Dysmetria () is a lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye. It is a type of ataxia. It can also include an inability to judge distance or scale.
Hypermetria and hypometria are, respectively, overshooting and undershooting the intended position.
Presentation
Associated diseases
Dysmetria is often found in individuals with multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and persons who have had tumors or strokes. Persons who have been diagnosed with autosomal dominant spinocerebellar ataxia (SCAs) also exhibit dysmetria. There are many types of SCAs and though many exhibit similar symptoms (one being dysmetria), they are considered to be heterogeneous. Friedreich's ataxia is a well-known SCA in which children have dysmetria. Cerebellar malformations extending to the brainstem can also present with dysmetria.
Causes
The actual cause of dysmetria is thought to be caused by lesions in the cerebellum or by lesions in the proprioceptive nerves that lead to the cerebellum that coordinate visual, spatial and other sensory information with motor control. Damage to the proprioceptive nerves does not allow the cerebellum to accurately judge where the hand, arm, leg, or eye should move. These lesions are often caused by strokes, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), or tumors.
According to the research article cited above, motor control is a learning process that utilizes APPGs. Disruption of APPGs is possibly the cause of ataxia and dysmetria and upon identification of the motor primitives, clinicians may be able to isolate the specific areas responsible for the cerebellar problems.
There are two types of cerebellar disorders that produce dysmetria, specifically midline cerebellar syndromes and hemispheric cerebellar syndromes. Midline cerebellar syndromes can cause ocular dysmetria, a condition in which the eyes can not track an object properly and either overshoot (ahead of the object )or undershoot (lagging behind the object). Ocular dysmetria also makes it difficult to maintain fixation on a stationary object. Hemispheric cerebellar syndromes cause dysmetria in the typical motor sense that many think of when hearing the term dysmetria.
A common motor syndrome that causes dysmetria is cerebellar motor syndrome, which also marked by impairments in gait (also known as ataxia), disordered eye movements, tremor, difficulty swallowing and poor articulation. As stated above, cerebellar cognitive affective syndrome (CCAS) also causes dysmetria.
Anatomy
The cerebellum is the area of the brain that contributes to coordination and motor processes and is anatomically inferior to the cerebrum. Sensorimotor integration is the brain's way of integrating the information received from the sensory (or proprioceptive) neurons from the body, including any visual information. To be more specific, information needed to perform a motor task comes from retinal information pertaining to the eyes' position and has to be translated into spatial information. Sensorimotor integration is crucial for performing any motor task and takes place in the post parietal cortex. After the visual information has been translated into spatial information, the cerebellum must use this information to perform the motor task. If there is damage to any pathways that connect the pathways, dysmetria may result.
Motor
Motor dysmetria is the customary term used when a person refers to dysmetria. Dysmetria of the extremities caused by hemispheric syndromes is manifested in multiple ways: dysrhythmic tapping of hands and feet and dysdiadochokinesis, which is the impairment of alternating movements. Damage to the cerebellum makes a person slow to orient their extremities in space.