Oxalate is a naturally occurring compound found in many plants and is also produced as a waste product by the human body. Normally, it is dissolved and expelled through urine. When concentrations become too high, oxalate can bind with calcium to form microscopic, needle-like crystals. While known for causing kidney stones, these crystals can also deposit in other tissues. This article will explore oxalate crystal deposition in the skin, a manifestation that often signals an underlying systemic health problem.
The Formation of Oxalate Crystals in the Body
The body’s oxalate comes from two sources: absorption from certain foods and internal production by the liver as a metabolic byproduct. Healthy kidneys filter this compound from the blood and excrete it in the urine. A problem arises when the amount of oxalate in the blood becomes excessively high, a condition known as hyperoxaluria. When the kidneys are unable to clear the oxalate, its concentration in the bloodstream rises.
This state of oversaturation leads to systemic oxalosis, where calcium oxalate is no longer soluble and precipitates out of the blood. These solid crystals then deposit in tissues and organs. While the kidneys are the most affected organ, these deposits can accumulate in bone, heart muscle, blood vessels, and skin, leading to widespread organ damage. This deposition can trigger inflammation and fibrosis, which is the scarring and hardening of tissue. In blood vessels, the accumulation of sharp crystals can damage the vessel walls, leading to blockages and compromising blood flow.
Underlying Medical Conditions
The systemic deposition of oxalate crystals is driven by specific medical conditions that lead to hyperoxaluria. These causes are separated into two categories: primary and secondary. The root cause dictates the progression of the disease and the therapeutic strategies employed.
Primary hyperoxaluria (PH) is a group of rare, inherited metabolic disorders. These genetic conditions are caused by mutations in specific genes, such as AGXT, GRHPR, or HOGA1. When the enzymes made by these genes are deficient, the body cannot process a substance called glyoxylate properly and instead converts it into large amounts of oxalate. Primary hyperoxaluria type 1 (PH1) is the most common and severe form, often leading to kidney failure in childhood or early adulthood.
More commonly, systemic oxalosis results from secondary hyperoxaluria, which is an acquired condition. The most frequent cause is chronic kidney disease or end-stage renal disease (ESRD). As kidney function declines, the body loses its ability to excrete even normal amounts of oxalate, causing it to accumulate in the blood. Another cause is enteric hyperoxaluria, which stems from gastrointestinal disorders like Crohn’s disease or from procedures like gastric bypass surgery. These conditions can cause fat malabsorption, leading to excessive absorption of dietary oxalate.
Skin-Related Symptoms and Manifestations
When oxalate crystals deposit in the skin, they can produce a range of distinct symptoms. These dermatological signs tend to appear in advanced stages, particularly when kidney function is severely compromised.
A common skin finding is calcinosis cutis, which involves the formation of hard, insoluble nodules or papules under the skin’s surface that appear whitish or yellowish. Another manifestation is livedo reticularis, which presents as a mottled, purplish, net-like pattern across the skin. This pattern is caused by oxalate crystals lodging in the small blood vessels of the dermis, obstructing blood flow and making the vascular network visible.
In severe cases, vascular obstruction from crystal deposition can lead to more extreme symptoms. The skin can develop painful ulcers that are difficult to heal. In some instances, the lack of blood flow can result in tissue death, or gangrene. These skin symptoms are a clear indicator of advanced systemic oxalosis.
Diagnosis and Management
A definitive diagnosis of oxalate crystal deposition in the skin is made through a skin biopsy. During this procedure, a small sample of skin is removed and examined under a microscope. This allows a pathologist to identify the characteristic shape and structure of calcium oxalate crystals within the skin tissue and blood vessel walls.
Beyond a biopsy, clinicians use other tools to understand the scope of the problem. A 24-hour urine collection measures the total amount of oxalate being excreted, which helps confirm hyperoxaluria. Blood tests can assess kidney function and measure plasma oxalate levels. For individuals suspected of having a primary form of the disease, genetic testing is performed to identify the specific gene mutations.
Management of cutaneous oxalosis focuses on treating the underlying condition that causes high oxalate levels. Strategies include:
- Aggressive hydration to help dilute oxalate in the urine and encourage its excretion.
- High doses of pyridoxine (vitamin B6) for patients with PH1, which can be effective in reducing oxalate production in some cases.
- A strict, medically supervised diet low in oxalate-rich foods.
- Intensive hemodialysis for patients with kidney failure to filter oxalate from the blood.
- A combined liver and kidney transplant in the most severe cases of primary hyperoxaluria to correct both the enzyme deficiency and the organ failure.