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University of Groningen
The prevalence and severity of disease-related disabilities and their impact on quality of life in
neuromuscular diseases
Bos, Isaac; Wynia, Klaske; Almansa, Josué; Drost, Gerrie; Kremer, Hubertus; Kuks, Jan B. M.
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Disability and Rehabilitation
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10.1080/09638288.2018.1446188
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The prevalence and severity of disease-related
disabilities and their impact on quality of life in
neuromuscular diseases
Isaac Bos, Klaske Wynia, Josué Almansa, Gea Drost, Berry Kremer & Jan Kuks
To cite this article: Isaac Bos, Klaske Wynia, Josué Almansa, Gea Drost, Berry Kremer
& Jan Kuks (2018): The prevalence and severity of disease-related disabilities and their
impact on quality of life in neuromuscular diseases, Disability and Rehabilitation, DOI:
10.1080/09638288.2018.1446188
To link to this article: https://doi.org/10.1080/09638288.2018.1446188
© 2018 The Author(s). Published by Informa
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ORIGINAL ARTICLE
The prevalence and severity of disease-related disabilities and their impact on
quality of life in neuromuscular diseases
Isaac Bos
a
, Klaske Wynia
a,b
, Josu
e Almansa
b
, Gea Drost
a
, Berry Kremer
a
and Jan Kuks
a
a
Department of Neurology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands;
b
Department of
Community and Occupational Health, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
ABSTRACT
Purpose: People with neuromuscular disease experience lower quality of life levels than people from the
general population. We examined the prevalence and severity of a broad range of neuromuscular disease-
related disabilities and their impact on health-related quality of life.
Materials and methods: A cross-sectional postal survey study was conducted among patients diagnosed
with neuromuscular disease. Patients completed the Neuromuscular Disease Impact Profile, a disease-
related disability impact questionnaire, and two generic health-related quality of life questionnaires: the
medical outcome study Short Form Questionnaire and the World Health Organization Quality of Life-bref.
The impact of disabilities on quality of life was estimated using multiple regression analyses.
Results: Six hundred sixty two patients (68% response rate) completed the questionnaires. There were no
differences in quality of life between diagnosis-based subgroups. ‘Impairments in muscle functions’had
the highest prevalence and severity scores in the total sample and diagnosis-based subgroups.
Neuromuscular disease-related disabilities showed strong and independent associations with all aspects of
health-related quality of life. ‘Impairments in mental functions and pain’was the most important predictor
of health-related quality of life followed by ‘restrictions in participation in life situations’.
Conclusions: Although ‘impairment in muscle functions’is the most prevalent and severe disability, the
‘impairments in mental functions and pain’have a strong association with health-related quality of life in
patients with a neuromuscular disease.
äIMPLICATIONS FOR REHABILITATION
Disease-related disabilities have a strong and independent associations with all aspects of health-
related quality of life.
Although health-related domains of quality of life are affected by the neuromuscular disease, the
general quality of life is quite good.
The most prevalent and severe disability in total group and diagnosis-based subgroups is
‘impairments in muscle functions’.
The most significant predictor in health-related quality of life is ‘impairments in mental functions
and pain’.
ARTICLE HISTORY
Received 11 October 2017
Revised 22 February 2018
Accepted 24 February 2018
KEYWORDS
Neuromuscular disease;
Neuromuscular Disease
Impact Profile; disability;
health-related quality of life
Introduction
Neuromuscular diseases (NMDs) can be caused by dysfunction of
the anterior horn cell or sensory ganglion cell (neuronopathy),
peripheral nerve (neuropathy), neuromuscular junction (myasthe-
nia), or muscle (myopathy) [1]. Common impairments in function-
ing as a consequence of neuromuscular diseases include muscle
weakness, impairment in muscle endurance, involuntary muscle
activity (stiffness, myotonia, cramp and fasciculation), sensory loss,
autonomic dysfunction and impairment in the control of voluntary
movements [1]. These impairments cause fatigue and pain in
most people, which has a profound impact on their daily activities
and participation in life situations [1–5].
Quality of Life (QoL) has become increasingly important
in evaluating healthcare outcomes in recent decades.
Commonly, general quality of life is the perceived quality of an
individual’s daily life, including physical, psychological, social and
environmental aspects of the individual’s life [6,7]. In healthcare,
health-related quality of life (HRQoL) is the perceived quality of
life when affected by a disease or disabilities [8]. Several studies
found that all QoL domains were worse in NMD-groups compared
to healthy people in the general population [5], which can be
explained by NMD-related health problems such as poorer phys-
ical [5,9] and social functioning [10,11], pain [12–14], fatigue [15],
cognitive impairments and impaired emotional functioning [16].
Although these studies have generated clinically important
information, they are limited by their typical focus on the impact
of individual disabilities on HRQoL. Little is known of the relative
impact of aggregated NMD-related disabilities on HRQoL. Insight
CONTACT Isaac Bos i.bos@umcg.nl Department of Neurology, University Medical Center Groningen (UMCG), University of Groningen, P.O. Box 30001, 9700
RB, Groningen, The Netherlands
Supplemental data for this article can be accessed here.
ß2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/),
which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
DISABILITY AND REHABILITATION, 2018
https://doi.org/10.1080/09638288.2018.1446188
into this could facilitate our understanding of the impact of dis-
ease-related disabilities in NMDs on HRQoL.
The aim of this study is therefore to examine the prevalence
and severity of a large number of disease-related disabilities and
their impact on HRQoL in a sample of patients diagnosed with a
wide range of NMDs.
Methods
Sample and procedure
A cross-sectional postal survey was conducted among patients
diagnosed with an NMD and registered at the Department of
Neurology, University Medical Center Groningen, The Netherlands.
The inclusion criteria in addition to an NMD diagnosis were: being
aged 18 or older, and being able to read and write in Dutch.
A total of 980 eligible patients diagnosed with a neuromuscu-
lar disease were selected from the hospital patient record system.
To avoid inappropriately sending questionnaires, we crosschecked
for deceased patients using the national population register.
Patients received information about the study and were invited
to participate. Respondents completed the Neuromuscular Disease
Impact Profile (NMDIP), two generic health-related QoL question-
naires and some demographic and disease-specific questions.
Reminders were sent after two weeks if there was no response.
Measurement instruments
Disease-related disabilities were assessed using the NMDIP [1].
This measurement instrument is based on the International
Classification of Functioning, Disability and Health (ICF) [17] and
consists of 36 items covering four ICF components. Its items are
grouped into eight scales with four additional items. For the body
functions and participation component items, scoring options
ranged from 0 (no disability) to 4 (complete disability); for the
activities component items, scoring options ranged from 0 (no dis-
ability) to 3 (complete disability); and for the environmental fac-
tors component items, scoring options ranged from 0
(no support) to 2 (full support). Scores are summed for each scale.
To make the scores for each scale and the individual items com-
parable, the summed and individual scores were divided by the
highest possible score and multiplied by 100 to obtain a result
between 0 and 100. We established in previous work that the
NMDIP shows satisfactory levels of internal consistency:
Cronbach’s alphas ranged from 0.63 to 0.92, while mean inter-
item correlations ranged from 0.38 to 0.77 [1]. Test-retest reliabil-
ity was good: intraclass correlations ranged from 0.79 to 0.97 [18].
HRQoL was assessed using two generic HRQoL measurement
instruments, the Medical Outcome Study 36-item Short Form
Health Survey (SF-36) [19] and the World Health Organization
Quality of Life (abbreviated version) (WHOQoL-bref) [20]. The SF-
36 consists of eight scales and two separate questions covering
physical, psychological, and social aspects of health. Item scores
were coded, summed, and transformed to a scale ranging from 0
(worst QoL) to 100 (best QoL) for each dimension. The Cronbach’s
alpha for a recent NMD study ranged from 0.77 to 0.94 [1]. The
WHOQoL-bref consists of 26 items divided into four domains cov-
ering physical, psychological, social and environmental aspects
and has two single-item questions. For each scale, item scores
were coded, summed, and transformed to a scale ranging from 0
(worst QoL) to 100 (best QoL). The Cronbach’s alpha for a recent
study of NMD patients ranged from 0.60 to 0.84 [1]. Contextual
variables were assessed using three questions with a visual ana-
logue scale: General health status was assessed using the
EuroQol-visual analogue scale for the single question ‘How good
or bad is your health today?’[21], with the endpoints ‘Best
imaginable health state’scoring 100, and ‘Worst imaginable health
state’scoring 0. The extent of limitations was assessed using the
single question ‘To what extent are you limited due to your
NMD?’Response options are on a 10-point scale ranging from 1
(not limited at all) to 10 (completely limited). And general QoL
was assessed using the single question ‘How do you rate your
QoL?’, with the endpoints ‘Best imaginable QoL’scoring 10, and
‘Worst imaginable QoL’scoring 0.
Diagnosis-based subgroups
To examine the differences in the prevalence and severity of dis-
abilities between the relevant NMD subgroup we used the cat-
egorisation according to Rowland [22]: motor-neuron disorders,
muscle disorders, junction disorders, and peripheral nerve disor-
ders. Furthermore, the peripheral nerve disorders group was split
into primary motor and primary sensor subgroups because of the
differences in onset and expected differences in prevalence and
disability severity.
Data analyses
Descriptive statistics were used to examine the patient characteris-
tics. The prevalence of disabilities was calculated as the percent-
age of the patients who experience a disability (score >0). Severity
scores were calculated as the mean score of the disability
scores of all patients. To assess differences between diagnosis-
based subgroups, analysis of variance and T-tests were performed
for normally distributed continuous variables, a Chi-square test
for categorical variables, and a Mann–Whitney U-test and
Kruskal–Wallis test for not normally distributed variables.
The impact of the disease-related disabilities on HRQoL was
assessed using a series of multiple regression analyses with each
of the HRQoL variables as dependent variable. We first analysed
the impact of patient characteristics (age, gender, years since
diagnosis, employment status, and educational level) on HRQoL in
Model 1 to control for patient characteristics. We then analysed
the impact of the disease-related disabilities overall in Model 2.
Before being entered into the regression analysis, the ordinal and
categorical variables –gender, educational level and employment
status –were dichotomized. The expected direction of standar-
dized sz weights is negative, meaning that less disability equates
to better HRQoL. Special attention was given to examining the
multicollinearity between variables [23].
Statistical analyses were performed using the SPSS 23.0 soft-
ware package, SPSS Inc. Chicago, IL 60606-6307.
Results
Patient characteristics
Of the 980 eligible patients, 662 participants completed the ques-
tionnaires (68% response rate). The distribution of NMD diagnoses
across the various NMD subgroups is described in Supplementary
Table S1. Non-respondents did not differ from respondents in
terms of gender, but were younger than respondents (mean
age =53, SD ¼19.4).
The mean age of respondents was 59 years and their mean dis-
ease duration was 11 years (Table 1). Most respondents were mar-
ried or in a relationship, were of low education level and were
retired. All NMD-subgroups had similar levels of general QoL.
2 I. BOS ET AL.
Prevalence and severity of disease-related disabilities
The most prevalent disability reported in the total sample (Table 2)
was ‘impairments in muscle functions’, followed by ‘limitations in
activities of moving around’and ‘impairments in mental functions
and pain’. The peripheral nerve disorders subgroup, primary
sensor group, had the highest prevalence for ‘impairments in
mental functions and pain’and for ‘impairments in excretion
and reproductive functions’compared to the other disorders.
The most severe disability in the total sample was ‘impairments
in muscle functions’followed by ‘lack of support from social
security services’and ‘health services’, and ‘limitations in activ-
ities of moving around’. Disability severity differed statistically
significantly for most disabilities between NMD subgroups.
Impact of disease-related disabilities on QoL
We obtained satisfactory results, and there was no multicollinear-
ity: the variance inflation factor (VIF) for ‘activities of moving
around’was 5.6 and the average VIF was 2.0. The mean tolerance
was 0.59 and the range was from 0.20 to 0.85 and was never
below the critical value of 0.2.
Disease-related disability variables contributed significantly and
considerably to an important segment of the variance for all SF-36
and WHOQoL-bref domains. The significant standardized b
weights were in the expected direction, meaning that patients
who reported more disability experienced less QoL. The low sig-
nificant positive direction of the bweight for the variable ‘seeing
functions’in relation to the SF-36 variable bodily pain was some-
what unexpected.
The disabilities which were strong predictors for QoL evaluated
using the SF-36 (Table 3) were:
‘Impairments in mental functions and pain’(impairments
in sleep functions, fatigue, emotional functions, thought
functions, and sensation of pain) was a significant pre-
dictor for six out of eight QoL variables.
‘Impairments in muscle functions’(impairments in muscle
power functions and muscle endurance functions) and
‘limitations in activities of moving around’(limitations in
changing body position, maintaining body position,
transferring oneself, walking, using transportation, and
recreation and leisure) were important predictors in the
‘physical functioning’QoL domain.
‘Restrictions in participation in life situations’(restrictions
in mobility, relationships and recreation and leisure) was
an important predictor in the ‘role physical’and ‘social
functioning’QoL domains.
‘Limitations in self-care and domestic activities’(limitations
in fine hand use, hand and arm use, washing oneself, car-
ing for body parts, going to the toilet, dressing, preparing
meals, and doing housework) and ‘restrictions in mental
functions and pain’were important predictors in the ‘role
emotional’QoL domain.
The disabilities which were strong predictors for QoL evaluated
using the WHOQoL-bref (Table 4) were:
‘Restrictions in participation in life situations’was a signifi-
cant predictor for three out of four QoL variables.
‘Impairments in mental functions and pain’was an import-
ant predictor in the ‘physical health’and ‘psychological
health’QoL domains.
‘Impairments in excretion and reproductive functions’
(impairments in defecation functions, urination functions,
and sexual functions) was an important predictor in the
‘social relations’QoL domain.
‘Lack of support from immediate family’and ‘lack of sup-
port from social security services’showed significant con-
tributions in the ‘social relationships’QoL domain
‘Lack of support from immediate family’showed a signifi-
cant contribution in the ‘environment’QoL domain.
Discussion
This study examined the prevalence, severity and impact of a
broad range of disease-related disabilities on HRQoL in a large
sample of NMD patients. The study’s most important finding is
that disease-related disabilities have a strong and independent
association with all aspects of HRQoL. Although ‘impairments in
muscle functions’was the most severe disability with the highest
prevalence in all diagnosis-based subgroups, the ‘impairments in
Table 1. Sample characteristics for the total sample (n¼662) and subgroups.
Total
sample
(n¼662)
Motor-neuron
disorders
(n¼62)
Muscle
disorders
(n¼155)
Junction
disorders
(n¼177)
Peripheral
nerve disorders
primary motor
(n¼71)
Peripheral
nerve disorders
primary sensor
(n¼197)
Gender n(%)
Female 335 (51) 31 (50) 77 (50) 115 (65) 32 (45) 80 (41)
Age (years)
Mean (SD) 59 (15.4) 60.8 (12.7) 51.6 (16.8) 58.7 (15.7) 55.7 (14.4) 65.3 (12.3)
Range 19–92 29–86 19–92 22–89 26–82 32–91
Relationship status n(%)
Married/partnership 468 (71) 51 (82) 95 (61) 128 (72) 52 (73) 142 (72)
Unmarried/widowed/divorced 193 (29) 11 (18) 60 (39) 48 (27) 19 (27) 55 (28)
Educational level n(%)
Lower level 480 (73) 41 (66) 114 (75) 131 (74) 51 (73) 143 (73)
Higher level 177 (27) 21 (34) 37 (25) 46 (26) 19 (27) 54 (27)
Employment status n(%)
Employment 187 (28) 18 (29) 46 (30) 60 (34) 21 (30) 42 (21)
Unemployment 475 (72) 44 (71) 109 (70) 117 (66) 50 (70) 155 (79)
Range 0–65 1–64 1–62 0–65 0–55 0–61
Health-state
EQ-VAS, median (IQR) 67 (30) 65 (23) 65 (25) 70 (25) 70 (30) 65 (30)
Extent of limitations
Median (IQR) 5 (4) 7 (3) 6 (5) 5 (3) 6 (4) 6 (5)
Quality of Life
QoL-rate, median (IQR) 7 (2) 7 (2) 7 (2) 7 (2) 7 (1) 7 (2)
IQR: Inter quartile range.
THE IMPACT OF NEUROMUSCULAR DISEASES ON QOL 3
mental functions and pain’was the most important predictor of
HRQoL, followed by ‘restrictions in participation in life situations’.
Our finding that ‘impairments in mental functions and pain’
was an important predictor for QoL confirms previous studies
[4,24]. The same applies to ‘restrictions in participation in life sit-
uations’[10,11].
Our finding that the most prevalent and severe disability
‘impairments in muscle functions’was not a strong predictor for
HRQoL is also interesting. In contrast, the strongest predictor,
‘Impairment in Mental Functions and Pain’that yielded relatively
little impairment. Other studies also reported this phenomenon
[5,25,26]. This phenomenon stands for a counter-intuitive preser-
vation of QoL in chronic illness and disability called the ‘disability
paradox’, a theory that tries to explain why people with serious
and persistent disabilities report good quality of life [5,25]. We
found no differences in general QoL between diagnosis-based
subgroups, which indicates the relatively minor contribution that
medical diagnosis make to predicting HRQoL. The relative high
score for general QoL is an example of the ‘disability paradox’.
We found that disease-related disabilities are important indica-
tors of HRQoL. These findings underline the importance of atten-
tion to the broad spectrum of consequences of NMDs.
The positive association of increased ‘impairments in seeing
functions’with perceived QoL in the ‘bodily pain’domain (SF-36),
which means that worsening sight has a relatively small but a
positive association with a patient’s experienced pain, was an
unexpected finding. Given the number of relationships under
investigation, this could be a chance finding, but on the other
hand, worsening sight could cause a decrease in activity and
thereby a decrease in experienced activity-related muscle pain. A
comparable unexpected finding is the relatively small positive
association of increased ‘impairments in movement functions’
with quality of environmental aspects (WHOQoL-bref). This can
probably be explained by the beneficial effects of adaptations in
the environment and the use of assist devices such as mobil-
ity scooters.
We also found that the association of disabilities with HRQoL
was dependent on the HRQoL measurement instrument used. For
example, when using the WHOQoL-bref, we found that limitations
in activities did not affect one of the four domains of QoL.
However, when using the SF-36, these limitations did affect QoL
in the ‘physical functioning’and ‘role emotional’domains.
Conversely, we found that environmental aspects had no associ-
ation with HRQoL when using the SF-36, while ‘lack of support
from immediate family or social security services’affected one or
two of the four WHOQoL-bref domains. This finding indicates that
HRQoL continues to be an evolving concept, which should be
borne in mind when choosing a QoL measurement instrument
and interpreting results.
We examined our expectation of differences in disability preva-
lence and severity between the peripheral nerve disorders sub-
groups. We found significant differences between ‘impairments in
mental functions and pain’and ‘impairments in excretion and
reproductive functions’. The prevalence and severity of
‘impairments in mental functioning and pain’, and ‘impairments in
reproductive functions’were higher in the primary sensor group,
probably because the autonomous nervous system is more
involved compared to the motor sensory group.
We did not expect a prevalence of more than 50% for
‘impairments of swallowing and speech functions’in our muscle
group, but it should be realized that swallowing is a complex pro-
cess not only comprising pharyngeal sphincters but also facial, lin-
gual, and chewing muscles. Self-evidently swallowing is an
important factor for patients’prognosis and QOL [27,28].
Table 2. Prevalence and severity of disease-related disabilities in the total sample and in disease subgroups.
Total sample
(n¼662)
Motor-neuron
disorders (n¼62)
Muscle disorders
(n¼155)
Junction disorders
(n¼177)
Peripheral nerve
disorders primary
motor (n¼71)
Peripheral nerve
disorders primary
sensor (n¼197)
Subgroup
differences#
% mean (CI) SD % mean (CI) SD % mean (CI) SD % mean (CI) SD % mean (CI) SD % mean (CI) SD Chi-Square p
Impairments in …
Muscle functions 94 44.8 (43.0–46.6) 23.0 98 58.7 (52.3–65.0) 25.0 99 52.4 (48.9–55.9) 21.8 93 35.3 (32.3–38.2) 19.1 93 44.3 (39.0-49.6) 22.2 91 42.3 (38.9–45.6) 22.5 66.8 <0.001
Movement functions 70 22.0 (20.5–23.4) 17.7 76 33.5 (27.7–39.3) 20.5 69 21.5 (18.4–24.6) 17.6 58 13.6 (11.4–15.7) 13.3 86 23.4 (19.2–27.5) 16.7 91 25.9 (23.2–28.6) 17.5 66.7 <0.001
Excretion and reproductive functions 47 15.9 (14.3–17.4) 17.2 53 16.1 (10.7–21.5) 18.1 43 15.8 (12.7–19.0) 16.6 48 14.0 (11.5–16.5) 14.2 51 12.3 (27.7–39.3) 17.8 67 18.8 (15.6–22.0) 19.2 7.3 0.119
Swallowing and speech functions 38 9.3 (21.4–23.9) 15.1 37 13.8 (7.7–19.8) 23.4 51 14.0 (11.2–16.7) 16.8 50 11.5 (9.5–13.4) 13.0 19 4.0 (1.6–6.5) 10.0 26 4.4 (3.2–5.6) 8.4 59.1 <0.001
Mental Functions and Pain 79 22.6 (21.4–23.9) 15.1 87 21.5 (17.7–25.3) 14.4 80 24.3 (21.5–27.1) 16.1 79 21.2 (18.9–23.5) 14.4 89 18.3 (14.8–21.8) 13.7 95 24.7 (22.3–27.1) 15.4 10.5 0.033
Seeing functions 40 15.3 (13.7–17.0) 20.8 21 5.7 (2.8–8.7) 11.5 37 14.4 (11.0–17.8) 20.8 68 26.2 (22.8–29.5) 22.5 20 7.2 (2.9–11.5) 17.4 34 11.8 (9.1–14.5) 18.3 86.4 <0.001
Limitations in …
Activities of Moving Around 86 30.6 (28.5–32.7) 27.4 98 48.8 (40.5–57.1) 32.7 95 41.3 (36.6–45.9) 29.3 73 16.4 (13.7–19.1) 18.0 83 28.9 (23.1–34.7) 24.5 88 29.9 (26.4–33.5) 25.4 99.2 <0.001
Self-care and Domestic Activities 76 21.8 (19.8–23.8) 26.5 98 48.0 (38.7–57.1) 36.2 86 31.0 (26.1–35.8) 30.5 68 11.7 (9.4–14.0) 15.5 75 17.3 (12.7–21.9) 19.4 70 17.3 (14.2–20.4) 22.1 85.6 <0.001
Restrictions in …
Participation in Life Situations 52 15.1 (19.8–23.9) 26.5 63 25.3 (18.3–32.2) 27.0 65 20.7 (17.0–24.3) 22.8 39 9.3 (6.9–11.8) 16.4 49 11.7 (7.4–15.9) 17.8 53 13.9 (11.3–16.6) 19.0 40.2 <0.001
Lack of support from …
Immediate family 35 23.8 (21.1–26.5) 35.1 27 16.1 (8.9–23.3) 28.3 37 24.8 (19.2–30.5) 35.8 34 21.2 (16.4–26.0) 32.2 32 21.1 (13.2–29.0) 33.4 39 28.8 (23.2–34.3) 39.1 5.9 0.204
Social security services 21 35.5 (30.9–40.1) 38.2 20 28.6 (14.2–43.0) 37.1 28 36.4 (28.0–44.7) 36.8 18 33.6 (24.1–43.0) 37.9 57 42.9 (28.3–57.4) 42.3 52 35.3 (25.2–45.5) 38.6 2.3 0.686
Health services 48 32.0 (30.9–40.1) 36.7 55 33.9 (25.0–42.7) 34.8 52 34.6 (28.8–40.5) 36.9 42 28.2 (22.8–33.7) 36.4 39 26.1 (17.6–34.5) 35.7 52 34.9 (29.5–40.3) 37.7 6.8 0.145
%Prevalence, severity (mean disability) score: score 0: no disability; score 100: complete disability. ‘Lack of support’score 0: no support, score 100: full support.
#Independent Kruskal–Wallis test; CI: confidence interval.
4 I. BOS ET AL.
Our study has some important strengths. First is the fact that
we examined the impact on HRQoL of a broad range of disease-
related disabilities, separately and in relation to each other, while
most studies examined only one or some disabilities in one or
some NMDs. As a result, this study offers a unique insight into the
consequences of NMD. Second, this study examined the conse-
quences of a large sample of NMDs representing all acknowl-
edged diagnosis-based subgroups and not just one disease or a
few diseases as is usually the case. Combined with our finding
that it is the disease-related disabilities rather than the medical
diagnosis, which are relevant to predicting HRQoL, our findings
are relevant to a broad population and could have important
implications for the treatment of patients with chronic diseases
such as NMD. Insight into the prevalence, severity and relative
impact of a large number of disease-related disabilities could con-
tribute to medical and non-medical support of NMD patients.
Furthermore, if the focus of support is shifted from medical diag-
noses to disabilities, the professionals who support patients with a
Table 3. Impact of disease-related disabilities on the SF-36 QoL variables.
SF-36
Physical
functioning
ß
Role
Physical
ß
Bodily
pain
ß
Vitality
ß
Social
functioning
ß
Role
emotional
ß
Mental
health
ß
General
health
ß
NMDIP
Impairments in ….
Muscle functions –0.20 –0.06 0.12 –0.14 –0.07 0.21 –0.02 –0.08
Movement functions 0.09 –0.01 –0.06 0.14 –0.06 –0.02 –0.10 –0.10
Excretion and reproduc-
tive functions
–0.00 –0.11 0.04 –0.04 –0.11 –0.06 0.11 –0.14
Swallowing and speech functions 0.04 –0.01 –0.10 –0.11 0.11 0.08 –0.13 –0.02
Mental functions and pain –0.08 –0.16 –0.59
–0.53
–0.36
–0.40
–0.34
–0.36
Seeing functions 0.09 –0.00 0.110.09 –0.09 –0.02 –0.00 –0.01
Limitations in ….
Activities of moving around –0.57 0.20 –0.08 0.02 0.24 0.29 0.15 0.19
Self-care and domestic activities –0.11 0.15 –0.04 0.13 –0.17 –0.42 –0.03 –0.10
Restrictions in ….
Participation in life situations –0.10 –0.46 –0.09 –0.08 –0.32 –0.07 –0.12 –0.15
Lack of support from ….
Immediate family 0.04 0.04 0.02 0.04 0.01 0.01 0.13 0.03
Social security services –0.06 0.00 –0.05 –0.02 0.05 –0.12 –0.03 0.03
Health services 0.02 0.03 –0.05 –0.01 –0.07 0.04 –0.01 0.01
R
2
0.73 0.31 0.52 0.51 0.49 0.27 0.29 0.43
DR
2
# 0.66 0.22 0.41 0.33 0.38 0.19 0.24 0.31
F 20.7 3.5 8.35 7.92 7.33 2.92 3.23 5.83
F Change# 26.78 3.47 9.35 7.26 8.01 2.91 3.69 5.91
¼p<0.05;
¼p<0.01;
¼p<0.001.
In bold: statistically significant sz values.
#¼compares Model 2 (disabilities) vs. Model 1 (patient characteristics).
Table 4. Impact of disease-related disabilities on the WHOQOL-bref QoL variables.
WHOQOL-bref
Physical health
ß
Psychological health
ß
Social relationships
ß
Environment
ß
NMDIP
Impairments in ….
Muscle functions –0.09 –0.03 0.02 –0.01
Movement functions 0.06 0.10 0.20 0.21
Excretion and reproductive functions –0.05 –0.13 –0.41 –0.03
Swallowing and speech functions –0.06 –0.05 0.14 –0.06
Mental functions and pain –0.54
–0.28–0.21 –0.21
Seeing functions 0.09 –0.11 –0.08 –0.05
Limitations in ….
Activities of moving around –0.04 0.19 0.00 –0.13
Self-care and domestic activities 0.07 –0.04 –0.13 –0.13
Restrictions in ….
Participation in life situations –0.21
–0.25–0.14 –0.27
Lack of support from ….
Immediate family 0.01 0.00 –0.20
–0.24
Social security services –0.12 –0.07 –0.21–0.07
Health services 0.09 –0.05 0.09 –0.07
R
2
0.70 0.30 0.38 0.43
DR
2
# 0.46 0.23 0.34 0.36
F 17.94 3.33 4.76 5.86
F Change# 16.60 3.58 5.99 6.86
¼p<0.05.
¼p<0.01.
¼p<0.001.
In bold: statistically significant sz values.
#¼compares Model 2 (disabilities) vs. Model 1 (patient characteristics).
THE IMPACT OF NEUROMUSCULAR DISEASES ON QOL 5
chronic disease might exchange knowledge and experiences, or
could integrate their activities. This ‘joining forces’could contrib-
ute to the QoL of the chronically ill.
Conclusions
Although impairment of muscle function is the most prevalent
and severe disability, impairment of mental function and pain
have a strong association with HRQoL of NMD patients.
Ethical approval
Ethical approval was obtained from the local ethics committee,
the Medical Ethical Committee of the University Medical Center
Groningen. Reference: METc 2009.310. Informed consent was
obtained from all participants.
Acknowledgements
We wish to thank the patients who participated in this study and
shared their personal information about the consequences of their
disease by taking the time to complete our questionnaires. We
thank the students who assisted in data collection: Ronald Brans,
Kyra van der Beek, Hanna Bosman, Annelies Verschure, Carolien
Verschure and Marieke Verschure. This study was supported
by the Neurology department of the University Medical
Center Groningen.
Disclosure statement
The authors report no declarations of interest.
This study received no funding. It was a piece of research con-
ducted as part of a doctoral degree.
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