Are there any metabolic disorders associated with nonmelanin skin dyspigmentation?

Yes. Ochronosis (alkaptonuria) is a rare autosomal recessive inherited deficiency of homogentisic acid oxidase that results in accumulation of homogentisic acid in connective tissue, where it causes a dark brown to bluish-gray dyspigmentation. Commonly affected skin areas include the pinna, tip of the nose, sclera, extensor tendons of the hands, fingernails, and tympanic membranes. Less commonly, blue macules develop on the central face, axillae, and genitalia.

Homogentisic acid also is deposited in the bones and articular cartilage, causing ochronotic arthropathy that results in premature degenerative arthritis. Overall, the course of ochronosis is progressive dyspigmentation and articular degeneration with no successful treatment available.