Prolonged psychiatric symptoms revealed as nonconvulsive status epilepticus in ring chromosome 20 syndrome.

Ring chromosome 20 (r[20]) syndrome is a rare epilepsy-associated chromosomal disorder often accompanied by intellectual disability and psychiatric symptoms. It lacks distinctive physical features and typically exhibits normal brain imaging; therefore, its diagnosis is frequently delayed, especially when clinicians are unfamiliar with it. Nonconvulsive status epilepticus (NCSE), a hallmark of this syndrome, can be overlooked even by epilepsy specialists, who interpret it as a psychiatric symptom, particularly in patients with limited expressive capacity. A 42-year-old woman with a long-standing history of drug-resistant epilepsy and behavioral symptoms was ultimately diagnosed with r(20) syndrome. She developed tonic seizures and fear episodes at age 6 and was diagnosed with epilepsy. After age 11, drug-resistant NCSE emerged and was not clearly identified as status epilepticus; it was considered to involve impaired awareness seizures and psychiatric symptoms. At age 41, perampanel (PER) was initiated, triggering aggressive behavior and new backward-falling episodes, further complicating her clinical presentation. Video electroencephalogram (EEG) confirmed NCSE, and chromosomal analysis identified r(20). After PER discontinuation, aggression and backward-falling episodes resolved. Lacosamide was introduced, reducing the frequency of NCSE from several daily episodes to 2-3 per week. This case underscores the diagnostic challenges of r(20) syndrome and the risk of misdiagnosing NCSE as a psychiatric illness. Additionally, PER may exacerbate psychiatric symptoms in r(20) cases with intellectual disability. Precise seizure classification and confirmation by ictal EEG, along with integrated neuropsychiatric care, are essential for accurate diagnosis and effective management.