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ACUTE INTERMITTENT PORPHYRIA

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ESSENTIALS OF DIAGNOSIS

  • Unexplained abdominal crisis, generally in young women.

  • Acute peripheral or central nervous system dysfunction; recurrent psychiatric illnesses.

  • Hyponatremia.

  • Porphobilinogen in the urine during an attack.

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General Considerations

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Though there are several different types of porphyrias, the one with the most serious consequences and the one that usually presents in adulthood is acute intermittent porphyria (AIP), which is inherited as an autosomal dominant, though it remains clinically silent in most patients who carry a mutation in HMBS. Clinical illness usually develops in women. Symptoms begin in the teens or 20s, but onset can begin after menopause in rare cases. The disorder is caused by partial deficiency of hydroxymethylbilane synthase activity, leading to increased excretion of aminolevulinic acid and porphobilinogen in the urine. The diagnosis may be elusive if not specifically considered. The characteristic abdominal pain may be due to abnormalities in autonomic innervation in the gut. In contrast to other forms of porphyria, cutaneous photosensitivity is absent in AIP. Attacks are precipitated by numerous factors, including drugs and intercurrent infections. Harmful and relatively safe drugs for use in treatment are listed in Table 40–1. Hyponatremia may be seen, due in part to inappropriate release of antidiuretic hormone, although gastrointestinal loss of sodium in some patients may be a contributing factor.

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Table Graphic Jump Location
Table 40–1.Some of the “unsafe” and “probably safe” drugs used in the treatment of acute porphyrias.
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Clinical Findings

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A. Symptoms and Signs
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Patients show intermittent abdominal pain of varying severity, and in some instances it may so simulate acute abdomen as to lead to exploratory laparotomy. Because the origin of the abdominal pain is neurologic, there is an absence of fever and leukocytosis. Complete recovery between attacks is usual. Any part of the nervous system may be involved, with evidence for autonomic and peripheral neuropathy. Peripheral neuropathy may be symmetric or asymmetric and mild or profound; in the latter instance, it can even lead to quadriplegia with respiratory paralysis. Other central nervous system manifestations include seizures, altered consciousness, psychosis, and abnormalities of the basal ganglia. Hyponatremia may further cause or exacerbate central nervous system manifestations.

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B. Laboratory Findings
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Often there is profound hyponatremia. The diagnosis can be ...

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