Porphyrias
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 use. 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.
Causes
Porphyrias are inherited as autosomal dominant traits, except for Günther’s disease (autosomal recessive trait) and toxic-acquired porphyria (usually from the ingestion of or exposure to lead). Menstruation commonly precipitates acute porphyria in premenopausal women.
Signs and symptoms
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 signs and 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 dorsal aspects of the hands) and hirsutism on the upper cheeks and periorbital areas.
