Do individuals with trisomy 18 experience seizures?

Seizures in Trisomy 18

Yes, individuals with trisomy 18 commonly experience seizures, with approximately 28% developing them at some point in their lifetime, and these seizures can be effectively managed with broad-spectrum anti-seizure medications in many cases. 1

Seizure Prevalence and Types

• Seizures occur in roughly one-quarter to one-third of individuals with trisomy 18, representing a significant neurological comorbidity in this population 1
• Multiple seizure types can manifest, including generalized tonic-clonic, focal (with or without impaired awareness), mixed seizures, and infantile spasms 1, 2
• The presence of structural brain malformations significantly impacts seizure characteristics—patients with brain abnormalities develop seizures much earlier (median age 2 months) compared to those with normal brain imaging (median age 21 months) 2

Clinical Presentation and Risk Factors

• Individuals who previously experienced infantile spasms or central apnea have a higher likelihood of developing focal and generalized seizures 1
• Patients with structural brain malformations (including commissural anomalies, cerebellar malformations, cortical abnormalities, and cortical atrophy) present with more severe seizure semiology, multiple seizure types, and multifocal EEG abnormalities 2
• Seizures may progress over time—one documented case showed initially well-controlled seizures at age 9 that eventually progressed to refractory generalized and myoclonic epilepsy requiring vagus nerve stimulator placement 3

Diagnostic Approach

Electroencephalogram (EEG) testing should be considered as part of standard screening in individuals with trisomy 18 to enable early diagnosis and treatment of seizures 1

• Brain imaging (CT or MRI) is essential to evaluate for structural abnormalities that predict seizure severity and treatment response 2
• Patients with normal brain imaging typically show non-specific EEG patterns and single seizure types, while those with structural abnormalities demonstrate multifocal EEG abnormalities 2

Treatment Strategy

Broad-spectrum anti-seizure medications are effective for managing seizures in many individuals with trisomy 18 1

• Patients without structural brain malformations respond well to monotherapy with good outcomes and can be successfully controlled with single anti-seizure medications 2
• Those with structural brain abnormalities frequently require polytherapy (80% of cases) and have poorer outcomes, with 90% developing drug-resistant epilepsy 2
• Standard anticonvulsant medications appear effective for non-hypocalcemic seizures in these patients 4

Important Caveats

• Hypocalcemia can trigger or exacerbate seizures in trisomy 18 patients, particularly given the multiple metabolic vulnerabilities in this population 4
• If seizures persist despite anti-seizure medication, verify adequate calcium correction (ionized calcium >0.9 mmol/L) and check magnesium levels, as hypomagnesemia can prevent calcium normalization 4
• Avoid enzyme-inducing antiepileptic drugs when possible to prevent recurrent hypocalcemia 4
• Seizure prevalence may be underestimated, as complex partial seizures can present as confusion or memory loss rather than obvious convulsions 4