Acute Intermittent Porphyria



Acute intermittent porphyria is a disease marked by an enzyme deficiency

Pathophysiology of acute intermittent porphyria

1) type of hepatic hemoglobinopathy (hepatic porphyria)
2) caused by decrease levels of HMB synthase (PBG deaminase)
3) classic subtype – enzyme defect occurs in erythrocytes
4) variant subtype – enzyme defect is in nonerythrocyte tissues
5) has highly variable clinical course
6) occurs episodically when activated by one or more precipitating factors
7) precipitating factors are hormones, drugs, diet, stress (e. g. infections, surgery), alcohol, low-calorie diet

Signs and Symptoms

1) gastrointestinal – abdominal pain, ileus, distention, nausea, vomiting, constipation, diarrhea
2) autonomic – sweating, hypertension, dysuria, urinary retention, black-colored urine
3) muscular/skin – pain in extremities, neck and torse and hirsuitism (thought to be the disease state that gave rise to the werewolf legends
4) neurologic – peripheral motor neuropathy (usually affects arms and shoulders first), headache, seizures
5) psychiatric – anxiety, depression, paranoia, and hallucinations

Characteristic Test Findings

Laboratory – 1) increased ALA and PBG in both serum and urine 2) hyponatremia 3) black-colored urine EKG – 4) arrhythmias

Histology/Gross Pathology

neuropathy is caused by axonal degeneration (not demyelinization)

Associated Conditions

partial list of drugs that precipitate attacks:

barbituates
alcohol
sulfonamides
meprobamate
carbamazepine
valproic acid
glutethimide
phenytoin
estrogens
danazol

Inheritance/Epidemiology

1) autosomal dominant
2) more common in Great Britain and Scandinavia

Treatment

1) heme infusion (hematin, heme albumin, or heme arginate
2) avoidance of precipitating factors
3) long-acting gonadotropin-release hormone analog

Tips for USMLE

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