Acute Intermittent Porphyria
Acute intermittent porphyria, which causes abdominal pain and neurologic symptoms, is the most common acute porphyria.
Many people never experience symptoms.
Symptoms may include vomiting, abdominal or back pain, weakness in arms or legs, and mental symptoms.
Laboratory tests are done on urine samples taken during the attack.
Maintaining good nutrition and avoiding alcohol and drugs that trigger attacks are important.
Attacks are treated by giving glucose and sometimes heme.
Acute intermittent porphyria occurs in people of all ethnic groups. In most countries, it is the most common of the acute porphyrias. Other acute porphyrias include
Variegate porphyria and hereditary coproporphyria also cause skin (cutaneous) symptoms.
Acute intermittent porphyria is due to a deficiency of the enzyme porphobilinogen deaminase (also known as hydroxymethylbilane synthase) that leads to accumulation of the heme precursors delta-aminolevulinic acid and porphobilinogen initially in the liver.
The disorder is inherited due to a single abnormal gene from one parent. The normal gene from the other parent keeps the deficient enzyme at half-normal levels, which is sufficient to produce normal amounts of heme.
Most people with a deficiency of porphobilinogen deaminase never develop symptoms. In some people, however, certain factors can precipitate symptoms, causing an attack. Factors that can cause an acute porphyria attack include
Usually a combination of factors is involved in causing an attack. Sometimes the factors that cause an attack cannot be identified.
Attacks are more common in women than in men and occur only very rarely before puberty. Very rarely, the disorder is inherited from both parents (and therefore two abnormal genes are present). Symptoms may then appear in childhood and include developmental abnormalities.
Some Drugs That May Cause an Attack of Acute Intermittent Porphyria*
Many people never experience symptoms of acute intermittent porphyria. Symptoms occur as attacks usually lasting a few days but occasionally longer. Such attacks usually first appear after puberty. In some women, attacks develop during the second half of the menstrual cycle, likely triggered by the elevation of progesterone levels that occurs then.
Abdominal pain is the most common symptom. The pain can be so severe that doctors may mistakenly think that abdominal surgery is needed. Other digestive symptoms include nausea, vomiting, severe constipation, or diarrhea (rarely).
Mental symptoms, such as irritability, restlessness, insomnia, agitation, tiredness, and depression, are common.
Nervous system symptoms are numerous. Nerves that control muscles can be affected, leading to weakness, usually beginning in the shoulders and arms. The weakness can progress to virtually all the muscles, including those involved in breathing. Tremors and seizures may develop.
Urinary symptoms may occur. The bladder may be affected, making urination difficult and sometimes resulting in an overly full bladder. Urine may be red or reddish brown.
Other common symptoms include
Most of these symptoms, including the digestive ones, result from effects on the nervous system.
Irregular heart rhythm is a dangerous complication during an attack.
Recovery from symptoms may occur within a few days, although complete recovery from severe muscle weakness may take several months or years. Attacks are rarely fatal. However, in a few people, attacks are disabling.
Long-term complications of acute porphyria may include persistent muscle weakness, high blood pressure, kidney failure, cirrhosis, and liver tumors.
The severe gastrointestinal and neurologic symptoms of acute intermittent porphyria resemble symptoms of many more common disorders. Laboratory tests done on samples of urine taken during an attack show increased levels of two heme precursors (delta-aminolevulinic acid and porphobilinogen). Levels of these precursors are very high during attacks and remain high in people who have repeated attacks.
The precursors can form porphyrins, which are reddish. These porphyrins turn the urine red to red-brown. The color is especially evident after the urine specimen is exposed to light and air.
Relatives without symptoms can be identified as carriers of the disorder by measuring porphobilinogen deaminase in red blood cells or, with greatest certainty, by DNA testing. Diagnosis before birth is also possible but usually is not needed because most affected people never get symptoms.
Attacks of acute intermittent porphyria can be prevented by
People who have attacks at predictable times, such as women whose attacks are related to the menstrual cycle, can be given heme by vein to prevent attacks. Premenstrual attacks in women can be prevented with one of the gonadotropin-releasing hormone agonists used to treat endometriosis, although this treatment should only be directed by doctors who are experts in treating porphyria.
Treatment of the acute attack is identical for all the acute porphyrias.
People who have attacks of acute intermittent porphyria are often hospitalized for treatment of severe symptoms.
People with severe attacks are treated with heme given by vein. Blood and urine levels of delta-aminolevulinic acid and porphobilinogen are promptly lowered and symptoms subside, usually within several days. If treatment is delayed, recovery takes longer, and some nerve damage may be permanent.
Glucose given by mouth (or by vein if people are vomiting) can also be beneficial, particularly in people whose attacks are brought on by a low-calorie, low-carbohydrate diet, but these measures are less effective than heme.
Pain can be controlled with drugs (such as opioids).
Nausea, vomiting, anxiety, and restlessness are treated with a phenothiazine-type drug for a short time. Ondansetron may also be given for nausea.
Insomnia may be treated with chloral hydrate or low doses of a benzodiazepine but not a barbiturate. An overly full bladder may be treated by draining the urine with a catheter.
Doctors ensure that people do not take any of the drugs known to precipitate an attack, and—if possible—address other factors that may have contributed to the attack. Treatment of seizures is problematic, because almost any anticonvulsant would worsen an attack. Levetiracetam appears to be safe to use. Beta-blockers may be used to treat rapid heart rate and high blood pressure.
Liver transplantation will cure the disorder. Doctors consider transplantation for people with poor quality of life and risk of permanent kidney or nervous system damage because of severe recurrent attacks. Some people may also need kidney transplantation.