Case of the Month

A 57-year-old woman presents with progressive darkening of her cheeks. She was told that she had melasma and she has been using an 'unknown lightening cream' she purchased at the Somali cultural store for the past 3 years on the areas. Upon examination of a crumpled tube of the cream in her purse it was noted that it contained hydroquinone.

What's Your Diagnosis?

Diagnosis: Exogenous Ochronosis

Dermatopathologic examination (100X) reveals classic exogenous ochronosis, a variation of induced cutaneous alkaptonuria. Congenital alkaptonuria is the absence of homogentisic acid oxidase. the earliest symptom is dark/black colored urine in babies. Later in life, congenital alkaptonuria can cause arthritic and cardiac problems. The exact cause of the skin darkening is still unknown but it has been postulated to be the result of the topical hydroquinone's (chronic) inhibition of homogentisic acid oxidase in the local area. The accumulated homogentisic acid then polymerizes to form the ochronotic pigment that appears as the yellow/brown banana-shaped structures seen here. This can also occur with the use of antimalarials and products that contain resorcinol, phenol, mercury, or picric acid. Treatment is difficult but may improve with certain lasers.

(Dermatopathologic micrographs of this case courtesy of Erick Jacobson, MD.)