-related side effects. A Phase 3 trial (called CALCIPHYX) has been designed to test it in 66 hemodialysis patients with ulcerated lesions, comparing it against a placebo over 12 weeks.