University of Groningen
Towards understanding infants' early motor repertoire
Salavati, Sahar
DOI:
10.33612/diss.167712103
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Publication date:
2021
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Citation for published version (APA):
Salavati, S. (2021). Towards understanding infants' early motor repertoire: the exploration of a diagnostic
and prognostic tool. University of Groningen. https://doi.org/10.33612/diss.167712103
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Chapter
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GENERAL INTRODUCTION
The origin of the assessment of the infant’s spontaneous movements
Since its introduction by Prechtl in 1990,1 non-invasive, neurological assessment of
the general movements (GMs) of young infants has become increasingly popular among neonatologists and paediatricians.2 The method focuses on assessing the
infant’s endogenously generated patterns of movements. Merely by observing these spontaneous movements and assigning a score, insight can be gained into the integrity of the infant’s central nervous system. Several years after its introduction, the assessment of GMs was enhanced by assessing additional distinct movements and postures, both qualitative and quantitative. The two assessments combined were referred to as the early motor repertoire.3 Repeatedly, during the past years,
the early motor repertoire has demonstrated its worth as a valuable predictor of neurodevelopment.4–6 Initially, the focus was mainly on the motor development
of infants at risk of cerebral palsy (CP). Later, this was extended to other groups of infants who were at risk, high or low, of poor neurodevelopment. More or less simultaneously the question arose whether, apart from their association with motor development, these spontaneous movements might also be associated with other neurodevelopmental domains.
Underlying neural mechanisms
The infant’s spontaneous movements are generated by a neural network that consists of so-called central pattern generators (CPGs), which generate rhythmic motor patterns without any oscillatory input.7–9 Studies in anencephalic foetuses
indicated that the CPGs are located in the brainstem. It was reported that ultrasound imaging of these foetuses shows various patterns of spontaneous movements that are, however, monotonous and non-fluent.10,11 Under normal circumstances CPGs
are modulated by supraspinal projections and sensory feedback. Such modulations result in sequences of variable, fluent, and complex movements. Prior to a post-term age (PTA) of 3 months, the cortical subplate could play a role in modulating GMs.12
At approximately 3 months of PTA, a major neural transformation occurs and the subplate disappears.12,13 This phase is characterized by increased activity of cortical
structures.14 At the end of the second month after term, the appearance of the GMs
change into so-called fidgety movements (FMs), which are apparently triggered by a different CPG than that of the GMs that came before. After this major neural transformation, permanent cortical and subcortical structures such as white matter are, at least partly, responsible for modulating the FMs.12 Several studies support this
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view by demonstrating that abnormalities in GMs and FMs are associated with white matter abnormalities in very preterm infants.15,16
Details of the assessment of the early motor repertoire
General movements are regarded as the keystone of the early motor repertoire. These endogenously generated movements are already present in utero and their characteristics gradually change along with the early development from foetus to young infant. In the same way as foetal movements serve to assess the wellbeing of the foetus 17–19, so the quality of spontaneous movements in the first few months
after birth can be used to determine the infant’s neurological status.3 The early motor
repertoire is assessed by observing video recordings of 2 to 5 minutes during which the infant is in a state of active wakefulness and not distracted by its surroundings.3,20
General movements, which are present from either preterm or term birth until 6 to 9 weeks of PTA, are characterized by variability, fluency, and complexity.3,20 A
lack of these features, i.e. the movements appear monotonous and jerky, implies abnormality. Three types of abnormal GMs are distinguished: poor repertoire, cramped-synchronized, and chaotic. Initially, in preterm-born infants, GMs are often identified as poor repertoire GMs. This type of movement may either normalize before or around term-equivalent age, or it remains persistently abnormal.21,22 They may also
evolve into cramped-synchronized GMs. The presence of cramped-synchronized GMs indicates an increased risk of developing CP.23 Before term age is reached,
GMs are referred to as preterm GMs. From term-equivalent until 6 weeks of PTA they are called writhing GMs. Detailed characteristics of GMs, for example, speed, amplitude, intensity, and the amount of space used can be assigned a score, resulting in a quantitative general movement optimality score (GMOS).24
At a PTA of 6 to 9 weeks the writhing movements fade out. From that same age, or perhaps as early as 4 weeks of PTA, FMs emerge.25 They follow a developmental
course and their occurrence peaks between 12 and 16 weeks of PTA. After this age they become discontinuous and have eventually faded out by 20 weeks of PTA. Fidgety movements are characterized by small, fluent, and circular movements with moderate speed and small amplitude, and they can involve all joints.23 These
dance-like movements are normal, but aberrant when the FMs are absent or greatly exaggerated in terms of speed, amplitude, and jerkiness. In case of the latter, the dance-like feature is lost, and the movements resemble those of a ‘puppet-on-a-string’. Both the absence of FMs and abnormal FMs - together referred to as aberrant FMs - imply an impaired neurological status. Along with FMs, a concurrent repertoire
of spontaneous movements and the first voluntary movements can be identified. This repertoire consists of various movement and postural patterns, including for example, swipes, hand-to-hand contact, and various finger postures. A scoring sheet, which results in a motor optimality score (MOS) was developed.3,4,6 The MOS consists of the
following quantitative and qualitative subscales: FMs, observed movement patterns, age-adequate movement repertoire, observed postural patterns, and movement character.6
Over the years, the method of assessing the early motor repertoire has improved and these advances should be regarded as an on-going process. By implementing scoring sheets for spontaneous movements, ranging from preterm until 20 weeks of PTA, both qualitative and quantitative measures have become available. Despite these advances, reference data for the early motor repertoire of two important groups of infants are still lacking, i.e. very preterm infants who are at risk of poor neurodevelopment and term infants who seldom run the risk of developing neurodevelopmental disorders.
Predictive value of the early motor repertoire for neurodevelopment
Motor development
To date, predicting neurodevelopment by assessing infants’ early motor repertoire focused mainly on preterm infants and their motor outcomes. It is known that these individuals have an increased risk of developing motor problems, i.e. CP, minor neurological dysfunction, or more subtle motor problems.26
The early motor repertoire has proven to be a reliable early marker for predicting CP in at-risk infants. The presence of both cramped-synchronized writhing GMs and the absence of FMs are strong indicators of the development of CP.23 They
have a sensitivity and specificity for predicting CP of approximately 98% and 91%, respectively.27–29 If the assessment of GMs is combined with cerebral imaging, the
predictive value increases even further.16,27,28,30–32 Recently, the added value of the MOS
and its subscales, which represent the early motor repertoire at around 3 months of PTA, increased on account of the fact that they were also found to be predictive of the development of CP.6,33
Interestingly, aspects of the early motor repertoire are not associated with the development of CP only, but also with that of minor neurological dysfunctions. In particular, aberrant FMs and abnormal movement character are indicative of the diagnosis of either CP or minor neurological dysfunction at school age.34
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Motor performance in general, i.e. not necessarily CP or minor neurological dysfunction, is also associated with the early motor repertoire. Spittle et al. for example, found that the quality of GMs and FMs is associated with the motor outcomes of very preterm-born children at 2 and 4 years of age.35 Furthermore, the
presence of abnormal FMs in infancy has been related to fine manipulative disabilities in adolescence.36 As yet, however, little information is available on the value of
assessing the early motor repertoire for predicting subtle differences in the motor outcomes of preterm-born children at school age.
Development of intelligence, cognition, and language
The assessment of the early motor repertoire is increasingly used to identify infants with an increased risk of poor development on the domains of intelligence, cognition, and language. Similar to predicting motor outcomes, the early motor repertoire of preterm-born infants is also used to predict outcomes on intelligence, cognition, and language skills. It is relevant to note that very preterm-born children run a three times higher risk of developing an intellectual impairment.37,38 In comparison to
term-born peers, the IQ scores of children term-born at less than 32 weeks of gestation are approximately 13 points lower.39 This difference in level of intelligence is inversely
related to the infants’ gestational ages at birth.40,41 Furthermore, attention and
other cognitive abilities, including memory and executive function, are also often compromised.37,42,43
Spittle et al. demonstrated that the quality of writhing GMs and FMs are not only predictive of motor outcome, but also of cognition at the ages of 2 and 4 years.35
Other studies reported that the early motor repertoire around 12 weeks of PTA, the quality of the movement character, and the quantity and type of postural patterns are important in predicting cognitive outcome up to 10 years of age.5,44–46 Whether
the aforementioned associations persist into young adulthood is unknown.
Intelligence, cognition, and language have not been studied in preterm infants only. Hitzert et al. reported that in typically developing infants detailed aspects of the early motor repertoire are associated with cognition at school age.47
Application of the early motor repertoire in various groups of high-risk
infants
The assessment of the early motor repertoire is most often applied in preterm-born infants. There are, however, many other groups of children at risk of poor development. Children who contracted an intrauterine infection have an increased risk
of poor neurodevelopment.48 Einspieler et al. used the assessment of the early motor
repertoire in infants born to mothers who had contracted a Zika virus infection during pregnancy. They found that the quality of FMs and the MOS predict neurological outcome. For the quality of FMs alone, a sensitivity and specificity of 70% and 95%, respectively, and an accuracy of 91% were found for poor neurological outcomes.49
These findings could probably be applied in the prediction of outcomes following similar intrauterine infections.
Another vulnerable group consists of children who are diagnosed with an inherited metabolic disease of the intoxication type (IMD-IT).50 On account of the accumulation
of toxic metabolites in such diseases these children also have an increased risk of poor neurodevelopment. Nevertheless, little is known about predicting these children’s outcomes. Bruggink et al. reported that in five infants with various types of inherited metabolic diseases, the assessment of the early motor repertoire seems to be useful for predicting neurodevelopment.51 Further research is needed to identify the early
motor repertoire and its associations with neurodevelopment in this group of infants.
Conclusion
The assessment of the early motor repertoire is an important method for the timely prediction of neurodevelopment. The aforementioned findings indicate that it deserves a more prominent place in infants’ daily clinical care, particularly in case of infants who run a high risk of developmental problems later on. Further exploration is required of the method’s diagnostic and prognostic value in various groups of infants.
Aims and outline of this thesis
The aim of this thesis is to address the characteristics of the early motor repertoire, its importance for the association with, and prediction of, various cognitive domains over a wide range of ages. Finally, to determine the clinical value of assessing the early motor repertoire of infants with rare diseases whose GMs have hardly been studied before. To study these aims the thesis consists of the following parts:
Part I. The characteristics of the early motor repertoire
Despite its frequent use, reference data on the qualitative and quantitative aspects of the early motor repertoire in preterm and term-born infants are lacking. In Chapter 2 we provide a description and comparison of the MOS of both groups.
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Part II. The predictive value of the early motor repertoire for neurodevelopment In Chapter 3 we report on the associations between the early motor repertoire in infancy and neurodevelopment at school age in very preterm-born children. In Chapters 4 and 5 we elaborate on the predictive value of the early motor repertoire for intelligence and cognition in preterm-born young adults. Additionally, in Chapter 6 we present a study on the early motor repertoire of term-born, healthy children in association with their language performance throughout childhood.
Part III. Exploring the scope of the assessment of the early motor repertoire
In Chapter 7 we present a case of an intrauterine infection with a human parechovirus that resulted in poor neurodevelopment, which was already manifest in the infant’s early motor repertoire. Furthermore, in Chapter 8 we explore the scope of the assessment of the early motor repertoire by studying the spontaneous movements of infants with IMD-IT.
In Chapter 9 we discuss our findings in relation to the existing literature and propose future perspectives. A summary of the thesis is provided in Chapter 10.
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Part I
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