[Answered]: Marcus is a long-standing patient of your free clinic

Marcus is a long-standing patient of your free clinic. He has lived with alcoholism for many years, but has managed to keep his job and a place to live. You have not seen him for a while, so looked forward to catching up with him when you see that he has scheduled a visit. When walking into the room to perform your assessment, you notice that all skin where his skin has been exposed to the sun is darkly pigmented. You find that Marcus has not only lost his job, but is now unhoused and spends most of his day outside of the shelter where he sleeps at night. You suspect the health provider will diagnose pellagra. What is pellagra and what causes this skin disorder? Why is Marcus at risk of this skin disorder?