Abstracts

Rationale: Dravet syndrome is an increasingly recognised severe infantile-onset epilepsy syndrome associated with SCN1A mutations in 70% cases. Seizures are most severe in the first decade but gait often deteriorates in the second decade of life. Adults with Dravet syndrome may not be able to independently ambulate over long distances. The nature of the gait deterioration has not been well characterised. Methods: 13 patients with Dravet syndrome underwent a standardized physical examination by a physiotherapist with experience in neuromuscular disorders, completion of a functional mobility scale, two dimensional videography and radiographs of the pelvis and feet. Results: Patients were studied between 4y 9m and 22y 11m (median 11.5y). A characteristic gait pattern was observed which was present to some degree in all subjects but with much more severe expression in those who were skeletally mature, post-pubertal growth spurt. Analysis in the sagittal plane showed the evolution of a crouch gait pattern with age. In the coronal plane, severe malalignment was observed consisting of three components: inset hips, (medial femoral torsion), lateral tibial torsion and external foot progression because of pes abductovalgus. Hip radiographs showed very mild and subtle abnormalities only, there was no frank subluxation. However standing foot radiographs consistently showed mid-foot breaching and increased talo-calcaneal angles outside the normal range. Ataxia was not observed.Conclusions: Children with Dravet syndrome show minor gait abnormalities in early childhood with a high level of independence and physical functioning. However with time and puberty, bone remodelling results in a consistent biomechanical malalignment associated with torsion of the long bones. This results in a progressive crouch gait and deterioration in physical functioning and independence. Early identification of changes may enable strategies to prevent progression. The sodium channel mutation is likely to underpin the neurobiological mechanism causing the characteristic musculoskeletal changes.