Acute intermittent porphyria

Posted by e-Medical PPT Saturday, August 13, 2011
The Porphyrias
Group of inherited or acquired disorders of heme production

Classification of the Porphyrias
Multiple ways to categorize porphyrias:
Hepatic vs. Erythropoietic: Organ in which accumulation of porphyrins and their precursors appears
Cutaneous vs. Non- cutaneous
Acute and non-acute forms

Acute:
Aminolevulinate dehydratase deficiency porphyria (ALA-D)
Acute intermittent porphyria (AIP)
Hereditary coproporphyria (HCP)
Variegate porphyria (VP)

Chronic:
Porphyria cutanea tarda (PCT)
Erythropoietic protoporphyria (EPP)
Ccongenital erythropoietic porphyria (CEP)
Hepatoerythropoietic porphyria (HEP)

Acute intermittent porphyria
The prevalence of AIP in the United States is thought to be 5–10 per 100 000.
 It is more common in northern European countries, such as Sweden (60–100 per 100 000), Britain and Ireland.
Acute intermittent porphyria PBGD gene mutation is inherited in an autosomal dominant fashion.
 The enzyme activity is 50% of normal in those who inherit the genetic trait.
 There is no difference in PBGD activity between patients and latent gene carriers.
 An inherited deficiency of PBGD is not in itself sufficient to cause clinical expression of AIP; the great majority ( 90%) of individuals who inherit a deficiency of PBGD never develop porphyric symptoms.
 More than 200 mutations of the PBGD gene have been described to date in AIP.
Affects women more than men, with a ratio of 2:1.
Most patients become symptomatic at age 18-40 years.
 Attacks occurring before puberty or after age 40 years are unusual unless a major provocation
Most patients are completely free of symptoms between attacks.
Course of the neurological manifestations is highly variable.
 Acute attacks of porphyria may resolve quite rapidly.
 Sudden death may occur, presumably due to cardiac arrhythmia.

Symptoms
Most patients are completely free of symptoms between attacks
Attacks involve neuro-visceral symptoms but no skin manifestations:
 The sequence of events in attacks usually is (1) abdominal pain, (2) psychiatric symptoms, such as hysteria, and (3) peripheral neuropathies, mainly motor neuropathies.
Gastroenterological Symptoms most common:
 Constipation (48–84%), colicky abdominal pain (occurring in 85–95% cases), vomiting (43–88%), diarrhea (5–12%)
 The abdominal pain is severe and lasts for several days. Severe abdomen pain of short (<1 d) duration or chronic abdominal pain is unusual.
Patients may have CNS signs consisting of seizures (10–20%), mental status changes, cortical blindness, and coma.

Precipitants
Drugs: most common precipitate of acute attacks :
Barbiturates and sulphonamides being most common
Reduced energy intake:  even brief periods of starvation during dieting, postoperative periods, or concurrent illness.
Tobacco smoke: polycyclic aromatic hydrocarbons, are known inducers of hepatic cytochrome P450 enzymes and heme synthesis.
An association between cigarette smoking and repeated attacks of porphyria was found in a survey of 144 patients with AIP in Britain (Lip et al, 1991).
Infections, surgery and stress.

Diagnosis
Urinary ALA and PBG are always markedly increased in symptomatic patients with AIP and even in some asymptomatic individuals with the inherited enzyme deficiency
PBG in urine is oxidized to porphobilin upon standing, which gives a dark-brown color to urine, and often referred to as ‘port-wine reddish urine’.

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