Evaluation of neuromuscular tone phenotypes in children with autism spectrum disorder: An exploratory study

Motor disorders are known in autism spectrum disorder (ASD), but muscle tone assessments are rarely performed. Muscle tone underpins movement. We investigated muscle tone in 34 ASD children using a standardized neuro-developmental battery, which uses the French norms for muscular tone in children.

Dangling and extensibility were used to examine passive muscle tone in the upper and lower limbs and the body axis. A comparison between muscles of the right and left sides enabled the determination of tonic laterality.

We found a disharmonious tonic typology, with a tonic component for the muscles of the trunk and the proximal muscles of the lower limbs and a laxity component for the ankles and the proximal and distal muscles of the upper limbs (wrists and shoulders). No establishment of tonic laterality was found in the upper limbs in 61% of ASD children (P<0.001).

The disturbed tonic organization influenced by subcortical structures, such as the cerebellum, may partially explain the motor disorders, and indefinite tonic laterality may also be linked to low hemispheric brain dominance described in autism. This preliminary examination is necessary before any gross motor assessments to understand the nature of movement disorders, explore typologies and highlight possible soft neuro-motor signs.