What is the proper diagnosis for seizures due to metabolic causes?

Proper Diagnosis for Seizures Due to Metabolic Causes

The proper diagnosis for seizures due to metabolic causes requires testing for serum glucose and sodium levels as the primary laboratory evaluation, as these are the most common metabolic abnormalities associated with seizures. 1

Initial Diagnostic Approach

• Metabolic seizures are classified as "reactive seizures" - a response of the cerebral cortex to extracranial disease rather than primary epilepsy 2
• Laboratory testing should begin with core tests, even though the yield is low in patients who have returned to baseline neurological status 1
• A pregnancy test is mandatory for all women of childbearing age, as pregnancy affects testing, disposition, and antiepileptic drug therapy 1

Essential Laboratory Tests for Metabolic Causes

• Core laboratory tests for all patients with suspected metabolic seizures:

  • Serum glucose (hypoglycemia/hyperglycemia) 3, 1
  • Serum sodium (hyponatremia) 3, 1
  • Pregnancy test for women of childbearing age 1

• Additional tests based on clinical presentation:

  • Calcium, magnesium, and phosphate levels for patients with:
    • Known renal insufficiency 1
    • Malnutrition 1
    • Patients taking diuretics 1
    • Suspected alcohol-related seizures (especially magnesium) 1, 4

Diagnostic Considerations for Specific Populations

• For patients with suspected alcohol-related seizures:

  • Alcohol withdrawal seizures should be a diagnosis of exclusion, especially in first-time seizures 3
  • Magnesium levels should be checked as hypomagnesemia is common in this population 1, 4

• For immunocompromised patients:

  • Complete metabolic panel 1
  • Head CT and lumbar puncture are recommended due to higher rates of CNS infections presenting with seizures 1
  • HIV testing should be considered, as HIV-seropositive patients with hypomagnesemia or renal failure appear to be at increased risk for convulsive status epilepticus 4

Diagnostic Yield and Evidence Base

• Studies consistently show that laboratory testing has a low yield in patients with new-onset seizures who have returned to baseline neurological status 3, 1
• Most metabolic abnormalities are predictable by history and physical examination 3
• In one prospective study, only 1 unexpected case of hypoglycemia was discovered in 163 patients 3
• In another study, 2 cases of unpredicted hypoglycemia were found in 136 patients 3

Additional Diagnostic Considerations

• Drug of abuse screen should be considered in patients with first-time seizures, though evidence for routine use is limited 3, 1
• Postictal laboratory values like creatine kinase (CK), electrolytes, creatinine, liver and renal function tests should be measured at least once to help identify the etiology of seizures with unknown causes 5
• Prolactin testing can help differentiate epileptic seizures from psychogenic non-epileptic seizures in adults and adolescents 5

Diagnostic Algorithm for Metabolic Seizures

1. For all seizure patients:

   • Check serum glucose and sodium 1
   • Pregnancy test for women of childbearing age 1

2. For patients with altered mental status, fever, or focal neurologic deficits:

   • Complete metabolic panel 1
   • Toxicology screen 1
   • Head CT 1
   • Consider lumbar puncture if appropriate 1

3. For patients with known medical disorders or taking diuretics:

   • Extended electrolyte panel including calcium, magnesium, and phosphate 1

4. For suspected alcohol-related seizures:

   • Complete metabolic panel with magnesium level 1, 4
   • Consider head CT 3

Remember that metabolic causes of seizures are potentially reversible if the underlying cause is detected and corrected, making accurate diagnosis crucial for proper treatment 2.