Ochronosis – Causes, Symptoms and Treatment
Ochronosis is a rare condition characterized by the deposition of dark bluish-black pigments in connective tissue, cartilage, and skin. It can be hereditary or triggered by external substances.
Things worth knowing about "Ochronosis"
Ochronosis is a rare condition characterized by the deposition of dark bluish-black pigments in connective tissue, cartilage, and skin. It can be hereditary or triggered by external substances.
What is Ochronosis?
Ochronosis is a medical condition marked by the abnormal accumulation of dark ochronotic pigments in various body tissues. The term is derived from the Greek word ochros (yellowish), although the deposited pigments typically appear bluish-black in tissue. Two main forms are distinguished: endogenous ochronosis, which occurs as a consequence of the rare inherited metabolic disorder alkaptonuria, and exogenous ochronosis, which results from prolonged external application of certain substances to the skin.
Causes
Endogenous Ochronosis (Alkaptonuria)
Endogenous ochronosis is a complication of alkaptonuria, an autosomal recessively inherited metabolic disorder. In this condition, the enzyme homogentisate 1,2-dioxygenase is absent or deficient, leading to the accumulation of homogentisic acid – a breakdown product of the amino acids phenylalanine and tyrosine. This acid is oxidized and polymerized into dark ochronotic pigments that deposit in connective tissue, cartilage, tendons, and internal organs.
Exogenous Ochronosis
Exogenous ochronosis is caused by the long-term topical use of certain substances. Common triggers include:
- Hydroquinone (found in skin-lightening creams)
- Phenol and phenolic compounds
- Resorcinol
- Certain antimalarial drugs (e.g., chloroquine)
- Carbolic acid
This form is especially prevalent in regions where skin-lightening products are widely used, including parts of Africa and Asia.
Symptoms
Skin and Visible Signs
- Bluish-grey or brownish discoloration of the skin, especially on the face (cheeks, nose bridge)
- Dark spots and papules (small raised skin lesions)
- Thickening and rough texture of affected skin areas
- In alkaptonuria: blue-black discoloration of the sclerae (whites of the eyes), ears, and nasal tip
Internal Organs and Joints (in Endogenous Ochronosis)
- Ochronotic arthropathy: pain and stiffness in large joints (spine, knees, hips) due to pigment deposits in cartilage
- Heart valve involvement: pigment deposits on heart valves can lead to cardiac complications
- Kidney stones caused by homogentisic acid deposits
- Dark discoloration of urine (a hallmark sign of alkaptonuria)
Diagnosis
Diagnosis of ochronosis involves a combination of clinical examination and laboratory tests:
- Clinical examination: assessment of typical skin discolorations and other visible signs
- Urine analysis: in alkaptonuria, urine darkens upon exposure to air (indicating the presence of homogentisic acid)
- Laboratory testing: measurement of homogentisic acid in urine by chromatography
- Skin biopsy: microscopic analysis of a tissue sample to confirm pigment deposits – particularly in exogenous ochronosis
- Dermoscopy: non-invasive skin examination using a dermoscope
- Genetic testing: detection of mutations in the HGD gene when alkaptonuria is suspected
Treatment
Endogenous Ochronosis (Alkaptonuria)
For a long time, no causal treatment for alkaptonuria was available. Since 2020, nitisinone (Orfadin) has been approved in Europe as a treatment option. Nitisinone inhibits the production of homogentisic acid, thereby slowing disease progression. Additional management strategies include:
- Dietary modification: reduction of phenylalanine and tyrosine intake (low-protein diet)
- High-dose vitamin C (ascorbic acid) to slow pigment formation
- Physiotherapy and pain management for joint complaints
- Joint replacement surgery (endoprostheses) in cases of severe arthropathy
Exogenous Ochronosis
- Immediate discontinuation of the causative substance (e.g., hydroquinone-containing creams)
- Laser treatments (e.g., Q-switched laser) to reduce discoloration
- Chemical peeling or dermabrasion
- Sun protection to prevent worsening of pigmentation
Prognosis
The prognosis of ochronosis depends largely on its cause. In the exogenous form, significant improvement can be achieved after discontinuing the triggering substance. Endogenous ochronosis associated with alkaptonuria is a lifelong condition, but its progression can be positively influenced by early treatment with nitisinone. Regular medical follow-up is strongly recommended.
References
- Phornphutkul C, Introne WJ, Perry MB et al. - Natural history of alkaptonuria. New England Journal of Medicine, 2002; 347(26): 2111-2121.
- Eißing L, Schoen MP - Exogenous ochronosis. Deutsches Ärzteblatt International, 2019.
- European Medicines Agency (EMA) - Orfadin (nitisinone): European Public Assessment Report, 2020. Available at: https://www.ema.europa.eu
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