Differential Diagnosis of Breakthrough Seizures
In a patient with established epilepsy experiencing breakthrough seizures, the most critical differential considerations are medication non-compliance, systemic infection with fever, psychogenic non-epileptic seizures (PNES), and co-occurring epileptic seizures with a different semiology.
Primary Causes to Evaluate
Medication Non-Compliance and Systemic Infection
- Non-compliance to anti-seizure medications accounts for 34.3% of breakthrough seizures, making it the second most common precipitating factor 1
- Systemic infection with fever is the leading trigger, occurring in 52.8% of breakthrough seizure cases 1
- Most parents and patients (69.5%) are unaware of these triggering factors, emphasizing the need for direct questioning 1
- Consider temporarily increasing anti-seizure medication dosages during febrile illnesses to prevent breakthrough events 1
Psychogenic Non-Epileptic Seizures (PNES)
- PNES must be distinguished from true epileptic seizures, as they occurred in 10% of patients enrolled in major status epilepticus trials 2
- Video-EEG monitoring is the gold standard for distinguishing PNES from epileptic seizures 3
- Historical features that suggest PNES include: prolonged duration (>2 minutes), gradual onset, side-to-side head movements, pelvic thrusting, eye closure during the event, and lack of post-ictal confusion 4
- Clinicians should evaluate all patients with seizure-like episodes for co-occurring psychiatric disorders 5
Key Clinical Features to Elicit
Witness and Patient History
- Obtain smartphone videos from patients and witnesses of the typical seizure-like episodes 5
- Patient and witness accounts alone are unreliable in a high percentage of cases, necessitating objective documentation 4
- Specifically ask about: fever or recent infections, medication adherence patterns, sleep deprivation, alcohol use, and new medications 1
Semiological Characteristics
- Focal seizures with impaired awareness may evolve into bilateral tonic-clonic seizures, representing progression rather than a new seizure type 2
- Immediate versus late post-traumatic seizures have different implications if there is a history of head trauma 2
- Pre-ictal pseudosleep (appearing to be asleep before the event) suggests PNES rather than epileptic seizures 6
Diagnostic Workup Algorithm
Initial Assessment
- Review medication levels and adherence history first, as this is readily modifiable 1
- Screen for acute systemic illness, particularly infections with fever 1
- Obtain detailed description of the breakthrough event's semiology compared to prior seizures 4
Neurophysiologic Testing
- Video-EEG monitoring should be obtained when feasible to capture all typical seizure-like episodes 5
- Routine interictal EEG has limited sensitivity but may show new epileptiform abnormalities suggesting disease progression 3
- In the study population, 77.8% had abnormal EEG findings 1
Neuroimaging Considerations
- MRI is pivotal when breakthrough seizures suggest new structural pathology (new focal features, change in seizure semiology) 3
- Structural lesions including tumors, infection, infarction, vascular malformations, and traumatic brain injury can cause seizure pattern changes 2
Common Pitfalls to Avoid
- Do not prescribe benzodiazepines or adjust anti-seizure medications for patients with PNES without co-occurring epilepsy 5
- Avoid assuming all breakthrough events are epileptic without considering the 10% baseline rate of PNES in epilepsy populations 2
- Do not rely solely on clinical criteria without EEG confirmation, as clinical assessment cannot distinguish postictal sedation from nonconvulsive status epilepticus 2
- Failing to assess for co-occurring epilepsy in patients with confirmed PNES, as both conditions can coexist 5
Additional Differential Considerations
Syncope and Other Paroxysmal Events
- Syncope, parasomnias, transient ischemic attacks, and migraine can mimic breakthrough seizures 3
- These are more relevant in new-onset events but should be considered if the semiology differs markedly from prior documented seizures 7