Identifying premature infant at high and low risk for motor delays using motor performance testing and MRS
Patricia Coker-Bolt, PhD OTR/L, FAOTA1; Kathryn Hope2, MPH; Viswanathan Ramakrishnan, PhD3; Truman Brown, PhD4; Denise Mulvihill, MD1, and Dorothea Jenkins, MD2
1Division of Occupational Therapy, 2Department
of Pediatrics, 3Public Health Sciences, 4Radiology, Medical University of South Carolina, Charleston, SC
ABSTRACT
Background:
• Premature infants with normal cranial ultrasounds remain at risk for later
motor delays, which go undetected in early infancy.2
• Of the 12-16% of children with developmental delay, only half will be
identified by the time they enter kindergarten.1
• The Test of Infant Motor Performance (TIMP) is the current gold
standard infant motor assessment, but rarely used by pediatricians
during well-child visits due to lack of time and special training required.
• A short, standardized screening test administered to infants in the first
months of life would target early intervention to those most at risk.3
• In our previous work, Rasch partial credit model was used to analyze
and select 10 TIMP items with strongest correlation to motor ability at 12
months. New scales were then developed for more sensitive scoring of
these 10 items, comprising a novel screening tool, the Specific Test of
Early Infant Motor performance (STEP) (Figure 1).
Specific aims: Evaluate the robustness of a new, shortened, screening
assessment (STEP) through factor analysis of 10 motor items, and test the
STEP against current validated infant motor skills assessments and
outcome measures of development.
DESIGN/ METHODS
Design: A secondary analysis of an existing cohort of 22 preterm infants
(24-35 weeks gestation), with video recorded motor tests at 12 weeks and
12 months corrected gestational age (CGA). (Table 1)
Figure 1. Representative schematic of STEP scale for “Prone Extension”
Funded by MUSC’s SCTR Discovery & Early Career Grant FY13
UL1 TR000062
• The STEP is quick and easy to administer and score and requires
minimal training of health care professionals.
CONCURRENT AND EXTERNAL VALIDITY OF THE STEP
Figure 2. Correlations between the STEP and TIMP
• STEP correlated with TIMP scores at
term (r=0.062, p=0.003), 12 weeks CGA
(r=0.79, p<0.001), as well as the change
in TIMP scores from term to 12 weeks
(r=0.46, p=0.035), indicating it might be a
short, specific surrogate measure of a
much longer motor test. (Fig. 2)
Table 3 & Figure 3. Correlations of STEP and TIMP scales at 12-weeks
CGA to Bayley scores at 12-months
Gross
Motor
Bayley:
Fine
Motor
Total Motor
Score
EVALUATION OF ROBUSTNESS OF THE STEP
Table 1. Patient Demographics
Total Infants (N=22)
Sex
10 Females, 12 Males
Race
11 Caucasians, 11 African Americans
GA at Birth (mean ± SD)
29.6 ± 2.9 weeks
Birth weight (mean ± SD)
1259 ± 634 grams
Intracranial lesions
4 IVH (3 grade I, 1 grade II), 0 infarcts/PVL
Risk (TIMP at 12-weeks CGA)
9 High; 13 Low
Bayley Motor Outcome (N=19)
8 Average; 11 Low/Below Average
Pull to sit
Prone extension
Supine with no vision
Supine with vision
Standing
Supine sitting
Grasp
Kicking
Rolling with leg
% variance explained
Head Control
Upper
Extremity
Lower
Extremity
0.89540
0.89496
0.84610
0.76003
0.69165
0.76553
0.24003
0.38154
0.65745
68%
-0.23615
-0.15936
0.20399
-0.30853
-0.43411
0.36989
0.72577
0.48327
0.11327
20%
-0.06632
-0.21346
-0.16812
0.16172
0.23230
0.00095
-0.29594
0.76373
-0.17037
12%
• 1 item (rolling with arm) was unable to accurately be scored by viewing
existing video tapes, therefore the STEP score was constructed from 9
items for the EFA analysis.
• A pattern of relationships exists between STEP items that evaluate
head, arm, and leg movements (Table 2).
• STEP items related to head movements are likely influencing the overall
score (Table 2).
R value 0.68519 0.47682
p-value 0.0012
0.039
TIMP Scale:
R value 0.474
n/s
p-value
0.04
0.68634
0.0012
• Early motor skills should reflect biochemical evidence of subtle brain
injury. Preliminary analysis of the STEP scales showed correlations to
key brain metabolites.
• The STEP demonstrated good psychometric properties and predictive
abilities for infant developmental outcomes on the Bayley at 12
months.
• The motor items of STEP were grouped into three meaningful latent
constructs which show a pattern of relationships between motor
movements which evaluate head, arm, and leg movements.
• Quality of movement is a marker of the integrity of an infant’s nervous
system and could be a predictor of developmental disability and provide
valuable information on how at-risk infants interact with people and
objects in their environment.3,7
0.437
0.061
• STEP correlated better with Bayley outcomes than the TIMP (Table 3,
Figure 3)
Table 4. Motor test associations with common MRS metabolites in WM
• MRS metabolite ratios mI/Cr,
Metabolites
mI/NAA,
and
NAA/Cho
WM mI/Cr
showed the most significant
associations with the 12 week WM mI/NAA
TIMP and STEP scores WM NAA/Cho
(Table 4)
• The 10-item STEP at 12-weeks showed a much stronger correlation than
the concurrent full 42-item TIMP with the Bayley at 12-months.
• Early head movements, patterns of standing, kicking, and visual
responses may be sensitive to discriminate differences between typical
and at-risk infants.
STEP Scale:
Table 2. Latent constructs of STEP using Exploratory Factor Analysis (EFA)
Measures of Outcome:
• STEP scored from existing video recordings of TIMP at 12 weeks CGA.
• Test of Infant Motor Performance (TIMP) at term and 12 weeks CGA.
• Bayley III Scales of Infant and Toddler Development (Bayley III) at
12 months CGA. Bayley subscale scores ≤8 = low/below average 4,5.
• MRS: Siemens 3T: Single voxel [15 x 15 x 15 mm] in basal ganglia (BG)
and frontal lobe white matter (WM) [echo PRESS sequence128 avg,
TR=2000ms, TE 30ms, 270ms].
• Data Analysis: Pearson’s correlational coefficient was used to relate
TIMP, Bayley and STEP scores. Exploratory factor analysis (EFA) was
used to identify latent constructs of STEP. Logistic regression, using EFA
scores, was performed to predict dichotomized Bayley outcome.
Sensitivity and specificity of EFA STEP scores were evaluated using
predictive outcomes versus actual outcomes. A drop-one-predict
evaluation was used to assess external validity.
DISCUSSION
RESULTS
STEP
(p=)
0.008
0.016
0.006
TIMP
(p=)
0.007
0.026
0.0197
Table 5. Comparison of common infant tests and STEP:
Sensitivity and Specificity6
Assessment
Sensitivity
Specificity
STEP
TIMP
Cranial ultrasound
Neurologic Exam
0.75
0.86
0.70
0.88
0.82
0.68
0.69
0.87
• Ability of the STEP to predict Bayley Motor outcomes , using EFA scores,
in the current cohort: Sensitivity =1.0 and Specificity= 0.91
• Ability to prospectively identify at risk infants (External Validity):
Sensitivity=0.75 and Specificity=0.82 (Table 5).
CONCLUSIONS
• Though our numbers are small, the strength of the associations are
encouraging and provide strong pilot data and proof of concept for
potential validity of the STEP assessment.
• This is a preliminary analysis of the psychometric properties of the STEP.
Validation of the STEP as a clinically useful infant motor assessment
requires further analysis.
• Future work: currently enrolling and testing infants using a revised STEP
for adequate subject to variable ratio needed to complete a more through
factor analysis of the psychometric properties of the STEP.
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