Pellagra occurs with the lack of intake of vitamin B3, produced by a deficiency in the intake of it.
A dermatologist is a doctor who specializes in diseases of the skin, hair, nails and mucous membranes.
A doctor or family doctor is responsible for diagnosing and prescribing medical treatments to patients. The family doctor refers to patients where a specialist when a specific treatment is required.
Remember that for the proper selection of health professional that treats pellagra you must consider the nature, severity and symptoms you are presenting.