Parents and teachers typically suspect a child has autism when communication skills including speech, following directions and ability to interpret nonverbal cues are delayed. However, children with autism also may exhibit physical symptoms, including decreased hand strength and muscle tone, repetitive hand movements such as flapping and poor eye-hand coordination. In addition, children with autism may demonstrate an aversion to touching objects and being touched, which affects hand development.
Many children with autism demonstrate difficulties processing sensory information. The term "tactile defensive" refers to one symptom of sensory integration dysfunction in which the person finds touch aversive. Signs of tactile defensiveness may include: avoiding touching paint, gooey food or glue or interpreting the touch of a hair brush bristle as painful. Babies with tactile defensiveness may avoid crawling because they interpret touch to their palms as painful; they may cry when placed on sand or grass. Missing out on these important early sensory experiences affects hand development.
Decreased Hand Strength and Low Muscle Tone
Children with autism often have decreased strength and low muscle tone that makes them appear floppy like a rag doll. They frequently slide out of their seats, flop onto their bellies and have hands that just feel "mushy." Because these children may avoid using their hands to engage in strengthening activities such as molding clay, squeezing glue bottles or pushing Tinker Toy parts together, their hands lack strength and their hand arches are flat.
Children with autism may not engage in fine-motor activities due to distractibility, a preference for gross motor activities and coordination challenges that make it difficult to achieve success when using early learning tools such as crayons, scissors or lacing boards. Some children with autism engage in repetitive hand activities such as lining up trucks or stacking boxes that have limited value in strengthening hands and developing dexterity.
Self-Stimulatory Hand Movements
Some individuals with autism may engage in repetitive, stereotypic movements with their hands, including flapping, moving fingers in front of the eyes, pulling hair, thumb sucking, nail biting or picking on various body parts. These behaviors are called self-stimulatory; when they cause injury they are called self-injurious behaviors, or SIB. It is theorized that due to sensory integration dysfunction, some individuals crave the sensory stimulation provided by these behaviors. Another theory is that if a person is experiencing sensory overload from the environment, the behaviors provide a way to tune out the offending stimuli.
Atypical Manipulation Skills
Individuals with autism and other developmental disabilities may demonstrate atypical grasp patterns and manipulation skills resulting from tactile defensiveness and decreased hand strength, muscle tone and coordination. They may use their fingertips to grasp a hairbrush or spoon and avoid stabilizing work materials such as paper while writing. Individuals with autism often benefit from activities that are adapted to provide sensory stimulation, such as use of a weighted or vibrating pen, or compensate for poor coordination, such as using a lacing board with extra large holes.