Metastatic Calcification
Metastatic calcification (metastatic calcinosis cutis) is a serious disorder of mineral deposition in the skin and soft tissues. Dystrophic calcification forms in tissue that is already damaged or necrotic; metastatic calcification is different, because calcium phosphate crystals precipitate directly into completely healthy skin. The trigger is a long-standing systemic imbalance: high blood calcium, high blood phosphate, or an abnormal calcium–phosphate product.
These deposits can be painful, limit movement and ulcerate, leaking a chalky discharge over long periods. Just as importantly, they are a warning sign of a serious endocrine or metabolic disease, such as end-stage chronic kidney disease, secondary hyperparathyroidism or vitamin D toxicity.
At Haute-Derma, we map the deposits in detail with high-frequency ultrasound (HFUS) and combine crystal-dissolving medical therapy (sodium thiosulfate, STS) with laser and minimally invasive procedures. The aim is to break down the deposits, relieve pressure on surrounding tissue and preserve the skin as well as possible.
Definition and Pathogenesis
The Physical Chemistry of Crystal Precipitation
- Calcium–phosphate product (Ca × P): in healthy people, plasma calcium multiplied by plasma phosphate is about 35–40 mg²/dL². When high calcium or phosphate pushes this product past the physiologic saturation point of > 55 mg²/dL² (and especially above 70 mg²/dL²), the blood becomes supersaturated.
- Hydroxyapatite formation: free calcium and phosphate ions combine into hydroxyapatite microcrystals that settle directly into:
- The collagen and elastin framework of the dermal extracellular matrix.
- Subcutaneous fat and joint capsules.
- The basement membranes of small arteries and capillaries beneath the skin.
- Preferred sites: metastatic calcification favors tissues with a slightly alkaline local environment (from acid loss or active proton pumping), including the skin and soft tissue around large joints, renal tubules, alveolar walls of the lungs and the gastric mucosa.
Underlying Causes
A raised systemic Ca × P product leading to metastatic calcification usually stems from one of five groups of conditions:
- End-Stage Kidney Disease (ESRD / CKD Stage 5):
- Reduced phosphate excretion in the urine → high blood phosphate.
- Less calcitriol made by the kidneys → poorer intestinal calcium absorption → sustained compensatory PTH secretion and secondary/tertiary hyperparathyroidism, which drives heavy bone resorption and releases calcium and phosphate into the circulation.
- Primary Hyperparathyroidism: usually a benign parathyroid adenoma that overproduces PTH, increasing bone breakdown and calcium reabsorption in the renal tubules.
- Vitamin D Toxicity / Calcitriol Overuse: maximizes absorption of calcium and phosphate from the gut and increases mineral release from bone into the blood.
- Bone Destruction From Malignancy: multiple myeloma, lymphoma or widespread bone metastases release factors that stimulate bone resorption, causing an acute rise in blood calcium.
- Milk-Alkali Syndrome: caused by long-term intake of large amounts of calcium carbonate together with alkali.
Clinical and Imaging Features
Skin and Soft Tissue Findings
- Papules and Subcutaneous Nodules (Tumoral Calcinosis): rock-hard lumps, only slightly tender or painless, usually symmetric. They most often sit in the soft tissue around large weight-bearing or high-use joints (elbows, hips, knees, shoulders) or on the fingertips.
- White Chalky Discharge: as deposits grow, they compress the blood supply to the overlying epidermis, which can break down and form a draining tract. The discharge is a thick, cloudy paste resembling chalk or cream, packed with calcium phosphate microcrystals.
- Uremic / Hypercalcemic Itch (Uremic Pruritus): patients often have persistent, widespread itching as calcium microcrystals lodge in the upper dermis and irritate C-fiber nerve endings.
Role of Imaging and Lab Tests
- Blood Tests: raised total/ionized calcium and raised phosphate. PTH is high in hyperparathyroidism and low in vitamin D toxicity.
- High-Frequency Ultrasound (HFUS 20–50 MHz) at Haute-Derma: deposits show up as bright, strongly echogenic bands with clean acoustic shadowing in the dermis or subcutaneous fat, which clearly separates them from lipomas or fibromas.
Comparing Common Types of Soft Tissue Calcification
| Metastatic Calcification | Dystrophic Calcification | Calciphylaxis |
|---|---|---|
| Markedly raised Ca × P > 55 | Normal | Markedly raised Ca × P > 55 |
| Completely healthy tissue | Previously necrotic, inflamed or scarred tissue | Calcium in the walls of small arteries and in fat |
| End-stage kidney disease, hyperparathyroidism, vitamin D toxicity | Scleroderma, dermatomyositis, lupus, old scars | Kidney failure on dialysis, tertiary hyperparathyroidism |
| Around large joints; organs (kidney, lung, stomach) | Fingers, pressure points, old scars | Fatty areas (buttocks, thighs, abdomen, lower legs) |
| Limited movement, risk of draining infection | Slowly progressive, mainly local pain | Dermatologic emergency: vessel occlusion, gangrene |
Multimodal Treatment at Haute-Derma
Our core goal at Haute-Derma is to bring the Ca × P product back into the physiologic range (< 45–50 mg²/dL²) so that new deposits stop forming, while dissolving existing crystals locally and relieving pressure on the tissues.
Controlling the Systemic Metabolic Imbalance
- Non-Calcium Phosphate Binders:
- Sevelamer carbonate (800–1,600 mg by mouth with meals) or lanthanum carbonate.
- Contraindicated: calcium-based phosphate binders (such as calcium acetate and calcium carbonate) should not be used, as they worsen calcium supersaturation.
- Calcimimetics:
- Cinacalcet (30–90 mg/day) activates the calcium-sensing receptor (CaSR) on the parathyroid glands, lowering serum PTH without raising blood calcium or phosphate.
- Optimizing Dialysis: we work with the dialysis team to lower the dialysate calcium concentration to 1.25 mmol/L.
Dissolving Calcium Crystals With Sodium Thiosulfate (STS)
- How it works: STS reacts with insoluble calcium phosphate to form calcium thiosulfate, which is about 250 times more water-soluble and is cleared more easily by dialysis or in the urine.
- How We Use It at Haute-Derma:
- Intravenous infusion: 12.5–25 g IV at the end of each dialysis session (three times a week).
- Intralesional STS: a standardized STS solution is injected around small subcutaneous deposits to dissolve the crystals on the spot.
Laser and Surgical Options
- UltraPulse CO2 Laser Micro-Channels: the CO2 laser creates tiny channels through the compressed skin so the chalky material can drain out safely, easing tissue pressure and speeding healing.
- Surgical Removal of Large Deposits: considered when a deposit is large enough to compress nerves or vessels, seriously restricts joint movement, or has ruptured and become secondarily infected.
