Ochronosis

Ochronosis
Homogentisic acid
Classification and external resources
Specialty	endocrinology
ICD-10	E70.2 (ILDS E70.230)
ICD-9-CM	270.2
DiseasesDB	409
eMedicine	derm/476
MeSH	D009794
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Ochronosis is a syndrome caused by the accumulation of homogentisic acid in connective tissues. It was first described by Rudolf Virchow in 1865. The condition was named after the yellowish (ocher-like) discoloration of the tissue seen on microscopic examination. However, macroscopically the affected tissues appear bluish grey because of a light-scattering phenomenon known as the Tyndall effect. The condition is most often associated with alkaptonuria but can occur from exogenous administration of phenol complexes like hydroquinone.

There are two types of ochronosis: endogenous and exogenous. The endogenous variety is an autosomal recessive disease, that is caused by a lack of homogentisate oxidase enzyme. Exogenous ochronosis is an avoidable dermatitis, that can be caused by the topical application of compounds such as hydroquinone or phenols. It was first seen in 1912, when a patient who used phenol on a leg ulcer was found by Beddard and Plumtre to have this condition. Hydroquinone-induced exogenous ochronosis was found in 1975 by Findlay, who observed the condition in patients who used skin lightening creams containing the compound.

There are three clinical stages of exogenous ochronosis:

Exogenous ochronosis can be caused from long-term usage of certain "skin lightening" products, even if the hydroquinone is in amounts as small as 2%. Skin lightening products are still prevalent in many parts of the world. This may be due to aesthetic or social standing reasons, in areas where a lighter skin tone is considered to be a sign of wealth or beauty. As well, skin-lightening creams containing compounds such as hydroquinone are commonly used to help with hyperpigmentation disorders such as melasma.

Hydroquinone is the compound most frequently used in skin whitening products. Due to concerns about its side effects, it was almost banned by the FDA in 2006, as there were medical issues of carcinogenicity and reports of disfiguring ochronosis. In the European Union hydroquinone has been banned in cosmetic creams since 2000.

Long-term use of creams containing this compound may lead to exogenous ochronotic lesions. The duration of the use is directly proportional to the risk of developing the condition with most cases being after years of use. Around 10–15 million skin lightening products are sold annually, with Japan being the major buyer.

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