Pellagra is a symptom complex which results from concomitant deficiencies of niacin, riboflavin, and pyridoxine.  Multiple organ systems are affected and this disorder manifests as a rash on sun exposed areas, mild hyperpigmentaion, diarrhea, glossitis, nausea, vomiting, postprandial discomfort, cognitive dysfunction, memory deficits, insomnia, anxiety, depression, fatigue, acute psychosis, seizures, ataxia, mucous membrane inflammation, and spastic paraparesis.  Pellagra may be a complication of isoniazid therapy and carcinoid tumors.  The diagnosis is established by the history, physical exam, and response to therapy (niacin 100-500 mg PO BID, pyridoxine 50-100 mg PO QD, plus riboflavin) because there are no reliable readily available tests to measure niacin levels.  The typical patient is a homeless, alcoholic patient who does not have access to regular nutritional meals or declines access to these meals in favor of continued alcohol consumption.