Background
Movement clumsiness has gained increasing recognition as an important condition of childhood. However, its diagnosis is uncertain. Approaches to assessment and treatment vary depending on theoretical assumption about etiology and its developmental course.
During the last century, many terms have been used to describe children with clumsy motor behavior. Variation in labeling has been systematically different and has depended on cultural and/or professional backgrounds. For example, medical professionals use medical terms (eg, clumsy child syndrome, minimal brain dysfunction), whereas educational professionals use educational terminology (eg, poorly coordinated children, movement-skill problems, physical awkwardness). A variety of labels include assumptions about the etiology. Examples include developmental dyspraxia (which suggests underlying difficulties in motor planning), perceptual motor difficulties (which suggests problems in perceptual motor integration), minor neurologic dysfunction (MND), and sensory integrative dysfunction.
Although heterogeneity in labels is confusing and counterproductive, participants at an international multidisciplinary consensus meeting in 1994 agreed to use the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM IV) term developmental coordination disorder (DCD).[1] Although subsequent debate has emerged on several issues in the DSM IV definition, such as the construct of the term coordination, or what constitutes impaired functioning (both of which are in the current definition of DCD in the DSM IV), researchers and clinicians are increasingly accepting the use of a term that is "atheoretical."
The 4 DSM IV diagnostic criteria for DCD are as follows:
- Performance in daily activities that require motor coordination is substantially below given the person's chronologic age and measured intelligence. This change may manifest as marked delays in achieving motor milestones (eg, walking, crawling, sitting) and as dropping things, clumsiness, poor performance in sports, or poor handwriting.
- The disturbance in criterion 1 substantially interferes with academic achievement or activities of daily living.
- The disturbance is not due to a general medical condition (eg, cerebral palsy, hemiplegia, muscular dystrophy), and it does not meet criteria for a pervasive developmental disorder.
- If mental retardation is present the motor difficulties are in excess of those usually associated with it.
Little data clearly define the parameters of motor coordination difficulties in children. Various grades of severity and comorbidity seem to exist. Some children have only a relatively minor form of motor dyscoordination, whereas others have associated learning disabilities, attention deficit, and other difficulties.
In 1996, Fox and Lent found that, in contrast to the common belief that children grow out of these difficulties, they tend to linger without intervention.[2] Early intervention is beneficial while the brain is changing dramatically during the first years of life and new connections and abilities are acquired.
Children with multiple conditions are at greatest risk of developing behavioral difficulties over time. Some evidence supports dividing DCD into subtypes based on main features such as manipulating objects, the speed of movement, catching objects (eg, balls during sports activities), or writing ability.
A discussion about including DCD, as currently defined, into the cerebral palsy category was held.[3] This inclusion would put DCD on the low end of the continuum of neuromotor disabilities, also described as minimal cerebral palsy.
Pathophysiology
Motor coordination is the product of a complex set of cognitive and physical processes that are often taken for granted in children who are developing normally. Smooth, targeted, and accurate movements, both gross and fine, require the harmonious functioning of sensory input, central processing of this information in the brain and coordination with the high executive cerebral functions (eg, volition, motivation, motor planning of an activity). Also required is the performance of a certain motor pattern. These elements must work in a coordinated and rapid way to enable complex movements involving different parts of the body.
Our understanding of motor development in humans and its pathophysiology of motor clumsiness is only in its infancy. Because of its heterogeneity in presentation and definition, finding its cause has been difficult.
A variety of theoretical models explain the role of the nervous system in motor development.
In the traditional primitive reflex model (neuromaturational theory), higher centers exert increasing control over lower reflexes. In the dynamic systems model, the CNS interprets sensory feedback, and the appropriate movement strategy is selected on the basis of current experience, on the state of the internal and external environment, and on one's memory of similar movements.
In the more recent neuronal group–selection theory, aspects of both models are combined. Functional groups of neurons exist on all levels of the CNS. These groups are determined by evolution, but their functional integrity depends on afferent information produced by movement and experience. In both cortical and subcortical structures, these neuronal groups serve as early repositories for motor behavior or the receipt of specific sensory information.
Motor development is described in 2 phases. The first phase of primary variability is characterized by crude and erratic motor activity that does not require sensory information for its initiation or guidance. These self-generated movements give rise to afferent (visual, kinesthetic) inputs that reinforce more specific synaptic connections in each group. In the second phase, sensory and motor factors interact, resulting in specific and complex muscle contraction patterns that characterize coordinated, goal-directed movement. As increasing efficient movement patterns are practiced, appropriate synaptic circuits are reinforced and subsequently established.
Adequate realization of a motion or sequence of movements requires the convergence of numerous pathways and a central system in charge of integrating the information. The motor cortex, cerebellum, and vestibular system (which provides input about directionality, gravity, motion) are all part of this central mechanism. Proprioceptive information (ie, sensation of where the body is in space and about the positions of the limbs and parts of the body), visual input (ie, where the body is in space and where it should go), and an adequate degree of alertness (ie, the reticular formation activated to an optimal degree) all provide information to the CNS. If one of these systems is not functioning adequately, the resulting planned movement may not be satisfactory or smooth.
Discussed in this article are some of the building blocks of motor functioning that are important in understanding difficulties with motor skills, their maturation, and the evaluation of children who struggle with these challenges. Main elements in this chain of events are discussed.
Muscular tone
Muscular tone refers to the basic and constant ongoing contraction or muscular activity in the muscles. It can be understood as a baseline or background level. Tone may be normal, too low, or too high. Hypotonic children appear floppy. For example, hypotonic babies have an appearance similar to a rag doll. Infants or young children who may be hypotonic have difficulty maintaining posture against gravity and prefer to sit, leaning against something, or they may prefer to lie on the floor. Preschool-aged children may sit in a fashion that appears lazy. Rather than sitting upright, they mostly sit in a slouching manner, leaning on the chair or a table with their head over the top of the table, or they may lie down during activities as much as possible. Of course, this positioning can also be observed in older children and is often erroneously interpreted as a sign of lack of interest or even disrespect.
By contrast, when muscular tone is too high (hypertonic), children appear somewhat stiff and do not move in a smooth and natural way. Youngsters may move somewhat like a puppet or robot, and they lack the ordinarily smooth nature of movement in small motor acts.
Basic muscle tone that is too low or too high is one of the components of impaired motor skills. Children must fight low muscular tone to carry out movements, expending energy to maintain postures and activities. Hypertonic children may make many mistakes because of the overactivation of the muscular units.
Gross motor skills
Gross motor skills refer to the ability of children to carry out activities that require large muscles or groups of muscles. Muscles or groups of muscles should act in a coordinated fashion to accomplish a movement or a series of movements. Examples of gross motor tasks are walking, running, throwing something, jumping, standing on 1 leg, playing hopscotch, and swimming. Posture is an important element to consider in the assessment of gross motor skills. Adequate posture may make all the difference between being able or not able to execute a movement. This is particularly true in infants and young children. Six-month-old infants may be able to reach for a toy if sitting, but they may be unable to organize this movement if their trunk is tilted or straining to maintain a vertical position.
Fine motor skills
Fine motor skills consist of movements of small muscles that act in an organized and subtle fashion, for instance, the hands, feet, and muscles of the head (as in the tongue, lips, facial muscles), to accomplish more difficult and delicate tasks. Fine motor skills are the basis of coordination, which begins with transferring from hand to hand crossing the midline when aged 6 months. Examples of fine motor activities are writing, sewing, drawing, putting a puzzle together, imitating subtle facial gestures, pronouncing words (which involves coordination of the soft palate, tongue, lips), blowing bubbles, and whistling. Many children who have difficulties in their fine motor skills also have difficulties in articulating sounds or words.
Muscular strength
Muscular strength refers to the intensity of the muscle contraction exerted voluntarily that may be required to carry out an activity. Some children who struggle with motor clumsiness appear weak and slender and may have an inadequate strength in their movements.
On the other end of the continuum, they may appear strong and muscular. For instance, children with hypertonicity in the leg muscles, who may tend to walk on their tiptoes, may develop a higher muscular mass in the leg muscles to maintain the tiptoe position. Children who are too strong often appear brusque in their movements. Instead of softly caressing someone on the face, they may involuntarily slap the person when they are attempting to show affection. The same occurs while giving a hug, which to others may feel more like a squeeze or like being physically crushed in the child's unintentional hypertonic grip.
By contrast, a youngster with diminished muscular strength appears floppy or scrawny with thin arms, forearms, and legs. These children may execute movements that other children take for granted only at great cost. Shaking the child's hand and asking him or her to squeeze the clinician's hand are techniques to assess the child's strength. Hypotonic children cannot apply much pressure in a handshake; therefore, their handshake feels weak. They fatigue easily and claim to be unable to carry out simple tasks. For example, they may write with only thin lines and barely visible traces, and the pencil may slip out of their hand too easily.
Motor planning
Motor planning consists of the ability of children to imagine a mental strategy to carry out a movement or an action; for instance, how to get on top of a table, how to move from point A to point B and overcome some obstacle, how to execute a dance step, or learning how to skip. Typical youngsters develop some preconscious planning in the sequencing of movements, including how the body and limbs coordinate, the amount of strength required, and the necessary steps needed to achieve a specific goal.
Most of the time in unaffected children, this function is achieved intuitively and without conscious planning. However, when children have difficulties in motor planning, they carry out movements using odd strategies; for instance, trying to reach something that is out of reach without getting up from a previous position. Another example is a child trying to get down from a chair without moving the trunk and preparing himself to go down and instead just letting himself fall. When these problems exist, parents notice that the child may fall just standing, or such children frequently fall from a chair or stool. The child seemingly lacks the intuitive ability to plan how to effect a movement.
Motor planning involves a number of abilities, including the visual detection of motion and errors in movement, selection of responses, and self-corrective motions. Movements must be timed adequately, and attention and concentration are also necessary.
Sequencing and speed of movements
Sequencing and speed of movements involves the order in which movements should proceed one after the other to accomplish a desired goal. This order is mostly unconscious or intuitive. When children try to manage a complex motor act or imitate something that has been modeled, their ability to do a series of movements may be compromised. These children often have problems in other activities that might require sequencing, such as in reading, writing their ideas, or even continuous speech.
Children with difficulties in motor skills often perform movements slowly as a result of their difficulty in organizing and coordinating motion. They may also rely on visual cues to perform the movement (eg, in handwriting) more than other children do. The necessity to view the movement slows the performance.
Sensory integration
Sensory integration refers to functioning of the brain, ie, how it manages input and produces output. Outputs include motor responses. Jean Ayres proposed this theory, which many authors, mostly in the field of occupational therapy but also in mental health, have further developed.[4]
The central concept is that children may struggle to integrate sensory input (eg, visual, auditory, tactile, and proprioceptive cues) and develop aversions (eg, to being touched, to being exposed to new sounds). Also, children may become overstimulated in any of these sensory channels, and their behavior and motor performance deteriorate in circumstances of overstimulation. Each child has a unique profile of responses to sensory stimuli. Children with motor difficulties often have problems in the integration of sensory input, which make them vulnerable to problems resulting from sensory stimulation.
Epidemiology
Frequency
United States
Few groups have examined the prevalence of motor skills disorders in an open population. Approximately 4-6% of children of school age struggle with motor difficulties to the degree that causes concern to them and those around them.
International
In 1998, Kadesjo and Gillberg found that motor coordination disorder frequently coexisted with poor attention span and concentration and that it was comorbid in about 6.1% of children in a sample of 409 nonreferred children in Sweden. Both disorders tended to remain stable, persisting on follow-up 8 months later. Boys were affected more frequently than girls.[5]
In a 1996 study in Singapore by Wright and Sugden, 4% of children aged 6-9 y who were randomly sampled had difficulties in motor coordination. This study included only children with impairment in motor skills that notably interfered in their functioning in everyday life.[6]
According to studies in different countries, the prevalence of motor coordination disorders varies widely. In some studies, rates are higher than that in the United States. For instance, in the United Kingdom, 10% of all children reportedly have motor coordination difficulties. A conservative estimate suggests that 5% of children have the disorder worldwide; an additional 10% of children may have a minor form of the problem.
Mortality/Morbidity
The disorder does not directly lead to mortality. The incidence of accidents may be increased in children who have motor challenges, because of clumsiness, for example. However, this clumsiness has not been documented to raise the mortality rate.
Race
No evidence indicates an increased or decreased frequency of the condition according to racial groups.
Sex
Boys are thought to be affected more frequently than girls, though this possibility has not been systematically studied.
Age
Disturbances in motor abilities are most evident during school age as children face challenges such as physical education, sports, and writing. In many cases, children with motor coordination disturbances present at an early age, and motor coordination disturbances may be detected in children younger than school age.
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