E80.21 Acute intermittent (hepatic) porphyria

Name of the Condition

• Acute Intermittent (Hepatic) Porphyria

Summary

Acute intermittent porphyria (AIP) is a genetic disorder of heme metabolism that causes acute neurological symptoms, often triggered by factors like medications, hormonal changes, or fasting. It results from a deficiency in the enzyme porphobilinogen deaminase, leading to the accumulation of porphyrin precursors. Symptoms typically involve abdominal pain, neuropsychiatric issues, and autonomic dysfunction, with skin involvement being rare. AIP is the most common acute porphyria and can present with severe, episodic attacks.

Causes

AIP is caused by mutations in the HMBS gene, which encodes the enzyme porphobilinogen deaminase. This genetic defect disrupts the heme biosynthesis pathway, leading to the buildup of toxic intermediates like aminolevulinic acid (ALA) and porphobilinogen (PBG). While the mutation is inherited, symptoms often appear only when triggered by external factors, such as certain drugs, alcohol, or hormonal fluctuations. The condition is autosomal dominant, meaning a single mutated copy of the gene can cause disease, though penetrance varies.

Risk Factors

• Genetic mutation in the HMBS gene (autosomal dominant inheritance).
• Exposure to triggering substances (e.g., certain antibiotics, anticonvulsants, or alcohol).
• Hormonal changes (e.g., menstrual cycles, pregnancy).
• Fasting or low-calorie diets.
• Stress or infections.
• Family history of AIP or unexplained acute neurological symptoms.

Symptoms

• Severe, cramping abdominal pain (often the first sign).
• Neuropsychiatric symptoms (e.g., anxiety, confusion, hallucinations, seizures).
• Autonomic dysfunction (e.g., tachycardia, hypertension, urinary retention).
• Peripheral neuropathy (e.g., weakness, pain, or numbness in limbs).
• Nausea, vomiting, or constipation.
• Rarely, skin photosensitivity (unlike other porphyrias).

Diagnosis

Diagnosis involves measuring elevated levels of ALA and PBG in urine during an acute attack. A 24-hour urine collection is standard, with levels typically rising 10–100 times normal. Genetic testing for HMBS mutations confirms the diagnosis, especially in asymptomatic family members. Other tests may rule out mimics (e.g., appendicitis or pancreatitis). Enzyme activity assays in red blood cells can also support the diagnosis but are less commonly used.

Treatment Options

• Acute attacks: Intravenous hemin therapy to reduce ALA/PBG production.
• Pain management: Opioids or non-opioid analgesics (avoid porphyrinogenic drugs).
• Supportive care: Hydration, electrolyte correction, and monitoring for complications.
• Long-term prevention: Avoiding triggers (e.g., certain medications, alcohol) and maintaining a balanced diet.
• Adjunct therapies: Beta-blockers for tachycardia or anticonvulsants for seizures (if needed).

Prognosis and Follow-Up

With prompt treatment, most acute attacks resolve within days to weeks. Long-term prognosis is good for those who avoid triggers, though recurrent attacks can occur. Complications like respiratory failure or chronic neuropathy may arise if untreated. Follow-up includes regular monitoring of symptoms, genetic counseling for family members, and education on trigger avoidance. Asymptomatic carriers may never develop symptoms.

Complications

• Respiratory failure (due to neuromuscular weakness).
• Chronic neuropathy (persistent pain or weakness).
• Hypertension or tachycardia (autonomic instability).
• Kidney or liver damage (rare, from repeated attacks).
• Psychiatric symptoms (e.g., depression or anxiety).

Lifestyle & Prevention

• Avoid known triggers: Certain medications, alcohol, and fasting.
• Maintain a regular diet: Avoid extreme calorie restriction.
• Manage stress: Techniques like meditation or therapy may help.
• Wear medical alert identification: For emergency situations.
• Educate family: About symptoms and genetic risks.

When to Seek Professional Help

Seek immediate care for severe abdominal pain, neurological symptoms (e.g., confusion, seizures), or signs of respiratory distress. Emergency treatment is critical to prevent life-threatening complications. Follow up with a specialist (e.g., gastroenterologist or geneticist) for ongoing management.

Tips for Medical Coders

Document the presence of acute neurological symptoms, trigger exposure, and diagnostic test results (e.g., elevated ALA/PBG) to support coding. Ensure the diagnosis is clearly differentiated from other porphyrias or mimics. Note that AIP is coded as E80.21 in ICD-10-CM, and specificity is required to avoid miscoding as a broader porphyria category.