# Calciphylaxis in Renal Disease

## Introduction

Calciphylaxis, also known as calcific uremic arteriolopathy, is a rare and life-threatening condition characterized by calcification of dermal and subcutaneous arterioles that leads to ischemic skin necrosis. It occurs predominantly in patients with end-stage renal disease (ESRD) but can also arise in non-uremic settings. The mortality rate is extremely high, making early recognition and aggressive multidisciplinary management essential.

## Epidemiology

The incidence is 1 to 4% of dialysis patients per year, with mortality reaching 60 to 80% at one year and a median survival of approximately six months from diagnosis. Death is primarily from sepsis arising from infected wounds. Risk factors include female sex (2-3:1 ratio), obesity (BMI greater than 30), diabetes mellitus, warfarin use (which inhibits matrix Gla protein carboxylation, a key calcification inhibitor), elevated calcium-phosphorus product (greater than 70 mg2/dL2), hyperparathyroidism, hypoalbuminemia, protein C and S deficiency, calcium-based phosphate binders, vitamin D analogues such as calcitriol, and corticosteroid use.

## Pathophysiology

### Vascular Calcification

The disease involves medial calcification of small dermal and subcutaneous arterioles measuring 40 to 600 micrometers. Vascular smooth muscle cells undergo osteochondrogenic transformation, expressing bone matrix proteins including osteocalcin, osteopontin, and BMP-2. Elevated phosphorus drives vascular calcification through activation of Pit-1 transporters on smooth muscle cells, creating a calcium-phosphorus imbalance. Matrix Gla protein (MGP), a vitamin K-dependent calcification inhibitor, is functionally blocked by warfarin, which prevents its carboxylation and removes a critical brake on vascular calcification. Fetuin-A, a circulating calcification inhibitor, is reduced in uremia. NF-kB activation promotes osteogenic differentiation and endothelial dysfunction. Progressive arteriolar narrowing ultimately leads to thrombosis, tissue ischemia, and infarction.

<image>Histopathologic diagram of calciphylaxis showing a small dermal arteriole with medial calcification (von Kossa positive), intimal fibroplasia, luminal thrombosis, and surrounding fat necrosis with calcification of subcutaneous adipose tissue and overlying epidermal necrosis</image>

## Clinical Features

### Cutaneous Findings

Early lesions present as exquisitely painful, indurated plaques with livedo reticularis or retiform purpura. These progress to violaceous discoloration evolving into black necrotic eschars with surrounding erythema. Distribution is important prognostically: proximal lesions involving the thighs, abdomen, and buttocks carry a worse prognosis than distal lesions on the legs and digits. Proximal and truncal involvement accounts for approximately 60% of cases in dialysis patients. Wounds are often bilateral and symmetric. Pain is characteristically severe and disproportionate to the visible lesion, especially early in the disease course.

### Non-Uremic Calciphylaxis

Calciphylaxis can occur in patients without ESRD, associated with primary hyperparathyroidism, alcoholic liver disease, malignancy, connective tissue disease, warfarin use even without renal disease, and obesity. The pathophysiology likely involves the same osteochondrogenic transformation of vascular smooth muscle cells.

## Diagnosis

### Clinical Suspicion

Any dialysis patient with exquisitely painful retiform purpura or necrotic skin lesions should be evaluated for calciphylaxis. Clinical diagnosis is often sufficient when the presentation is classic.

### Skin Biopsy

Biopsy is confirmatory but carries risk of wound non-healing, pathergy, and infection. Specimens should be taken from the edge of a lesion rather than the necrotic center and must include subcutaneous fat. Punch biopsies of 4 to 6 mm may be insufficient, and incisional biopsy is preferred to sample deep subcutaneous vessels. Histology reveals medial calcification of small arterioles (demonstrated with von Kossa and alizarin red stains for calcium), intimal fibroplasia, luminal thrombosis, subcutaneous fat necrosis with calcification, and septal panniculitis. Some experts recommend avoiding biopsy altogether if the clinical picture is classic, given the risk of wound complications.

### Laboratory Evaluation

The workup includes calcium, phosphorus, and calcium-phosphorus product, intact PTH level, albumin (hypoalbuminemia is a poor prognostic sign), coagulation studies including protein C, protein S, and antithrombin III, alkaline phosphatase (often elevated), and INR to assess warfarin use.

### Imaging

Plain radiography may show calcification of subcutaneous vessels in a net-like or pipe-stem pattern. Nuclear bone scan with technetium-99m demonstrates increased uptake in soft tissues and subcutaneous areas. While sensitive but not specific, bone scanning is useful for monitoring treatment response.

| Risk Factor | Mechanism/Contribution |
|-------------|----------------------|
| ESRD/Dialysis | Uremic milieu; reduced fetuin-A; Ca-P imbalance |
| Warfarin | Inhibits matrix Gla protein carboxylation (calcification inhibitor) |
| Obesity (BMI >30) | Adipose tissue calcification; pannicular vessel involvement |
| Elevated Ca×P product (>70) | Drives vascular calcification via Pit-1 transporters |
| Hyperparathyroidism | Increases calcium mobilization |
| Calcium-based phosphate binders | Increases serum calcium load |
| Hypoalbuminemia | Poor prognostic marker; reduced calcification inhibition |
| Diabetes mellitus | Vascular disease predisposition |
| Female sex (2-3:1) | Unknown mechanism |
| Protein C/S deficiency | Promotes thrombosis in calcified arterioles |

## Management

### Multidisciplinary Approach

Effective management requires collaboration between dermatology, nephrology, wound care, nutrition, pain management, and surgery.

### Wound Care

Meticulous wound care involves debridement of necrotic tissue, though aggressive surgical debridement should be approached cautiously as it may extend wounds. Non-adherent dressings and moist wound healing principles apply. Infection prevention and treatment are paramount because wounds are highly susceptible to superinfection, and sepsis is the leading cause of death.

### Metabolic Correction

Warfarin must be discontinued immediately and replaced with a non-vitamin K-dependent anticoagulant such as heparin or a DOAC if anticoagulation is needed. Calcium-based phosphate binders should be switched to non-calcium alternatives such as sevelamer or lanthanum. Dialysis should be intensified with increased frequency (daily or longer sessions) using low-calcium dialysate to reduce the calcium-phosphorus product. Cinacalcet, a calcimimetic agent, addresses secondary hyperparathyroidism by reducing PTH, calcium, and phosphorus. Vitamin D analogues that increase the calcium-phosphorus product should be avoided. Parathyroidectomy is considered for severe hyperparathyroidism refractory to medical management, though it is controversial and carries high surgical risk.

### Sodium Thiosulfate (STS)

Sodium thiosulfate is the first-line pharmacologic therapy alongside metabolic correction. The dose is 25 grams IV in 100 mL normal saline over 30 to 60 minutes, administered during the last 30 minutes of each hemodialysis session, typically three times per week. Its mechanisms include chelation of calcium, increasing calcium solubility, acting as an antioxidant and vasodilator, and inhibiting adipocyte calcification. Side effects include metabolic acidosis, nausea and vomiting (which may be severe), hypotension, and volume overload. Treatment continues for weeks to months until wound healing is evident. The evidence base consists of case series and retrospective studies, with no randomized controlled trials available.

<image>Treatment algorithm for calciphylaxis management showing immediate interventions (stop warfarin, stop calcium-based binders, start STS), metabolic targets (lower Ca-P product below 55, PTH control with cinacalcet), wound care strategies, and pain management approaches</image>

### Pain Management

Pain is often severe and debilitating, requiring multimodal analgesia. Opioids are frequently necessary and should be titrated to comfort. Gabapentinoids address the neuropathic pain component, with doses adjusted for renal function. Low-dose IV or intranasal ketamine is an option for refractory pain. Non-pharmacologic approaches include wound care optimization and psychological support.

### Emerging and Adjunctive Therapies

Bisphosphonates such as pamidronate and etidronate inhibit vascular calcification through a pyrophosphate analogue mechanism, with case reports showing benefit. Tissue plasminogen activator (tPA) addresses the thrombotic component but has very limited evidence. Hyperbaric oxygen therapy may improve tissue oxygenation in ischemic wounds, again with limited evidence. SNF472, also known as myo-inositol hexaphosphate or IP6, is a selective calcification inhibitor that showed promise in clinical trials for vascular calcification.

## Prognosis

Proximal and truncal lesions carry a worse prognosis than distal lesions, and ulcerated lesions fare worse than non-ulcerated ones. Mortality predictors include proximal location, large wound size, non-healing despite treatment, hypoalbuminemia, and elevated alkaline phosphatase. Kidney transplantation may improve calciphylaxis in selected patients by correcting the uremic milieu. Even with optimal treatment, many patients succumb to sepsis or withdrawal of care due to refractory pain.

## Clinical Pearls

Calciphylaxis should be suspected in any dialysis patient presenting with exquisitely painful retiform purpura or necrotic skin lesions. Warfarin is a major modifiable risk factor and should be discontinued immediately with a switch to an alternative anticoagulant. Sodium thiosulfate IV during dialysis is the cornerstone of pharmacologic treatment. Biopsy must include deep subcutaneous tissue to identify the characteristic arteriolar calcification, as superficial biopsies may miss the diagnostic findings. Sepsis from wound infection is the leading cause of death, making aggressive wound care and infection surveillance paramount.

## References

1. Nigwekar SU, Thadhani R, Brandenburg JG. Calciphylaxis. *N Engl J Med*. 2018;378(18):1704-1714.
2. McCarthy JT, El-Azhary RA, Patzelt MT, et al. Survival, risk factors, and effect of treatment in 101 patients with calciphylaxis. *Mayo Clin Proc*. 2016;91(9):1252-1260.
3. Hayden MR, Tyagi SC, Kolb L, et al. Vascular ossification-calcification in metabolic syndrome, type 2 diabetes mellitus, chronic kidney disease, and calciphylaxis-calcific uremic arteriolopathy: the emerging role of sodium thiosulfate. *Cardiovasc Diabetol*. 2005;4:4.
4. Nigwekar SU, Kroshinsky D, Nazarian RM, et al. Calciphylaxis: risk factors, diagnosis, and treatment. *Am J Kidney Dis*. 2015;66(1):133-146.