Clinical and Laboratory Manifestations
Acute intermittent porphyria is the most severe of the acute porphyrias. During an attack, patients display abdominal and neuro psychiatric or neurovisceral disturbances. Onset occurs in puberty; female patients exhibit a fourfold greater incidence of attacks than males. Attacks occur mainly in young adults and become less frequent after menopause. It is uncommon to see attacks in children. Crises may vary in duration from several days to months. They are most commonly followed by complete remission, although deaths are still reported, especially with AIP (see box on Precipitating Factors in Acute Porphyria). Late complications of AIP include renal impairment, hypertension, and hepatocellular carcinoma, and patients should be monitored for these complications.
Gastrointestinal symptoms occur in 95% of cases; most patients present with acute colicky central abdominal pain. Examination reveals tenderness but little rigidity, and patients may also experience limb pain or generalized muscular aches. Severe vomiting may occur, and constipation is usual. Hyponatremia occurs in severe attacks.
Motor neuropathy complicates two-thirds of porphyric attacks and may be the presenting feature. Motor involvement is most common, but paresthesias may also occur. Paralysis usually starts peripherally and then spreads proximally; however, in some patients, shoulder girdle involvement may be the first manifestation. The neuropathy may progress rapidly, resulting in respiratory insufficiency. Weakness, usually symmetric, involves proximal and distal limb muscles more often than those of the trunk. Upper limbs and proximal muscles are often affected. Involvement of the wrists, ankles, and small muscles of the hand may lead to a permanent deformity (Fig. 1), and trunk muscle weakness can lead to respiratory embarrassment. Death is usually caused by respiratory paralysis. Progressive weakening of the voice may suggest this; treatment requires tracheotomy and intermit tent positive pressure ventilation. Paresthesias, numbness, and objective evidence of sensory impairment may occur with loss of pinprick sensation, which is most marked around the shoulder and hip areas; generalized tonic-clonic seizures occasionally occur.
Fig1. BILATERAL WRISTDROP CAUSED BY PERIPHERAL NEUROPATHY IN A PATIENT WITH ACUTE INTERMITTENT PORPHYRIA.
Severe anxiety, depression, and frank psychosis are the main psychiatric manifestations of porphyric attacks. These psychiatric manifestations may result in a patient being misdiagnosed as suffering from a primary psychiatric disorder. Agitation, mania, depression, hallucinations, and schizophrenic-like behavior may occur. Psychiatric manifestations may persist between attacks. Quality of life is severely affected in those suffering from repeated attacks of acute porphyria.
The cardiovascular system is involved in approximately 70% of attacks. Sinus tachycardia (to 160 beats/min) and hypertension can occur; these elevations usually revert to normal after an attack. There is evidence that hypertension may occasionally be permanent, even in latent cases of AIP (see box on Differential Diagnosis of Acute Intermittent Porphyria).
