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Pellagra

Pellagra is a caused by nicotinic acid (niacin) deficiency. The classical features are the 3 D's - dermatitis, diarrhoea and dementia.

Pellagra may occur as a consequence of isoniazid therapy (isoniazid inhibits the conversion of tryptophan to niacin) and it is more common in alcoholics.

Features

  • dermatitis (brown scaly rash on sun-exposed sites - termed Casal's necklace if around neck)
  • diarrhoea
  • dementia, depression
  • death if not treated

Questions

  1. A 60-year-old man is admitted to hospital with acute pneumonia. He has a past medical history of chronic obstructive pulmonary disease, alcohol excess and hypertension, and has been homeless for the last 12 years. On the post-take ward round, you notice that he has a brown-red discolouration of his face, neck, forearms and lower legs, with scaling and cracking of the skin. He complains that he is struggling to eat and drink and has persistent vomiting and diarrhoea. He seems a little disorientated. Which vitamin deficiency is most likely to be causing these symptoms?

a. [B2 (riboflavin)3%] b. [B3 (niacin)83%] c. [B6 (pyridoxine)3%] d. [B1 (thiamine)9%] e. [B12 (cyanocobalamin)3%]

Deficiency of niacin (B3) causes pellagra

The correct answer is B3- niacin. The patient has some of the symptoms of pellagra, which is classically characterised by the triad of dermatitis, diarrhoea and dementia. The 'dementia' more commonly presents subtly with low mood, irritability, apathy and anxiety, progressing to delusions, psychosis, drowsiness and coma.

DermNet NZ:
https://www.dermnetnz.org/topics/pellagra/