A disorder due to inadequate dietary intake of niacin and/or tryptophan, manifested by a characteristic dermatitis on areas of the skin that are exposed to the sun, beginning as an erythema with pruritus that may lead to vesticulation but more frequently becomes chronic, rough, scaly, and hard with the formation of crusts as the result of haemorrhage; a broad band of this dermatitis frequently encircles the neck. The digestive tract and nervous system may be involved, with glossitis, stomatitis, gastroenteritis, diarrhoea with profuse watery and sometimes bloody stools, anxiety, depression, tremor, and reduced or absent tendon reflexes; encephalopathy may occur in severe cases. The disease is classically associated with a diet based on non-alkali-treated maize.

Synonyms: alpine scurvy; Casals collar (in part); Casals necklace (in part); chichism; disease of the 3 Ds; elephantiasis asturiensis; elephantiasis italica; erythema endemicum; Lombardy erysipelas; Lefula-pone (Lesotho); mayidism; niacinamidosis; niacin deficiency; pellagra sine pellagra; pseudopellagra (in part); psilosis pigmentosa; St Ignatius itch; typhoid pellagra (in part).

Notes.

1. The term “pseudopellagra” has been applied to pellagra occurring in those whose diet is not based on maize or millet, and “typhoid pellagra” has been applied to pellagra with sustained fever; both terms are deprecated. The typical band of dermatitis encircling the neck has been referred to as Casals collar or necklace (these terms are not recommended). The term “disease of the three Ds” (for dermatitis, diarrhoea, and dementia) is misleading since diarrhoea is not always present and dementia is relatively rare (though depression is common). On rare occasions pellagra may not show the characteristic dermatitis; this condition has been referred to by the confusing term “pellagra sine pellagra”.

2. The disorder may be secondary to certain other conditions, such as adrenal phaeochromocytoma and the administration of certain drugs (e.g. Isoniazid); in this case, the term “nicotinic acid deficiency due to...” is recommended.

Linguistic note. The name pellagra is derived from the Italian pelle agra, sharp [i.e., rough] skin.

Source: International nomenclature of diseases. Vol. IV. Metabolic, nutritional, and endocrine disorders. Geneva, World Health Organization, 1991, p. 279.