Diagnostic Approach to Episodic Encephalopathy with Normal Ammonia Levels

Key Diagnostic Principles

• A normal blood ammonia level has high negative predictive value for hepatic encephalopathy, indicating the patient lacks sufficient hepatic failure and/or portosystemic shunting to justify a working diagnosis of HE, according to the European Association for the Study of the Liver 1, 2, 4
• Normal ammonia levels in a patient with episodic encephalopathy and liver disease essentially rule out hepatic encephalopathy as the primary diagnosis and mandate an immediate search for alternative causes of delirium, as recommended by the American Association for the Study of Liver Diseases 1, 2, 3

Alternative Causes to Investigate When Ammonia is Normal

• Electrolyte disturbances, such as hyponatremia, hypercalcemia, and other imbalances, commonly cause episodic confusion, as noted by the National Institute of Diabetes and Digestive and Kidney Diseases 5
• Renal dysfunction, including uremic encephalopathy, can mimic HE with similar EEG changes, according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 5
• Thiamine deficiency, particularly in malnourished patients or those with alcohol use disorder, can cause Wernicke's encephalopathy, as warned by the World Health Organization 5
• Hypoglycemia or hyperglycemia can cause diabetic encephalopathy, as reported by the American Diabetes Association 5
• Septic encephalopathy, systemic infection without CNS involvement, can cause delirium, as stated by the Infectious Diseases Society of America 5
• CNS infections, such as meningitis or encephalitis, require lumbar puncture evaluation, according to the Centers for Disease Control and Prevention 6
• Intracranial hemorrhage, especially in patients with alcohol-related cirrhosis, can cause episodic confusion, as noted by the American Heart Association 1, 2
• Subdural hematoma, common in elderly or those with falls, can cause episodic confusion, as reported by the American Academy of Neurology 1
• Stroke or transient ischemic attacks can present with episodic confusion, as stated by the American Stroke Association 6
• Mild cognitive impairment (MCI) and dementia can have significant overlap with covert HE symptoms, particularly in patients >60 years old, as noted by the Alzheimer's Association 6

Recommended Diagnostic Workup

• Comprehensive metabolic panel, including sodium, calcium, glucose, and renal function, is essential for immediate laboratory assessment, as recommended by the National Institute of Diabetes and Digestive and Kidney Diseases 5
• Medication review to identify potentially offending agents is crucial, as stated by the American Medical Association 5
• Thiamine level should be checked, especially if malnutrition or alcohol use disorder is present, as recommended by the World Health Organization 5
• CT scan or MRI should be performed in cases of diagnostic doubt or non-response to treatment, with a strong recommendation and 96% consensus, to exclude intracranial hemorrhage, structural lesions, and brain atrophy, as noted by the American College of Radiology 1, 2, 6
• EEG can help differentiate causes and would not be altered by diabetes or alcohol disorders but may show changes similar to HE in renal dysfunction, hyponatremia, or septic encephalopathy, as reported by the American Academy of Neurology 5
• Lumbar puncture is necessary if CNS infection is suspected, as stated by the Centers for Disease Control and Prevention 6

Clinical Pitfalls to Avoid

• Do not assume HE based on liver disease alone, as the presence of cirrhosis does not mean all encephalopathy is hepatic in origin, as warned by the American Association for the Study of Liver Diseases 6, 8
• Recognize episodic patterns, as the fluctuating nature of covert HE differs from the more persistent cognitive impairment of MCI, as noted by the Alzheimer's Association 6
• Consider multiple concurrent causes, as patients with cirrhosis, especially elderly, frequently have comorbidities that overlap with HE symptoms, as reported by the European Association for the Study of the Liver 1, 6
• Response to HE therapy as diagnostic tool, if symptoms do not improve with lactulose/rifaximin, this further supports an alternative diagnosis, as stated by the American Association for the Study of Liver Diseases 6