Ochronotic discoloration also can be detected on the nasal tip, costochondral junctions, extensor tendons of the hands, cheeks, fingernails, and buccal mucosa. Arthritic signs of ochronotic arthropathy develop in the third and fourth decades. The clinical discoloration of the skin is a result of formation of ochronotic pigment granules in the dermis, as well as in apocrine glands. Thus, the ochronotic changes of cartilaginous and tendonous structures are best appreciated in regions in which there is minimal thickness of the overlying skin, such as the ears, nasal tip and extensor tendons of the hands. Alkaptonuria is a genetic disorder due to a deficiency of an enzyme necessary to break down homogentisic acid.
Ochronotic pigmentation can also develop from medications.
Similar skin and cartilage alterations can be induced by quinacrine administration and at sites of quinine injections. Carbolic acid topical applications to cutaneous ulcers have also induced ochronotic skin alterations. Exogenous ochronosis has been reported with topical applications of phenol and hydroquinones to the skin. With exogenous ochronosis, the arthropathy seen with alkaptonuria does not occur. Most laboratory testing for alkaptonuria detect the alterations in the urine.