What are the initial diagnostic procedures for patients presenting with seizures?

Initial Diagnostic Procedures for Seizure Patients

In the emergency setting, obtain a non-contrast head CT immediately to identify life-threatening structural pathology, while MRI brain without contrast is the definitive imaging study for non-emergent evaluation and should be arranged for all seizure patients. 1, 2

Immediate Laboratory Testing

Essential metabolic workup:

• Serum glucose and sodium levels must be checked immediately, as these are the only laboratory abnormalities that consistently alter acute management and are the most frequent metabolic causes of seizures 2, 3
• Pregnancy test for all patients of childbearing age who have reached menarche 2
• Additional labs (CBC, comprehensive metabolic panel, calcium, magnesium) should only be obtained when specific clinical findings suggest them, such as vomiting, diarrhea, dehydration, known cancer, or renal failure 2

Neuroimaging Algorithm

Emergency Setting (Perform CT Head Without Contrast When):

• New focal neurological deficits present 2
• Persistent altered mental status or failure to return to baseline 2
• Fever with concern for CNS infection 2
• Recent head trauma 2
• Persistent headache 2
• History of malignancy or immunocompromised state 2
• Patient on anticoagulation 2
• Age >40 years or focal/partial seizure onset 2

CT rapidly identifies intracranial hemorrhage, stroke, vascular malformation, hydrocephalus, and tumors requiring urgent neurosurgical intervention, but detects only 30% of epileptogenic lesions compared to MRI's 55-70% detection rate 1

Non-Emergent Setting (Arrange Outpatient MRI Brain):

• MRI without contrast is the imaging study of choice for all patients with new-onset seizures when not in an emergency situation 1, 2, 3
• Use dedicated epilepsy protocol including: coronal T1-weighted imaging perpendicular to hippocampus (3mm slices), high-resolution 3D T1-weighted gradient echo (1mm isotropic voxels), coronal T2, and coronal/axial FLAIR sequences 1, 4
• MRI detects 29% of abnormalities missed by initial CT in children with new-onset seizures, and 47% of abnormalities in status epilepticus patients 1

Exceptions where MRI may not be necessary:

• Neurologically normal patients with typical primary generalized epilepsy (juvenile myoclonic epilepsy, childhood absence) with characteristic EEG features and adequate response to antiepileptic drugs 1
• Simple febrile seizures in children 6 months-5 years 2

Electroencephalography (EEG)

• EEG should be obtained as part of the neurodiagnostic evaluation for all patients with apparent first unprovoked seizure 2
• Abnormal EEG findings predict increased risk of seizure recurrence and help guide treatment decisions 2
• EEG assists in seizure classification, identification of epilepsy syndrome, and localization of seizure focus 5, 6
• The EEG refines probability but neither proves nor excludes seizure diagnosis—clinical history remains primary 5

Lumbar Puncture Indications

Perform lumbar puncture (after head CT) when:

• Concern for meningitis or encephalitis exists (fever with meningeal signs, persistent altered mental status without alternative explanation) 2
• Patient is immunocompromised 2
• Autoimmune encephalitis suspected (requires CSF analysis, brain MRI with contrast, and serum neural antibody panel) 2

Lumbar puncture is NOT routinely indicated for uncomplicated first-time seizures 2

Risk Stratification for Imaging Priority

High-risk features requiring urgent imaging:

• Focal findings on neurological examination 1, 2
• Persistent headache 1, 2
• Recent head trauma 1, 2
• Abnormalities on EEG 1, 2
• Post-ictal focal deficit not quickly resolving 2
• Has not returned to baseline within several hours 2

Low-risk patients (young, returned to baseline, normal neurologic exam, reliable follow-up) can have deferred outpatient MRI, though 22% will still have significant epileptogenic lesions 2, 3

Pediatric-Specific Considerations

• For focal seizures in children, MRI demonstrates abnormalities in 55% versus only 18% with CT 1
• Approximately 4% of children with first-time afebrile focal seizures have urgent intracranial pathology (infarction, hemorrhage, thrombosis) 1, 4
• For neurologically normal children with primary generalized seizures, imaging has very low yield (only 2% abnormal findings) and is typically not indicated 1
• Consider toxicology screening if drug exposure or substance abuse suspected 2

Common Pitfalls to Avoid

• Failing to check glucose and sodium immediately—these are correctable causes requiring urgent intervention 2
• Missing structural lesions by not performing appropriate neuroimaging—28% of abnormalities are missed on initial CT 1
• Assuming alcohol withdrawal as cause without excluding other symptomatic causes, especially in first-time seizures 2
• Approximately 28-48% of suspected first seizures have alternative diagnoses (syncope, nonepileptic seizures, panic attacks)—careful history is essential 2

Advanced Imaging for Refractory Cases

When MRI is normal but seizures persist and surgery is considered:

• FDG-PET/CT shows 87-90% sensitivity for temporal lobe epilepsy and 38-55% for extra-temporal epilepsy 4
• Statistical ictal SPECT co-registered to MRI identifies hyperperfusion focus in 84% of patients 1, 4
• These functional imaging modalities are complementary to structural MRI in presurgical planning 1