Focal seizure symptoms in idiopathic generalized epilepsies

Seneviratne U, Woo JJ, Boston RC, Cook M, D'Souza W. Focal seizure symptoms in
idiopathic generalized epilepsies. Neurology. 2015 Aug 18;85(7):589-95.

Abstract

OBJECTIVE:

We sought to study the frequency and prognostic value of focal seizure symptoms (FSS) in idiopathic generalized epilepsies (IGE) using a validated tool: Epilepsy Diagnostic Interview Questionnaire and Partial Seizure Symptom Definitions.

METHODS:

Participants with IGE were recruited from epilepsy clinics at 2 tertiary hospitals. The diagnosis was validated and classified into syndromes according to the International League Against Epilepsy criteria by 2 epileptologists independently with discordance resolved by consensus. The Epilepsy Diagnostic Interview Questionnaire utilizes both open- and closed-ended questions to elicit FSS in association with generalized tonic-clonic seizures, myoclonus, and absences. The elicited FSS were classified according to the Partial Seizure Symptom Definitions. Regression analysis was conducted to examine the relationship between the duration of seizure freedom and FSS.

RESULTS:

A total of 135 patients were studied, of whom 70 (51.9%) reported FSS. Those symptoms occurred in association with generalized tonic-clonic seizures (53.1%) as well as myoclonus and absences (58%). FSS were reported with similar frequency in juvenile absence epilepsy (62.5%) and juvenile myoclonic epilepsy (60%), and with a lesser frequency in generalized epilepsy with tonic-clonic seizures only (39.5%) and childhood absence epilepsy (33.3%). A strong relationship between FSS and duration of seizure freedom was found (regression coefficient -0.665, p = 0.037).

CONCLUSIONS:

FSS are frequently reported by patients with IGE. A shorter duration of seizure freedom is associated with FSS. Recognition of the presence of FSS in IGE is important to avoid misdiagnosis and delayed diagnosis as well as to choose appropriate antiepileptic drug therapy.

From the paper:

The most interesting and novel finding in our study is the association between FSS and duration of seizure freedom. A shorter duration of seizure freedom was significantly associated with FSS. This relationship was unaffected by confounders such as number of AEDs, age of seizure onset, age at interview, duration of epilepsy, presence of GTCS, and presence of focal discharges in the EEG. We acknowledge that 95% confidence interval includes zero when adjusted for some confounders such as number of AEDs. However, we believe it is attributable to the relatively small sample size, and the association between the duration of seizure freedom and FSS is still clinically relevant. Overall, our study raises the possibility that the presence of FSS may be an important prognostic factor associated with the duration of seizure freedom. Previous studies have reported conflicting results on the presence of focal EEG abnormalities as a predictor of prognosis. To our knowledge, the prognostic significance of FSS in IGE has not been previously published. However, an alternative explanation is recall bias, whereby those with a shorter duration of seizure freedom and more frequent seizures may be more likely to remember their FSS. Patients with shorter durations of seizure freedom have had more recent seizures, hence, are more likely to be able to reinforce their perceptions and recall subtle FSS...

Our study demonstrates that FSS are often reported by patients with IGE in association with both major and minor seizures. The duration of seizure freedom is associated with FSS. Our findings have implications for clinical practice. First, we emphasize that clinicians need to be aware of FSS in IGE to avoid misdiagnosis and delayed diagnosis as well as to choose appropriate AED treatment. Second, FSS may lead to inappropriate investigations for focal epilepsy including evaluation for epilepsy surgery. Third, the presence of FSS should alert the clinician as a potential marker of reduced likelihood of prolonged seizure freedom. Further studies are needed to confirm these findings, preferably in incident cases with prospective follow-up, and to examine the underlying pathophysiologic and network mechanisms of focal abnormalities in IGE. A greater understanding of these network mechanisms may assist in long-term management of IGE.