Occipital irregular delta activity in focal epilepsy

Nonspecific occipital irregular delta activity (OID) is a common finding in focal epilepsy (FE). However, the significance of OID and its relationship to the underlying etiology of FE remain largely unstudied. This study aimed to investigate the relationship between OID and the etiology of FE, as well as the relationship between OID and the clinical characteristics of patients with FE.

We retrospectively reviewed the clinical data and electroencephalography (EEG) reports of 963 patients with FE (full study sample) and 116 healthy controls to assess the prevalence of OID in both groups. Statistical associations were computed between OID and the following clinical variables: age at onset of the illness, sex, and family history of seizures. After excluding patients with no definite etiological diagnosis, the remaining patients comprised the reduced study sample (n = 772). In this reduced sample, we analyzed the relationship between OID and etiology (symptomatic vs. idiopathic). Statistical analysis was performed using multiple chi-square tests with False Discovery Rate correction.

The prevalence of OID was significantly higher in the full study sample (7.8%) than in the controls (.9%; p = .0059). OID showed a positive statistical association with idiopathic etiology and a negative association with symptomatic etiology (p = .0001). OID was positively associated with younger age at onset (1-25 years) and a positive family history of seizures, and negatively associated with adult age (26-78 years; p = .0004) and a negative family history of seizures (p = .0205).

The relationship between OID and idiopathic FE was statistically significant. Several lines of evidence suggest a neurobiological relationship between the presence of OID, age-dependent epilepsies, and delayed brain maturation, particularly in younger individuals.

From the practical perspective, OID could serve as a potential age-dependent EEG marker of idiopathic FE. In most cases, the presence of OID contradicts a symptomatic etiology.