Given that the most common causes of developmental delay affect the brain diffusely (eg, chromosomal/genetic syndromes), delays in motor development are most commonly a component of more globally delayed developmental milestones across neuromotor, neurocognitive, and neurobehavioral streams of development. Thus, when a child presents with a chief complaint of delays in motor development, a thorough developmental history is needed to uncover possibly more subtle delays in language, nonverbal/visual-motor problem-solving, social, or adaptive development. However, there is a spectrum of dissociated and deviated motor development, where motor development is discrepantly delayed compared to other domains in development, and in more severe cases, where motor skills are acquired in a developmentally deviated manner (see Chapter 83). This chapter will review the motor disabilities contained within this spectrum of discrepant (or dissociated and deviated) motor delay.
Embryologically, the neural system is one of the earliest to begin to develop and the last to be completed. This system develops in a predictable manner of progression from cephalad to caudal and proximal to distal, as do motor skills after birth. A deviation from this predicted pattern may represent the earliest signs of a future motor delay or disability. Motor disorders can be central or peripheral in origin. Understanding patterns of typical development will aid the clinician in appropriately diagnosing and treating the underlying condition.
Motor skills are not as correlated as other domains of development are to overall cognitive function, but when delayed, they are the most evident early on. When severe, these delays not only are obvious to clinicians but also are evident to family members. However, subtle differences in motor development may or may not predict an actual disorder. Therefore, it is important to remember that there is a wide range of normal variation in motor development, and even typically developing children may achieve motor milestones at different times. Since a motor delay can be particularly anxiety provoking to family members, it is imperative to approach these concerns in a caring manner, be able to explain the observations in family-centered language, and provide reassurance when appropriate.
In addition to identifying a discrepant delay (dissociation) or deviation in motor development, it is imperative that a clinician assess the nature of the disorder and evaluate for potential associated medical conditions and complications. Even when a definitive diagnosis cannot be obtained early on, timely identification of delays should prompt referrals to therapeutic services, which may improve the ultimate function and quality of life for children with motor disabilities.
PATHOGENESIS AND EPIDEMIOLOGY
While motor development most often occurs in a predictable pattern, a delay, dissociation, or deviation from this pattern is most often, but not always, indicative of an underlying diagnosis. While motor delay is required for a motor disability diagnosis, deviation from the typical pattern of development does not always represent a problem (eg, walking before crawling). However, if ...