Trisomy 21-associated infantile epileptic spasms syndrome: optimizing first-line therapy

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Author: Joaquin A Pena MD

In Spanish: Síndrome de espasmos epilépticos infantiles asociado a trisomía 21: optimización del tratamiento de primera línea

Infantile epileptic spasms syndrome is a devastating form of infantile epilepsy and the most common epilepsy syndrome among children with trisomy 21. Although infantile epileptic spasms syndrome in this population has historically been considered to have a more favorable prognosis than in other symptomatic groups, recent multicenter data underscore the complexity of management and the high risk of neurodevelopmental sequelae, including ongoing epilepsy and autism spectrum disorder.

Although adrenocorticotropic hormone (ACTH), prednisolone, and vigabatrin are the "standard" therapies, many other antiseizure medications have been evaluated, typically in refractory cases. Interest in vigabatrin for trisomy 21 stemmed from early small-scale reports suggesting high response rates—some as high as 80%—and a perceived "favorable" outcome for this population. Furthermore, it offers ease of administration (oral vs. intramuscular) and fewer administrative hurdles, such as insurance approvals or specialty pharmacy delays often associated with ACTH.

As clinicians, our goal is to achieve rapid electroclinical remission to mitigate the effects of "epileptic encephalopathy," in which ictal activity itself contributes to cognitive and neurologic decline. This blog offers a structured overview of the current evidence, clinical controversies, and treatment recommendations for trisomy 21-associated infantile epileptic spasms syndrome.

Mechanism of action: why the trisomy 21 brain is different

The susceptibility to infantile epileptic spasms syndrome in trisomy 21 likely involves complex interactions among altered neuronal ion channels and neurotransmitter function.

Hormonal therapies (ACTH and prednisolone). Hormonal therapies are believed to act by lowering corticotropin-releasing hormone concentrations, a pro-epileptogenic neuropeptide.

Vigabatrin. Vigabatrin acts as an irreversible inhibitor of gamma-aminobutyric acid (GABA) transaminase, thereby increasing synaptic GABA concentrations.

Trisomy 21-specific pathogenesis. Research in the Ts65Dn mouse model has shown that overexpression of the GIRK2 protein (linked to GABAB receptors) is necessary for the development of the spasm phenotype. This suggests that trisomy 21 brains may have a specific predisposition to spasms that require targeted inhibition of specific pathways.

Clinical efficacy: hormonal therapy versus vigabatrin

Recent large-scale studies in North America and Europe have clarified the debate about the optimal first-line agent.

Remission rates. A multicenter North American analysis found that children with trisomy 21-associated infantile epileptic spasms syndrome were approximately twice as likely to achieve electroclinical remission with hormonal therapy as with vigabatrin (31.5% vs. 16.7%).

Speed of response. The median time to remission is significantly shorter with hormonal therapy (41 days) than with vigabatrin (142 days).

EEG resolution. Resolution of hypsarrhythmia at three months is significantly higher in children treated with ACTH (74%) or oral corticosteroids (83%) compared to those treated with vigabatrin (20%).

Literature meta-analysis. Aggregated data from multiple reviews show an 81% response rate with ACTH/corticosteroids, compared to 55% with vigabatrin in the trisomy 21 cohort.

Treatment timing: the urgency of intervention

"Lead time to treatment"—the delay between the first clinical spasm and treatment initiation—is a critical prognostic factor.

Diagnostic delays. In trisomy 21, diagnosis is often delayed because spasms are mistaken for hypotonia, gastroesophageal reflux, or normal "startle" responses.

Impact on outcomes. Each additional month of treatment delay is associated with 34% higher odds of developing Lennox-Gastaut syndrome and 51% higher odds of autism spectrum disorder.

Remission odds. Each month of delay increases the odds of prolonged remission or a complete lack of response by approximately 20%. Early treatment (within 30 days of onset) is essential to maximize developmental quotients.

Adverse events: comparing toxicity profiles

Clinicians must weigh efficacy against the significant side effect profiles of both standard modalities.

Hormonal side effects. Common reactions include weight gain, irritability, hypertension, and sleep disturbances. Serious infections requiring hospitalization have been reported in both monotherapy and combination therapy groups.

Vigabatrin side effects. Notable for MRI signal changes (restricted diffusion in the deep gray matter) and visual field defects. Data suggest that children with trisomy 21 may be more susceptible to vigabatrin-induced MRI changes, with one study reporting these changes in 54% of children imaged while taking the drug. Other effects include drowsiness, sedation, and movement disorders.

Comparisons with existing treatments and guidelines

ACTH versus oral prednisolone. Although North American centers often favor ACTH, evidence from the UKISS and other trials indicates that prednisolone (40 to 60 mg/day) is similarly effective, better tolerated by parents (oral vs. intramuscular), and significantly more cost-effective.

The case against first-line vigabatrin. Multiple studies now indicate that using vigabatrin as first-line monotherapy in trisomy 21is associated with less favorable outcomes, including higher relapse rates and a greater risk of subsequent epilepsy. Vigabatrin is best reserved as an add-on therapy for those who fail initial hormonal treatment.

Ketogenic diet. This should be considered early in refractory cases; some infants achieve remission on the ketogenic diet despite multiple medications failing.

Recent breakthroughs and ongoing controversies

Combination therapy (ICISS protocol). The ICISS trial showed that combining hormonal therapy with vigabatrin is superior to hormonal therapy alone in the general population of patients with infantile epileptic spasms syndrome (72% vs. 57% cessation). However, subgroup analysis of patients with trisomy 21 in the ICISS trial did not demonstrate a clear additional benefit of combination therapy over hormonal monotherapy.

Impact of initial treatment on long-term prognosis. This remains highly controversial. One extensive multicenter study found that although initial treatment (hormone vs. vigabatrin) impacted the time to remission, it did not significantly change the rates of ongoing epilepsy or autism spectrum disorder at 2-year follow-up. Conversely, other researchers argue that the lack of prompt initial control (as seen with vigabatrin) leads to a higher disease burden and poorer neurodevelopmental sequelae.

Trisomy 21 "better outcomes" myth. Although patients with trisomy 21 respond well acutely, clinicians should be cautious. One Irish cohort found that 25% had ongoing seizures and 85% had developmental concerns at follow-up, suggesting that the "favorable" outlook may be overstated.

Future directions and research gaps

Despite recent progress, significant gaps remain in our understanding and management of trisomy 21-associated infantile epileptic spasms syndrome.

Lack of randomized controlled trials. There are currently no randomized controlled trials specifically focused on the trisomy 21 population; most data come from retrospective cohort studies or subanalyses of larger trials.

Biomarkers for relapse. We urgently need biomarkers to identify children at high risk of relapse (approximately 25% of the trisomy 21 population) and of subsequent epilepsy.

Standardized EEG assessment. The low inter-rater reliability of hypsarrhythmia assessments threatens the validity of clinical trials. Moving toward standardized metrics, such as the BASED score, is necessary for future research.

Targeted therapies. Continued research into the GIRK2 pathway may lead to the development of nonhormonal, gene-specific treatments that could avoid the systemic side effects of steroids.

Clinical summary for practitioners

For an infant with trisomy 21 and new-onset spasms, hormonal therapy (ACTH or high-dose prednisolone) should be the first-line standard of care. Vigabatrin is significantly less effective as initial monotherapy and increases the risk of diagnostic and treatment delays. Because each week of delay is associated with poorer neurodevelopmental outcomes, immediate referral for EEG and initiation of hormonal therapy are the most critical actions a clinician can take. Clinical decisions should always be tailored to the individual patient.

References

Beatty CW, Wrede JE, Blume HK. Diagnosis, treatment, and outcomes of infantile spasms in the trisomy 21 population. Seizure 2017;45:184-8. PMID 28088035

Cao V, Chiu MY, Chellamani H, et al. Does first-line treatment impact outcomes in trisomy 21-associated infantile epileptic spasms syndrome? A multicenter North American analysis. Pediatr Neurol 2026;177:130-6. PMID 41689988

Chen H, Numis AL, Shellhaas RA, et al. Treatment efficacy for infantile epileptic spasms syndrome in children with trisomy 21. Front Pediatr 2025;13:1498425. PMID 40013114

Datta AN, Crawford J, Wong PK. Infantile spasms and trisomy 21: unfavorable outcomes with first-line vigabatrin therapy. Can J Neurol Sci 2021;48(6):839-44. PMID 33472713

Harvey S, Allen NM, King MD, et al. Response to treatment and outcomes of infantile spasms in Down syndrome. Dev Med Child Neurol 2022;64(6):780-8. PMID 35092693

Kats DJ, Roche KJ, Skotko BG. Epileptic spasms in individuals with Down syndrome: a review of the current literature. Epilepsia Open 2020;5(3):344-53. PMID 32913943

O’Callaghan FJ, Edwards SW, Dietrich Alber F. Safety and effectiveness of hormonal treatment versus hormonal treatment with vigabatrin for infantile spasms (ICISS): a randomised, multicentre, open-label trial. Lancet Neurol 2017;16(1):33-42. PMID 27838190

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