Intermittent rhythmic delta activity (IRDA) in a patient with band heterotopia

ILAE neuroimaging task force highlight: Subcortical laminar heterotopia

The ILAE Neuroimaging Task Force publishes educational case reports that highlight basic aspects of neuroimaging in epilepsy consistent with the ILAE's educational mission. Subcortical laminar heterotopia, also known as subcortical band heterotopia (SBH) or "double cortex," is an intriguing and rare congenital malformation of cortical development. SBH lesions are part of a continuum best designated as agyria-pachygyria-band-spectrum. The malformation is associated with epilepsy that is often refractory, as well as variable degrees of developmental delay. Moreover, in an increasing proportion of cases, a distinct molecular-genetic background can be found. Diagnosing SBH can be a major challenge for many reasons, including more subtle lesions, and "non-classic" or unusual MRI-appearances. By presenting an illustrative case, we address the challenges and needs of diagnosing and treating SBH patients in epilepsy, especially the value of high-resolution imaging and specialized MRI-protocols.

Generalized and Lateralized Rhythmic Patterns

The relationship between generalized and lateralized rhythmic delta activity (RDA) and seizures is more ambiguous than the relationship between periodic discharges and seizures. Although frontally predominant generalized RDA is not associated with seizures, occipitally predominant RDA may be associated with the absence of seizures. Lateralized RDA seems to be more strongly associated with the presence of seizure activity. Appropriate recognition of generalized RDA and lateralized rhythmic delta activity may be confounded by benign etiologies of RDA, such as phi rhythm, slow alpha variant, subclinical rhythmic electrographic discharges of adults, or hyperventilation-induced high-amplitude rhythmic slowing. Angelman syndrome and NMDA-receptor antibody encephalitis can also produce morphologically distinct patterns of RDA.

Ictal EEG patterns in band heterotopia

Band heterotopia (BH) or "double cortex" syndrome is a neuronal migration disorder resulting in a diffuse band of subcortical grey matter and variable abnormality of the overlying cortex. Patients with BH have a spectrum of psychomotor delay and seizures. Associated epileptic syndromes and interictal EEG findings have been described, but ictal EEG patterns are lacking.

METHODS

We describe the clinical, interictal, and ictal EEG findings in two girls with BH and intractable seizures.

RESULTS

Ictal EEG patterns correlated well with clinical seizure types, and did not have features unique to BH. Similarly, seizure behaviors and interictal EEG findings were typical of those seen in symptomatic generalized epilepsies.

CONCLUSIONS

Despite evidence implicating the ectopic grey matter in seizure discharges, we conclude that seizure semiology and associated ictal EEG patterns in BH are no different from those seen in other causes of symptomatic generalized epilepsies.