Dysmetria ( en, wrong length) 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 Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...

. It can also include an inability to judge distance or scale.

Hypermetria Dysmetria ( en, wrong length) 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. ...

and

hypometria Dysmetria ( en, wrong length) 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. ...

are, respectively, overshooting and undershooting the intended position.

Presentation

Associated diseases

Dysmetria is often found in individuals with

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

(MS),

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

(ALS), and persons who have had

tumors A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

s. Persons who have been diagnosed with

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

dominant

spinocerebellar ataxia Spinocerebellar ataxia (SCA) is a progressive, degenerative, genetic disease with multiple types, each of which could be considered a neurological condition in its own right. An estimated 150,000 people in the United States have a diagnosis of s ...

(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 Friedreich's ataxia (FRDA or FA) is an autosomal-recessive genetic disease that causes difficulty walking, a loss of sensation in the arms and legs, and impaired speech that worsens over time. Symptoms generally start between 5 and 20 year ...

is a well-known SCA in which children have dysmetria. Cerebellar malformations extending to the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

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 Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...

nerves does not allow the cerebellum to accurately judge where the hand, arm, leg, or eye should move. These lesions are often caused by

(MS),

(ALS), or

. 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 Ocular dysmetria is a form of dysmetria that involves the constant under- or over-shooting of the eyes when attempting to focus gaze on something. Ocular dysmetria indicates lesions A lesion is any damage or abnormal change in the tissue of an ...

, 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 Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Di ...

(also known as

), disordered eye movements,

tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...

, difficulty

swallowing Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing i ...

and poor articulation. As stated above, cerebellar cognitive affective syndrome (CCAS) also causes dysmetria.

Anatomy

The

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

is the area of the brain that contributes to coordination and motor processes and is anatomically inferior to the

cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...

. 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 Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision). Some microorganisms use retin ...

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 Rhythm (from Greek , ''rhythmos'', "any regular recurring motion, symmetry") generally means a " movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions". This general meaning of regular rec ...

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. Motor control as a learning process Recent research has also shed light upon a specific process that if interrupted, may be the cause of

and dysmetria. According to sources cited in this article,

motor control Motor control is the regulation of movement in organisms that possess a nervous system. Motor control includes reflexes as well as directed movement. To control movement, the nervous system must integrate multimodal sensory information (both f ...

is a learning process that occurs in the

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

s of Purkinje

dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...

s. There have been varying theories as to the makeup of the cerebellum, which controls this process. Some predicted that the cerebellum was an array of adjustable pattern generators (APGs), each of which generate a "burst command" with varying intensity and duration. Other models, which apply mostly in

robotic Robotics is an interdisciplinarity, interdisciplinary branch of computer science and engineering. Robotics involves design, construction, operation, and use of robots. The goal of robotics is to design machines that can help and assist human ...

applications, propose that the cerebellum acquires an "inverse model of the motor apparatus". More recent research in

electrophysiology Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , '' -logia'') is the branch of physiology that studies the electrical properties of b ...

has shown modular structures in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

known as "motor primitives". Based on the APG model, modules of APG are the features that control

motor learning Motor learning refers broadly to changes in an organism's movements that reflect changes in the structure and function of the nervous system. Motor learning occurs over varying timescales and degrees of complexity: humans learn to walk or talk over ...

. The entire process is a

positive feedback loop Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...

. Inhibitory input is transmitted and received from various components of the

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

, including the

cerebellar nucleus The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

, a motor cortical cell and

Purkinje cell Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech people, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839. Stru ...

s. Purkinje cells send the inhibitive information by obtaining learning information from parallel fibers of

granule cells A granule is a large particle or grain. It can refer to: * Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown function ** Azurophilic granul ...

. This model of APGs is useful in that it effectively describes the motor learning process. Motor primitives are another proposed module of motor learning. This information was found by electrical stimulation of the

lumbar spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal ...

in rats and frogs. Upon the stimulation, researchers found that motor primitives are found in the

and use patterns of

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

activation to generate a specific motor output. Different movements are learned from different levels of activation. These findings led researchers to believe that these same motor primitives could be found in the cerebellum. These two different models combined show that it is possible that motor primitives are in the cerebellum, because, "a set of parallel arrays of APG can drive each motor primitive module in the spinal cord." The authors have generated a model of adjustable primitive pattern generator (APPG), which is basically a group of parallel APGs summed together. The APPG model is a vector sum of all the inputs of the APG, which are units of position, velocity and time.

Granule cells A granule is a large particle or grain. It can refer to: * Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown function ** Azurophilic granul ...

send information from the spinal cord and the

motor cortex The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately a ...

which in turn translates the information in a process called state mapping. The final model of the APPG becomes linear upon the vector summation of the information from the

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s and muscles. This model is consistent with the "virtual trajectory hypothesis" which states that the desired trajectory is sent to the spinal cord as a motor command.

Saccadic

Saccades A saccade ( , French for ''jerk'') is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishi ...

are the very quick, simultaneous movements made by the eye to receive visual information and shift the line of vision from one position to another. A person depends profoundly on the ability of the accuracy of these movements. The information is received from the retina, is translated into spatial information and is then transferred to motor centers for motor response. A person with saccadic dysmetria will constantly produce abnormal eye movements including microsaccades, ocular flutter, and square wave jerks even when the eye is at rest. During eye movements hypometric and

hypermetric In poetry, metre ( Commonwealth spelling) or meter ( American spelling; see spelling differences) is the basic rhythmic structure of a verse or lines in verse. Many traditional verse forms prescribe a specific verse metre, or a certain set of ...

saccades will occur and interruption and slowing of normal saccadic movement is common.

Diagnosis

Diagnosis of any cerebellar disorder or syndrome should be made by a qualified

neurologist Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal c ...

. Prior to referring a patient to a neurologist, a general practitioner or MS nurse will perform a finger-to-nose test. The clinician will raise a finger in front of the patient and ask him to touch it with his finger and then touch his nose with his forefinger several times. This shows a patient's ability to judge the position of a target. Other tests that could be performed are similar in nature and include a heel to shin test in which

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

overshoot characterizes dysmetria and an inability to draw an imaginary circle with the arms or legs without any decomposition of movement. After a positive result in the finger-to-nose test, a neurologist will do a

magnetic resonance image Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

(MRI) to determine any damage to the cerebellum. Cerebellar patients encounter difficulties to adapt to unexpected changes of the inertia of the limbs. This can be used to increase dysmetria and confirm a diagnosis of cerebellar dysfunction. Patients also show an abnormal response to changes in damping. These findings confirm a role of the cerebellum in predictions.

Treatments

Currently there is no cure for dysmetria itself as it is actually a symptom of an underlying disorder. However,

isoniazid Isoniazid, also known as isonicotinic acid hydrazide (INH), is an antibiotic used for the treatment of tuberculosis. For active tuberculosis it is often used together with rifampicin, pyrazinamide, and either streptomycin or ethambutol. For l ...

and

clonazepam Clonazepam, sold under the brand names Klonopin and Rivotril, is a medication used to prevent and treat seizures, panic disorder, anxiety disorders, and the movement disorder known as akathisia. It is a tranquilizer of the benzodiazepine clas ...

have been used to treat dysmetria.

Frenkel exercises Frenkel exercises are a set of exercises developed by Professor Heinrich Sebastian Frenkel to treat ataxia, in particular cerebellar ataxia. They are a system of exercises consisting of slow, repeated movements. They increase in difficulty over t ...

treat dysmetria.

Research

Researchers now are testing different possibilities for treating dysmetria and

. One opportunity for treatment is called rehearsal by eye movement. It is believed that visually guided movements require both lower- and higher-order visual functioning by first identifying a target location and then moving to acquire what is sought after. In one study, researchers used visually guided stepping which is parallel to visually guided arm movements to test this treatment. The patients had saccadic dysmetria which in turn caused them to overshoot their movements 3. The patients first walked normally and were then told to twice review the area that was to be walked through 3. After rehearsal with eye movements, the patients improved their motor performance. Researchers believe that prior rehearsal with the eyes might be enough for a patient with motor dysmetria as a result of saccadic dysmetria to complete a motor task with enhanced

spatial awareness Spatial contextual awareness consociates contextual information such as an individual's or sensor's location, activity, the time of day, and proximity to other people or objects and devices.Chen, Guanling, and David Kotz. 2000. A Survey of Context- ...

. Research has also been done for those patients with MS. Deep brain stimulation (DBS) remains a viable possibility for some MS patients though the long-term effects of this treatment are currently under review. The subjects who have undergone this treatment had no major relapse for six months and disabling motor function problems. Most subjects benefited from the implantation of the

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

and some reported that their movement disorder was gone after surgery. However, these results are limiting at this time because of the small range of subjects who were used for the experiment and it is unknown whether this is a viable option for all MS patients with motor control problems.

References

External links

{{Nervous and musculoskeletal system symptoms and signs Symptoms and signs: Nervous system