Pellagra

Description and cause

Pellagra is a nutritional deficiency state, caused by a lack of niacin (Vitamin B3, nicotinamide) or tryptophan (an amino acid). The most common cause is therefore a dietary deficiency.

Vitamins are substances that are essential in small quantities but cannot be made by humans: they therefore must be obtained from food sources. Good sources of niacin include yeast, meats, cereals, legumes and seeds.

Dietary tryptophan not needed for protein production can be converted into niacin. Some estimate that up to 50% of daily niacin comes from tryptophan conversion. If diet is deficient in Vitamin B3 and not enough conversion can occur from tryptophan, a deficiency will result.

Recommended daily requirements of niacin are:

• Males: 20mg niacin or 1200mg tryptophan
• Females: 15mg niacin or 900mg tryptophan

Other possible causes:

Carcinoid syndrome: In this condition, tryptophan is metabolized to 5-OH tryptophan and serotonin, instead of to niacin. This can lead to pellagra.

Isoniazud therapy: When used for long periods, this anti-tuberculosis drug can cause a niacin deficiency. Patients on this drug are usually also prescribed niacin to prevent this.

Hartnup disease: This is a congenital disorder resulting in defective absorption of tryptophan, so that less of it is available for conversion to niacin.

Symptoms

The most characteristic finding is a rash, similar in appearance to sunburn, on the exposed parts of the skin. Other symptoms are

• Glossitis – a smooth, reddened tongue
• Painful mouth, leading to refusal of food
• Diarrhoea and vomiting
• Sensitivity to sunlight
• Weakness
• Headache
• Mental confusion and irritability
• Peripheral neuropathy
• Insomnia
• Dementia and encephalopathy in extreme cases
• Seizures and coma

Diagnosis

The diagnosis of pellagra is clinical – findings on examination together with details of the patient’s diet are usually clear enough.

Treatment

Treatment is with adequate doses of niacin, usually in the form of niacinamide, up to 500mg daily, depending on the severity of the illness and the response of the patients. A common side effect is facial flushing, which may be quite uncomfortable at first, but can be minimised by using slow-release forms of niacin.

Outcome

Providing the missing vitamin reverses the symptoms and signs of pellagra, and ingesting the normal daily amounts will prevent recurrences.

Dr AG Hall

The information provided in this article was correct at the time of publishing. At Mediclinic we endeavour to provide our patients and readers with accurate and reliable information, which is why we continually review and update our content. However, due to the dynamic nature of clinical information and medicine, some information may from time to time become outdated prior to revision.