5. Acute Porphyria
Definition
Porphyria, in general, is a broad disease category that encompasses eight distinct, related disorders. The acute variants may be characterized by demonstration of abdominal pain, neuropathy, autonomic instability, and/or psychosis.
Incidence
The estimated incidence of acute porphyria is variable. Across Europe, the overall incidence is about 1:20,000; in northern Sweden, the incidence is about 1:10,000. Internationally, the estimated incidence is about 5:100,000.
Etiology
Each acute porphyria variant is produced by an inherited deficiency of a specific enzyme required for progression through the pathway to completion of heme production.
Signs and Symptoms
• Abdominal pain
• Agitation
• Anxiety
• Aphasia
• Apraxia
• Bladder dysfunction
• Confusion
• Cortical blindness
• Depression
• Dysesthesias
• Dysuria
• Encephalopathy
• Fever
• Guillain-Barré–like syndrome
• Hallucinations
• Hyperhidrosis
• Hypersecretion of catecholamines
• Hypertension
• Insomnia
• Mild-to-severe paresthesias
• Motor nerve palsies (especially cranial nerves VII and X)
• Nausea
• Numbness
• Optic nerve dysfunction (may deteriorate to blindness)
• Paranoia
• Partial ileus
• Rhabdomyolysis
• Seizures
• Tachycardia
• Tremor
• Urine color changes to red or becomes very dark when exposed to light
• Vomiting
Medical Management
For the patient with an acute porphyria variant, the first-line intervention during an acute episode begins with removal of any initiating medication or agent. The patient should receive intravenous hydration with carbohydrate-containing solutions, such as dextrose 10%. Abdominal pain should be controlled with opioid analgesics; nausea and vomiting that occurs should be treated with phenothiazine agents. Should these interventions fail to provide symptomatic relief, an intravenous infusion of heme is generally initiated for a period ranging from 3 to 14 days.
If the patient with an acute porphyria experiences seizures, the first intervention should be to determine serum electrolyte concentrations and serum osmolarity as quickly as possible. Acute porphyria patients are prone to develop hyponatremia as well as syndrome of inappropriate antidiuretic hormone (SIADH), either of which can result in seizure. Immediate control of seizures can be achieved with intravenous diazepam or magnesium sulfate to allow time for laboratory tests to be completed and the results transmitted. Correction of electrolyte imbalances may reverse the seizures. If epilepsy is the concurrent cause, seizure control can be safely attained with gabapentin. Rectal administration of diazepam may be necessary to achieve a useful degree of seizure control.
Autonomic instability that may accompany an acute episode can be successfully managed using β-blocking agents. Acute hypertension should be treated quickly to prevent development of undesirable sequelae, such as stroke. Phenothiazine medications, effective against episodes of nausea and vomiting, also help control any psychiatric symptoms that may arise.
Complications
• Adrenergic crisis