Hyperpigmented Skin Patches

A 70-year-old man presents to an urgent care center after becoming concerned about brown hyperpigmented patches on his legs and arms. He says that he thinks some of his teeth are turning gray, but it has been happening so slowly that he is not sure. He reports that he has been in good health recently, especially after starting to take antibiotics last year to treat his rheumatoid arthritis.
View the image taken (Figure 1) and consider what your diagnosis would be.