Pellagra is a disease of deficiency of niacin (vitamin B3) which causes problems in the skin and the digestive and nervous system and can mimic rosacea.
Pellegra -
Image - derma.freehostia.com
There is at least one report that a patient was initially diagnosed with rosacea and it turned out to be pellegra.
Pellegra - Image A.D.A.M.
More info on rosacea mimics
