Characteristics of Dravet Syndrome

Dravet Syndrome is a clinical diagnosis, based on recognition of seizure types, the clinical course of the condition (e.g. developmental delays, comorbidities), and electroencephalographic (EEG) features.

Recent research suggests that the earlier Dravet Syndrome is diagnosed, the better the longer outcomes. It is also important to recognise that no matter the age of the patient (from infancy to late adulthood), diagnosis and the right treatment plan can change their life. It can mean less seizures, improved quality of life for them and their family, better management of comorbidities and improved intellectual outcomes. 

Typical characteristics of Dravet Syndrome include:

Age of the first seizure

• Typically between 3 to 9 months, with an average of 6 months
• Rarely, some children can present as early as one month old or as late as 20 months
• The child will previously be well, developmentally normal

Initial types of seizure include:

• Febrile seizure, often hemiclonic, generalised clonic/tonic, status epilepticus (>30 minutes) may occur
• Triggered by high temperature or water.

Normal development during first year of life

• Development slows, walk a little later (e.g. 17–18 months)
• Unsteady for longer
• Language slower to acquire; sometimes regress

EEG usually normal in first 1–2 years 

• Around 50% of children with Dravet Syndrome, who are between one and four years old, will have an abnormal EEG
• After first 1-2 years, EEG may show a generalised spike wave, polyspike, multifocal discharges, may be photosensitive
• IN Dravet Syndrome, EEG results need to be looked at in the context of other symptoms and characteristics and, ideally, a genetic test

In the second year myoclonic and atypical absences may appear

• Other seizure types emerging from the second year include: myoclonic seizures, focal seizures with impairment of awareness (complex partial/dyscognitive seizures), atypical absence seizures, atonic seizures

After 2–5 years, episodes of status settle

• Convulsive status much less frequent but can still occur; TCS evolve to focal seizures with impairment of awareness and then primarily nocturnal generalised clonic/tonic seizures
• Myclonia more prominent as older, may fluctuate or become more prolonged

Seizure frequency high in the first decade of someone’s life

• They may stabilise after 10 but seizure patterns may change again with puberty
• Being seizure-free is rare
  

Long-term development

• Gait: A deterioration of walking ability after the age of 10. Unusual crouch gait may appear after 13 years (bony malalignment with significant functional impairment)
• Physiological ataxia does not improve in normal time course, pyramidal signs develop
• Intellectual disability (severe 50%, moderate 25%, mild 25%) with impaired cognitive and adaptive functioning; children and adults are long-term dependent, requiring 24/7 supervision and care (often 2:1)
• Children can develop features of autism, with some showing attention problems and/or challenging behaviour
• Sleep disruption is observable in the majority of patients (as well as nocturnal seizures)
• Growth and nutrition issues including potential difficulties with swallowing, appetite and  weight loss; gastrostomy may be required for some
• Other difficulties include frequent infections (e.g. ear, nose, throat, lung and digestive) and dysautonomia
  

Adults with intellectual disability and epilepsy

• Dravet Syndrome is a life-time condition. Don’t rule out Dravet Syndrome. The right diagnosis and treatment can still reduce seizure and disease burden even in intractable adult patients

The above information is a brief summary of the key characteristics of Dravet Syndrome. For more detail on the typical presentation of seizures, developmental delay/intellectual disability and other comorbidities, click on the links below. 

Essential reading:

In 2022, the ILAE updated the classification and definition of Dravet Syndrome. This is included in:

• Sameer M. Zuberi et al. ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions, Epilepsia 2022