1. University of Utah, Salt Lake City UT
Limits of Postural Stability in Myotonic Dystrophy Compared to Normative Values
Mary Pautler, MPH
University of Utah, Salt Lake City UT

2. Myotonic Dystrophy Type 1 (DM1)
Prevalence estimated at 1/8,000
Dominantly inherited, multisystem disorder
Characterization:
Progressive muscle weakness
Myotonia
Early onset cataracts
-Increased risk for falls
Limitations with mobility and gait impact quality of life
This is a preliminary look at postural stability in this population.
Myotonic dystrophy type 1 (DM1)
- most common adult onset muscular dystrophy,
- current prevalence estimated at 1 in 8,000.
Dominantly inherited disorder,
- caused by an unstable CTG repeat expansion in DMPK gene
Brief overview, DM1 is characterized by
- Progressive muscle weakness –
predominantly seen in distal muscle: finger flexors, ankle dorsiflexors
- Myotonia
- Early onset cataracts (<50 years of age)
This population has a 10-fold increased risk for falls.
Number of falls increase, as ankle dorsiflexor strength declines.
As reported by patients with DM1,
- the greatest impact on their QOL is limitations with mobility and gait.
Gait impairments and postural control have both been shown to be associated with muscle weakness.

3. Study Design Study Visits Inclusion Criteria Exclusion Criteria
Aim 1: Compare Limits of Stability via maximum excursion (MXE) scores for DM1 versus normative values.
Aim 2: Compare MXE scores at baseline and 3-months.
Study Visits
Baseline and 3-months
Inclusion Criteria
Age 18-60
Genetically confirmed DM1
Onset of symptoms after age 12
Exclusion Criteria
Mexiletine, Coumadin or other anticoagulants
Other neuromuscular disorder
Significant trauma within one month
We evaluated a subset of data from a longitudinal cohort study aimed to characterize
functional outcomes associated with disease progression in DM1.
I was specifically looked at:
#1) Comparing limits of stabiliyt between DM1 and normal values using max excursion scores.
#2) Compare max excursion at baseline and 3-months to evaluate changes over time.
Participants attended two visits; baseline and 3- months. All testing was completed at both visits.
Inclusion/exclusion were broad –
- participants between the ages of 18-60
- genetically confirmed DM1,
- symptom onset after age 12.
- Mexiletine use was exclusionary

4. Limits of Stability Maximum Excursion (MXE):
Voluntary maximum displacement of center of gravity while maintaining a fixed base of support.
Maximum Excursion (MXE):
Measure of maximum movement potential
Illustrates limits of stability
Reduced MXE values indicate:
Reduced limits of stability
Decreased stability during weight shifting
Increased fall risk
Postural control is necessary for safe and independent functioning.
Impairments in postural control are seen when stability limits are reduced.
LOS is the max distance one can voluntarily shift their weight,
while maintaining a fixed base of support, without stepping or falling –
this can be visualized as inverted cone surrounding an individual.
One measure of limits of stability is Maximum Excursion (MXE) –
this measures that distance one can lean their COG without a fall.
A reduction in max excursion indicate:
- limit of stability are constricted,
- decreased stability during movement
- And increased risk of falls
Limits of stability have NOT been described in individuals with DM1.
Balance and Posture, Andrew L. McDonough

5. Computerized Posturography
NeuroCom Balance Manager System
Anterior
We used the NeuroCom Balance System to quantify LOS.
- The participant is centered on a force place.
- Screen provided real time feedback on location and movement.
- Instructions to shift their weight towards targets without moving their feet or using walls for stabilization.
The figure shows output from one of our tests –
tracking lines illustrate the actual path traveled from the central starting point to each target.
Targets placed at theoretical limit of stability, determined by the patient’s age and height.
As shown in this figure, healthy individuals tend to reach, or surpass, the targets.
MXE score for this individual would take the average (CLICK) excursion achieved in each direction.
Compare this tracking report to one from a participant with DM1 (SLIDE 5)
- maximum distance achieved was substantially reduced.
Posterior
NeurCom Clinical Interpretation Guide, Computerized Dynamic Posturography

6. Limit of Stability Tracing DM1 participant
Anterior
Compare this tracking report to one from a participant with DM1 (SLIDE 5)
…. maximum distance achieved was substantially reduced.
Posterior

7. Participant Demographics
Total enrollment N=22
Withdrawal = 1
Data analysis based on N=21
Age, yrs [mean (range)]
40 (28-57)
Gender [N(%)]
9 (43%) Female
12 (57%) Male
Symptom Duration, yrs [mean (range)]
19 (2-31)
CTG Repeat Length [mean (range)]
433 ( )
For this study;
- 22 individuals were enrolled.
- 1 withdrew due to safety concerns not associated with the study procedures
- Analysis was completed on 21 subjects
Enrolled participants:
ranged in age year,
Average duration of symptoms is 19 years (range from 2 to 31).
CTG repeat lengths ranging from approx 180- almost 900.

8. Maximum Excursion (MXE): Comparison of DM1 to Normative Values
Results: Aim 1
Maximum Excursion (MXE): Comparison of DM1 to Normative Values
Age Cohort (yrs)
20-39
(n=11, gender 6M/5F)
40-59
(n=10, gender 6M/4F)
Mean MXE
Normal Value (% (SD))
96.2 (6.7)
98.0 (5.9)
DM1 (% (SD))
66.33 (12.63)
48.67 (12.83)
p-value
p<0.001
The MXE scores are reported as percent of theoretical limit.
stratified by age groups, 20-39yrs and 40-59yrs
MXE Results were compared to age-matched normal values.
Normal values were provided by researchers collaborating with NeuroCom.
121 controls make up the normal values listed for the two age groups.
RESULTS AIM1:
We comparing MXE between DM1 and normal values:
Found: MXE values were significantly reduced in DM1 for both age groups.
Figures below are visual representation of the max excursion achieved by the DM1 and normal groups.
Normal values are in red
DM1 values are in Blue

9. Maximum Excursion (MXE): Comparison of Baseline to 3-Month Visit
Results: Aim 2
Maximum Excursion (MXE): Comparison of Baseline to 3-Month Visit
Age Cohort (yrs)
Mean MXE
Baseline Visit (%)
3-Month Visit (%)
p-value
20-39
66.33
65.78
0.55
40-59
48.67
51.1
0.73
For Aim 2:
Compared Max excursion at baseline and 3-months, just among the DM1 group.
Unable to detect significant changes in scores between the two visits.
Three months may be too short a time period to detect a measurable change.

10. MXE vs DF Strength (r = 0.65, p=0.004)
Results
MXE vs Age (r = -0.64, p=0.004)
MXE vs DF Strength (r = 0.65, p=0.004)
#1) Based on our results, appears to be an overall age affect.
Comparing MXE to Age within the DM1 population:
- A moderate negative correlation.
- As DM1 individuals age, their max excursions are restricted.
We were interested in what additional factors may contribute to excursion values.
#2) We measured Max dorsiflexion strength using QMA –
- max strength showed moderate positive correlation with MXE.
#3) Finally - compared a common clinical test, modified dynamic Gait Index, to MXE.
The gait index tests dynamic balance in the presence of external demands.
Lower scores indicate decreased balance.
- We found a moderate positive correlated between gait index and MXE.
MXE vs mDGI (r = 0.60, p=0.008)

11. Summary
Limits of stability are significantly reduced in DM1 as compared to normal values.
No change in stability limits over 3-months.
Age, dorsiflexion strength and dynamic balance correlate with stability limits.
Evaluate additional contributing factors.
Consider limits of stability for measuring disease progression.
To summarize: We found:
- LOS to be significantly reduced in DM1 compared to normal values.
- no change in stability limits over 3 months,
- And age, dorsiflexion strength and dynamic balance to moderately correlate with limits of stability.
We know LOS is impacted, and this data suggests that age and dorsiflexion strength play a role –
One area to further explore is what other factors contribute to this decline in LOS?
(ankle ROM, plantarflexion strength)
A second direction - evaluate the utility of LOS as a measure of disease progression over a longer time frame.

12. CONTRIBUTORS / SUPPORT
Heather Hayes, PT, DPT, NCS, PhD Man Hung, PhD Jerry Bounsanga Yushan Gu Deanna DiBella, PT, MPT Evan Pucillo, PT, DPT Caren Trujillo, RN, MSN Missy Dixon, PhD, MS Russell Butterfield, MD, PhD Nicholas Johnson, MD

13. Horak, F. B. (2006). Postural orientation and equilibrium: what do we need to know about neural control of balance to prevent falls? Age Ageing, 35 Suppl 2, ii7-ii11