Pellagra is a disease caused by a deficiency of niacin in the diet, affecting ectodermal tissues such as the skin, gastrointestinal tract, and nervous system. Its clinical manifestations include dermatitis, diarrhea, and dementia.

bubble_chart Etiology

Niacin is an essential component of two important intermediate metabolic coenzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), and is involved in the metabolism of carbohydrates, fats, and proteins, which is necessary for cellular oxidation-reduction. Niacin is synthesized in the human body from tryptophan via the kynurenine pathway, so a deficiency of tryptophan in the diet or diseases affecting tryptophan metabolism can lead to niacin deficiency. Chronic alcoholism, thyrotoxicosis, fever, gastrointestinal dysfunction, and certain substances chemically similar to niacin, such as isoniazid, compete with niacin, rendering it unavailable for use by the body, all of which may be related to niacin deficiency. It is well known that populations relying on corn or sorghum as staple foods are prone to this disease (previously called pellagra), as these foods contain high levels of leucine, which may interfere with tryptophan metabolism. It has also been suggested that toxins secreted by Fusarium fungi, commonly found in moldy grains, are related to the condition, and this has been confirmed in animal experiments. Additionally, elevated levels of coproporphyrin in urine have been observed, which is associated with photosensitivity, and sun exposure can trigger skin lesions.

bubble_chart Clinical Manifestations

This disease primarily affects the skin, gastrointestinal tract, and nervous system. The typical symptoms are dermatitis, diarrhea, and dementia, collectively known as the 3D syndrome. However, the simultaneous presence of all three is relatively rare.

1. Dermatitis: This is valuable for diagnosis. Skin lesions commonly occur in areas exposed to sunlight or subjected to friction and pressure, presenting symmetrically on the face, back of the hands, wrists, neck, chest, and dorsum of the feet. Initially, the lesions appear bright red with well-defined borders, resembling sunburn, and may or may not have blisters, accompanied by a burning sensation and cutaneous pruritus. After weeks or months, the lesions darken to a deep red, reddish-brown, or brownish-black hue, with rough, scaly surfaces. Prolonged cases may exhibit atrophy. Wrist lesions are more pronounced on the radial side than the ulnar side. Nasal lesions are distinctive, with the bridge showing dark red patches accompanied by grade I powdery scaling. Neck and chest lesions often form a collar or necklace-like pattern around the neck. The condition typically worsens in summer, subsides in winter, and recurs every spring.
   Mucosal lesions may manifest as redness, swelling, and pain of the tongue, with early fungiform papillae swelling followed by flattening and atrophy. Aphthous ulcers, pharyngitis, and angular cheilitis may occur. The vulva can also be affected, presenting with labial redness and swelling, as well as vaginitis.
2. Gastrointestinal symptoms: Primarily involve the esophagus, stomach, and colon, often featuring diarrhea, occasionally with mucous or bloody stools. Other symptoms include loss of appetite, indigestion, nausea, vomiting, abdominal distension, and abdominal pain.
3. Neurological symptoms: May include neurasthenic manifestations such as dizziness, blurred vision, lack of strength, insomnia, memory impairment, and mental fatigue. Psychiatric symptoms like depression, cognitive decline, hallucinations, delusions, mania, and dementia may also occur. Peripheral neuropathy can present as limb numbness, muscle weakness, diminished or absent tendon reflexes, and, rarely, myelitis.

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bubble_chart Diagnosis

Based on dermatitis, gastrointestinal symptoms, and psychiatric symptoms, combined with medical history, laboratory tests, and the significant effectiveness of niacin treatment, the diagnosis is not difficult to establish.

bubble_chart Treatment Measures

1. Avoid sun exposure and maintain a balanced diet with high-protein and niacin-rich foods, such as fresh green leafy vegetables, legumes, eggs, milk, meat, and animal liver.
2. Administer nicotinamide 200–500 mg daily for several weeks depending on the severity of the condition, along with vitamin B complex. For severe cases, intramuscular or intravenous injection of nicotinamide 500 mg/d may be required.
3. Provide symptomatic topical treatment for skin and mucous membrane lesions.