| • | = the clinical syndrome of niacin (vitamin B3) deficiency |
| • | etiology: deficiency of niacin or its precursor tryptophan body can synthesize niacin from tryptophan(an amino acid) |
Tryptophan à Niacin à NAD ßàNADP
clinical:
| • | redness and superficial scaling; photodistributed |
| • | the change resemble sunburn and subside leaving a dusky, brown-red discoloration |
| • | circumferential dermatitis of the neck: Casal’s necklace (sometimes more like brooch than a necklace) |
| • | mnemonic: the 3 D’s Dementia, Dermatitis, Diarrhea |
| • | ddx: drug eruptions, porphyrias, actinic reticuloid |
| • | within 24 hours after niacin therapy is begun, the skin lesions begin to resolve, confirming the diagnosis |
treatment:
| • | nicotinic acid (niacin) IV |
| • | niacinamide PO (less flushing than with PO niacin) |
causes:
| • | malnutrition (associated classically with a diet almost entirely composed of corn) |
| • | carcinoid tumor (tryptophan consumed by serotonin production) |
| • | isoniazid (competes biochemically with niacin owing to a close structural resemblance) |
| • | Hartnup’s disease (genetic defect in transport of neutral amino acids including tryptophan across brush border epithelium of intestine and kidney) |
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