Porphyrias are metabolic disorders that affect the biosynthesis of heme (a component of hemoglobin) and cause excessive production and excretion of porphyrins or their precursors. Porphyrins, which are present in all protoplasm, figure prominently in energy storage and utilization. Classification of porphyrias depends on the site of excessive porphyrin production; they may be erythropoietic (erythroid cells in bone marrow), hepatic (in the liver), or erythrohepatic (in bone marrow and liver). (See Types of porphyria.) An acute episode of intermittent hepatic porphyria may cause fatal respiratory paralysis. In the other forms of porphyrias, the prognosis is good with proper treatment.
Porphyrias are inherited as autosomal dominant traits, except for Günther’s disease (autosomal recessive trait) and toxic-acquired porphyria (usually from ingestion of or exposure to lead). Menstruation often precipitates acute porphyria in premenopausal women.
Porphyrias are generally marked by photosensitivity, acute abdominal pain, and neuropathy. Hepatic porphyrias may produce a complex syndrome marked by distinct neurologic and hepatic dysfunction:
❑ Neurologic symptoms include chronic brain syndrome, peripheral neuropathy and autonomic effects, tachycardia, labile hypertension, severe colicky lower abdominal pain, and constipation.
❑ During an acute attack, fever, leukocytosis, and fluid and electrolyte imbalance may occur.
❑ Structural hepatic effects include fatty infiltration of the liver, hepatic siderosis, and focal hepatocellular necrosis.
❑ Skin lesions may cause itching and burning, erythema, and altered pigmentation and edema in areas exposed to light. Some chronic skin changes include milia (white papules on the hands’dorsal aspects) and hirsutism on the upper cheeks and periorbital areas.
Other laboratory values may include increased serum iron levels in porphyria cutanea tarda; leukocytosis, syndrome of inappropriate antidiuretic hormone, and elevated bilirubin and alkaline phosphatase levels in acute intermittent porphyria.
Treatment for porphyrias includes avoiding overexposure to the sun and using beta-carotene to reduce photosensitivity, as well as support for acute and long-term management. Hemin (an enzyme-inhibitor derived from processed red blood cells) is given to control recurrent attacks of acute intermittent porphyria, Günther’s disease, variegate porphyria, and hereditary coproporphyria. A high-carbohydrate diet decreases urinary excretion of ALA and PBG, with restricted fluid intake to inhibit release of antidiuretic hormone.
❑ Warn the patient to avoid excessive sun exposure, use a sunscreen when outdoors, and take a beta-carotene supplement to reduce photosensitivity.
❑ Encourage a high-carbohydrate diet.
❑ Administer beta-carotene and hemin, as ordered.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
» Next page: Porphyrias (Handbook of Diseases)
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