Endogenous ochronosis: when clinical suspicion prevails over histopathology.

Endogenous ochronosis (EO) or alkaptonuria is an inherited autosomal recessive disease caused by the insufficiency of the enzyme homogentisic acid dioxygenase. This disturbance causes an accumulation and increased renal excretion of homogentisic acid (AHG), which manifests as dark urine when it oxidizes on contact with air. Other clinical manifestations of OE are the result of the deposit of AHG in the form of ochronotic pigment at the level of collagen in the skin and cartilage, where it causes blue-gray cutaneous hyperpigmentation, degenerative arthropathy, valvular disease, and other multisystem effects. Despite the progressive and irreversible nature of OE and the lack of a curative treatment, the life expectancy is preserved. We report a new case of EO with cutaneous and joint involvement, in which a high clinical suspicion, confirmed by elevated AHG in urine was the key in the diagnosis.