Causes and risk factors
There are two types of ochronosis: a) endogenous and b) exogenous. Endogenous – ochronosis is a genetically inherited disorder. It is inherited in an autosomal recessive pattern. There is inadequate production of enzyme called as homogentisic acid oxidase. This is responsible for breakdown of homogentisic acid, which is a toxic byproduct of tyrosine metabolism. Thus incomplete metabolism of homogentisic acid, tyrosine, and phenylalanine causes the disease. Maximum amount is excreted in urine, but some remains in the body and gets deposited in connective tissues and cartilages and converts into pigmented polymeric material. Exogenous – Long term usage of skin lightening products can lead to the disease. Chemicals like hydroquinones, phenols, mercury, benzene, etc., are additional risk factors.
Clinical presentation
Patient presents with Brown grey or black hyperpigmentation. The pigmented lesions will be seen more on the part of body which is most exposed to sun. Narrowing of joint spaces and calcification occurs. Cornea of eye also becomes hyperpigmented. Sclera shows bluish black pigmentation. There is darkening and hardening of ear cartilage or nasal cartilage. Stiffening of ribs occurs. Hardening of tissues of heart can also take place. Discoloration of urine [alkaptonuria] is seen in early childhood. Eyelids, cheek, axilla, nail beds, are some of the other skin manifestations.
Investigations
Medical history by the patient and clinical examination by the doctor helps in diagnosis. Lab tests like urine test will show elevated levels of HGA [homogentisic acid]. Synovial fluid examination from the affected bone can also be helpful. Imaging studies such as radiography, MRI may be useful for further evaluation.
Treatment
There is no specific line of treatment, but good protein rich diet is advocated whereas complete replacement or removal of tissues is also possible. Vitamin C is proved useful which slows down the conversion of homogentisic acid into pigmented polymeric material. Hence small doses of vitamin C will also help in managing the disease. Exogenous ochronosis is treated with laser.
Complications
Complications such as cardiovascular diseases or arthropathy can occur.
When to Contact a Doctor
One must consult a doctor if there is evidence of dark urine or hyperpigmentation.
Prevention
Avoiding topical phenols, avoiding food low in tyrosine prevents the disease.
Systems involved
Digestive system [metabolism], integumentary system, musculoskeletal system
Organs involved
Skin, tissues, cartilages, bones, eyes