What is Ochronosis? ( 2 фото )

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Ochronosis is a rare metabolic disorder characterized by the **bluish-black or grayish-brown discoloration of connective tissues**, including cartilage, skin, and sclera (the white part of the eye). It occurs due to the accumulation of a dark pigment called **homogentisic acid (HGA)**.
There are two main types:
**Endogenous (Alkaptonuric) Ochronosis:** The classic, inherited form.
**Exogenous Ochronosis:** Acquired from external sources.
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Endogenous Ochronosis (Alkaptonuria)
This is the genetic basis of the condition.
* **Cause:** A mutation in the **HGD gene**, leading to a deficiency of the enzyme **homogentisate 1,2-dioxygenase**.
* **Biochemical Defect:** The body cannot properly break down the amino acids **tyrosine and phenylalanine**. This causes a buildup of homogentisic acid (HGA) in the body.
* **What Happens:** The excess HGA polymerizes (forms chains) and binds to collagen in connective tissues, creating a blue-black pigment. This process is called **ochronosis**. The same HGA is also excreted in urine, causing it to darken upon standing or alkalization—a key diagnostic sign called **alkaptonuria**.
Symptoms & Progression:
The disease is often silent for decades. Symptoms typically appear in **adulthood (30s-40s)** and progress.
* **Early Sign:** Darkening of urine on a diaper or when left standing.
* **Skin & Eye Discoloration:**
* **Eyes:** Gray or blue-black pigmentation in the sclera (most notably near the insertion of the rectus muscles).
* **Skin:** Bluish discoloration in areas with cartilage, like the ears, nose, and cheeks. Sweat may also stain clothes brown.
* **Musculoskeletal Problems (Major Cause of Disability):**
* **Severe, early-onset osteoarthritis,** especially in the spine (called **ochronotic spondylosis**). The spine can appear calcified and rigid on X-ray.
* Pain and stiffness in large joints (knees, shoulders, hips).
* Tendon and ligament calcification.
* **Pigmented, brittle cartilage** that can lead to ruptures (e.g., tendons, intervertebral discs).
* **Other Organ Involvement:**
* **Cardiac:** Pigmentation of heart valves (aortic and mitral) and vessels, leading to stenosis, calcification, and a risk of coronary artery disease.
* **Renal & Prostate:** Pigment can lead to kidney stones and prostate stones.
Diagnosis:
* **Urine Test:** The simplest test. HGA is detected in urine (it turns dark with alkaline pH or on a test strip).
* **Genetic Testing:** Confirms mutations in the *HGD* gene.
* **Imaging:** X-rays show characteristic calcification and degeneration of the spine and joints.
* **Specialized Tests:** Liquid chromatography to quantify HGA in urine or plasma.
Treatment (Management):
There is **no cure**, but treatment focuses on slowing progression and managing symptoms.
* **Nitisinone:** A medication that inhibits the production of HGA, significantly reducing its levels in the body. It's the primary disease-modifying therapy.
* **High-Dose Vitamin C:** An antioxidant that may theoretically slow the oxidation and deposition of HGA, though evidence is limited.
* **Pain Management:** Analgesics, physical therapy, and joint rehabilitation.
* **Surgical Intervention:** Joint replacements (hip, knee) and, in severe cases, heart valve surgery may be necessary.
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Exogenous Ochronosis
This is an acquired form caused by prolonged exposure to certain substances.
* **Cause:** Most commonly from the **long-term topical use of hydroquinone-containing skin lightening creams**. It can also rarely be caused by phenol exposure, antimalarials, or chronic use of resorcinol.
* **Mechanism:** The substance inhibits the enzyme (homogentisate oxidase), causing a local accumulation of HGA-like pigments in the dermis.
* **Symptoms:**
* **Skin:** Asymptomatic blue-black or gray-brown hyperpigmentation, typically in areas where the cream was applied (cheeks, temples, neck). It may also present as tiny "caviar-like" papules.
* It does **not** involve the eyes, internal organs, or joints like the endogenous form.
* **Treatment:** **Discontinuation of the offending agent** is crucial. The pigmentation is often permanent, but treatments like lasers (Q-switched) may offer some improvement, though with risk of worsening.
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Key Takeaway
Ochronosis is a vivid example of how a single enzyme defect (or external chemical inhibition) can have widespread, progressive effects on the body's structural tissues. **Endogenous ochronosis is a systemic disease affecting joints, heart, and vision**, while **exogenous ochronosis is primarily a skin condition** resulting from topical agents like hydroquinone.


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