Ochronosis: Causes, Symptoms, and Treatment

Ochronosis is a bluish-black tissue pigmentation due to the deposition of oxidation products of homogentisic acid (HGA) or related polymers. The phenomenon occurs in two clinically distinct contexts: alkaptonuria (a rare congenital metabolic disorder known as "endogenous" ochronosis) and localized skin lesions following prolonged use of bleaching agents containing hydroquinone and other phenols ("exogenous" ochronosis). Correct differentiation is crucial because diagnosis and treatment differ. [1]

Briefly about the types

• Endogenous (alkaptonuria, AKU): autosomal recessive deficiency of the HGD enzyme → accumulation of HGA in fluids and tissues → over time, "ochronotic" pigment in cartilage, tendons, skin, and intervertebral discs, as well as characteristic urine that turns black when standing. Ochronotic arthropathy develops after 30-40 years. [2]
• Exogenous: bluish-black/slate hyperpigmentation of the face (cheeks, cheekbones) and sometimes the neck in people who have used creams with hydroquinone for a long time (especially >4% and months-years), less often - with phenol/resorcinol, mercury, picric acid, antimalarial. [3]

Causes and pathogenesis

Alkaptonuria (AKU). Homogentisate 1,2-dioxygenase (HGD) deficiency disrupts the tyrosine breakdown pathway. HGA oxidizes and polymerizes, forming an "ochronotic" pigment that "grows" into collagen-rich tissues (ear cartilage, sclera, intervertebral discs), staining them brittlely and causing structural damage. [4]

Exogenous ochronosis. Long-term topical exposure to hydroquinone (and a number of other phenols) causes local inhibition of enzymatic pathways and deposition of ochronotic pigment in the dermis (banana-shaped yellow-brown granules on histology). The risk is higher at concentrations >4%, prolonged use, and high sun exposure. [5]

Symptoms

Alkaptonuria/endogenous ochronosis

• Early marker: darkening of urine when exposed to air/alkaline solution. Over time, bluish-black discoloration of the ear cartilages, sclera at the limbus ("Osler sign"), and grayish-blue skin over the cartilages. [6]
• From the 3rd decade - ochronotic arthropathy: pain and stiffness in the spine and large joints; X-rays/CT scans show disc calcification and narrowing of the joint spaces. Kidney/prostate stones are common. [7]

Exogenous ochronosis

• Symmetrical blue-gray or black-brown spots/plaques on the cheekbones, forehead, and sometimes the neck; often "granular" dermal pigmentation, resistant to conventional bleaching agents. Itching/pain is usually absent. [8]

Diagnostics

If you suspect alkaptonuria (AKU)

1. Urine: Homogentisic acid (HGA) measurement - by GC-MS/HPLC (gold standard). In some laboratories, simple chemical tests (e.g., ferric chloride - transient blue/violet color) are used for "screening." [9]
2. Genetics: Search for HGD variants for confirmation and family counseling. [10]
3. Visualization: X-ray/CT of the spine and large joints (calcification of discs, apophyses), echocardiography/ultrasound of the kidneys as indicated. [11]

If you suspect exogenous ochronosis

1. History: long-term use of hydroquinone creams (often over-the-counter), phenol/resorcinol, “lightening cosmetics”, high sun exposure. [12]
2. Dermoscopy/biopsy (if indicated): dermal "banana-shaped" granules of ochronotic pigment; but with a typical picture and obvious exposure, clinical examination is often sufficient. [13]

Table 1. Endogenous vs. exogenous ochronosis - key differences

Sign	Endogenous (AKU)	Exogenous
Cause	Hereditary HGD deficiency → HGA excess	Long-lasting hydroquinone/phenols on skin
Localization	Systemic: cartilage, sclera, discs, skin	Local: usually face/neck
Early sign	"Blackening" urine when standing/alkalinizing	Gradual bluish-black hyperpigmentation
Confirmation	HGA in urine (GC-MS), HGD gene	Dermal biopsy (if necessary), anamnesis
Treatment	Nitisinone, symptom control, orthopedics	Completely abolish HQ, sunscreen, lasers/retinoids

[14]

Treatment

Endogenous ochronosis (alkaptonuria)

1. Nitisinone (NTBC) 10 mg/day blocks the formation of HGA "upstream," sharply reducing its levels in urine/serum and slowing progression; studies (SONIA 2 and subsequent observations) have shown a reduction in signs of ochronosis and clinical benefit. Tyrosinemia monitoring (Tyr elevation - class effect) and ophthalmologic examination are required. Dietary restriction of Tyr/Ph e is often used to manage tyrosine. [15]
2. Symptom and complication management: NSAIDs/physiotherapy, injections for joint pain, and endoprosthetics for severe arthropathy; nephro- and urological management of stone formation; cardiac monitoring as indicated. Ascorbic acid has been used historically, but there is no convincing benefit on outcomes. [16]
3. Monitoring: regular pain and function assessment, HGA/Tyr, ophthalmologist, nephro-/cardiac monitoring. [17]

Exogenous ochronosis

1. Immediately stop using hydroquinone and any other irritants; strict photoprotection (SPF 50+, hats). This is a must. [18]
2. Medicinal and cosmetic support: topical retinoids, azelaic acid; long-term therapy, moderate effect. [19]
3. Treatments (as indicated in an experienced center): Q-switched Nd:YAG 1064 nm, fractional lasers/peels, sometimes microneedling. Results are variable; multiple sessions are required; post-inflammatory hypopigmentation is possible - inform the patient. [20]

Table 2. Nitisinone for alkaptonuria: what is important to know

Question	Short answer
Effect	Reduces HGA, slows ochronosis/arthropathy
Dose	More often than 10 mg/day (according to SONIA 2 data)
Security control	Blood tyrosine, corneal examination (risks of hypertyrosinemia)
Additionally	Consider a Tyr/Ph e restricted diet to control tyrosine

[21]

Differential diagnosis (hints)

• Argyria (silver), blue nevus, hemochromatosis/melasma, Addison's disease, hemosiderosis – with cutaneous pigmentation. An exposure history and dermatoscopy are helpful.
• For systemic cartilage/scleral "blueness" and arthropathy, consider AKU first and check for HGA in urine. [22]

Frequently Asked Questions (FAQ)

• Is it possible to cure exogenous ochronosis with creams?

Completely – rare. The basic treatment is to stop using hydroquinone and protect yourself from the sun. Retinoids and lasers can partially lighten the lesions, but the course is long and the results are variable. [23]

• Does Nitisinone stop alkaptonuria?

It radically reduces HGA and slows tissue damage; don't expect a complete reversal of long-term changes. Long-term use and tyrosine/corneal monitoring are required. [24]

• How can you quickly tell if a patient has AKU?

Ask about darkening of urine on exposure to air, look at ear cartilage/sclera, do HGA in urine (or at least ferric chloride test until confirmed). [25]