Abstracts

Rationale: Isodicentric chromosome [idic(15)] is a rare chromosomal abnormality that occurs due to inverted duplication of chromosome 15q. It is associated with many clinical findings including early central hypotonia, developmental delay, cognitive dysfunction, autistic behavior and epilepsy. We report a case of Idic(15) and characterstic Electroencephalogram [EEG] findings which can allow for early diagnosis. Methods: Retrospective chart review and literature search utilizing Pubmed and Medline. Results: We report a case of a 17 year old girl with Idic(15) who was referred for her refractory epilepsy, global developmental delay and autistic behavior. She was born at term by normal delivery after an uneventful pregnancy. There was no significant past and family medical history. Initial metabolic evaluation was normal. A brain magnetic resonance imaging showed prominent ventricles and sulci with periventricular leukomalacia. A Positron Emission Tomography of brain was normal. Genetic analysis showed inverted duplication of Chromosome 15q. She had recurrent seizures from the age of 7 years and of varying types including asymmetric tonic, atonic, focal, and generalized tonic-clonic that were refractory to Valproic acid, Lamotrigine and Rufinamide. Multiple routine Electroencephalogram recordings were consistent with symptomatic generalized epilepsy with interictal findings of slow background activity with multifocal sharp waves of variable hemispheric predominance and paucity of sleep spindles and K-complexes in sleep. In addition, excessive diffuse 13-30 Hz beta activity was noted. Long-term video monitoring showed similar interictal characteristics with excessive beta activity. Clinical seizures correlated with ictal EEG findings, consisting of 9-14 Hz bilateral frontally-dominant high amplitude sharp wave discharges lasting 5-10 seconds, at times followed by diffuse 1.5-3 Hz delta slowing. Conclusions: 63% of the patients with Idic(15) have seizures and 81% have multiple seizure types. Diagnosis is typically dependent on Fluorescent in situ hybridization (FISH) or array comparative genomic hybridization (array-CGH). The Electroencephalogram in this patient showed features of generalized epilepsy, however a specific pattern of interictal and ictal abnormalities can distinguish this syndrome from other symptomatic epilepsies. In our patient we identified excessive 13-30 Hz beta activity interictally despite the lack of common causative agents. The excessive diffuse beta activity and ictal 9 -14 Hz frontally-dominant high amplitude sharp wave discharges seen on this patient's EEG are pathognomonic and consistent with similar EEG findings that have been reported in earlier published studies (Urraca et al. 2014 and Thibert et al, MGH dup15q center). Awareness of such EEG characteristics may aid in timely recognition and diagnosis of Idic(15) syndrome, and also lead to more appropriate early treatment of epilepsy in this patient population.