Characterizing breach rhythm in EEG: Insights into its variability and clinical impact.

OBJECTIVE

Breach rhythm (BR) is an EEG phenomenon typically associated with skull defects. While its continuous form is well recognized, the significance of intermittent BR has not been systematically studied.

METHODS

This cross-sectional, multicenter observational study included 90 patients with BR on routine EEGs. Patients were categorized based on BR continuity (continuous BR, CBR vs. intermittent BR, IBR). Structural imaging parameters, including residual lesion volume (RLV) and skull defect measurements, were also analyzed.

RESULTS

Of 90 patients, 55 (61.1%) had CBR and 35 (38.9%) had IBR. There were no significant differences in demographic or seizure characteristics between groups. Residual lesion volumes were significantly larger in the CBR group, while skull defect size and surface area did not differ between groups. Interictal epileptiform discharges within BR regions were common in both groups (52.7% vs. 65.7%, p= 0.224). However, non-epileptiform interictal abnormalities outside BR regions were significantly more frequent in the IBR group (37.1% vs. 5.5%, p< 0.01). Right-sided BR was more often (70.2%) continuous than left-sided BR (48.8%) (p= 0.040).

CONCLUSIONS

Breach rhythm on EEG can present as a continuous or intermittent pattern. Continuous BR appears associated with greater residual lesion burden and focal neurological findings, whereas intermittent BR is linked to smaller residual lesions but more widespread cortical abnormalities beyond the breach region. These findings suggest that BR reflects not only skull defects but also the functional state of underlying cortex.

SIGNIFICANCE: This study is the first to systematically differentiate intermittent from continuous BR, demonstrating that intermittent BR is common and BR may serve as a marker of distributed or dynamic cortical dysfunction in addition to structural cranial abnormalities.