Journal of Neurology
https://doi.org/10.1007/s00415-022-11310-9
ORIGINAL COMMUNICATION
The epidemiology of dystonia: the Hannover epidemiology study
Dirk Dressler1 · Eckart Altenmüller2 · Ralf Giess3 · Joachim K. Krauss4 · Fereshte Adib Saberi5
Received: 18 May 2022 / Revised: 22 July 2022 / Accepted: 23 July 2022
© The Author(s) 2022
Abstract
The prevalence of dystonia has been studied since the 1980s. Due to different methodologies and due to varying degrees of
awareness, resulting figures have been extremely different. We wanted to determine the prevalence of dystonia according to
its current definition, using quality-approved registries and based on its relevance for patients, their therapy and the health
care system. We applied a service-based chart review design with the City of Hannover as reference area and a population
of 525,731. Barrier-free comprehensive dystonia treatment in few highly specialised centres for the last 30 years should have
generated maximal dystonia awareness, a minimum of unreported cases and a high degree of data homogeneity. Prevalence
[n/1mio] and relative frequency is 601.1 (100%) for all forms of dystonia, 251.1 (42%) for cervical dystonia, 87.5 (15%) for
blepharospasm, 55.2 (9%) for writer’s cramp, 38.0 (6%) for tardive dystonia, 32.3 (5%) for musician’s dystonia, 28.5 (5%)
for psychogenic dystonia, 26.6 (4%) for generalised dystonia, 24.7 (4%) for spasmodic dysphonia, 20.9 (3%) for segmental
dystonia, 15.2 (3%) for arm dystonia and 13.3 (2%) for oromandibular dystonia. Leg dystonia, hemidystonia and complex
regional pain syndrome-associated dystonia are very rare. Compared to previous meta-analytical data, primary or isolated
dystonia is 3.3 times more frequent in our study. When all forms of dystonia including psychogenic, generalised, tardive
and other symptomatic dystonias are considered, our dystonia prevalence is 3.7 times higher than believed before. The real
prevalence is likely to be even higher. Having based our study on treatment necessity, our data will allow better allocation
of resources for comprehensive dystonia treatment.
Keywords Dystonia · Epidemiology · Prevalence · Cervical dystonia · Blepharospasm · Writer’s cramp · Tardive dystonia ·
Musician’s dystonia · Psychogenic dystonia · Functional dystonia · Generalised dystonia · Spasmodic dysphonia ·
Segmental dystonia · Arm dystonia · Oromandibular dystonia · Botulinum toxin therapy
Introduction
* Dirk Dressler
dressler.dirk@mh-hannover.de
1
Movement Disorders Section, Department of Neurology,
Hannover Medical School, Carl-Neuberg-Str. 1,
30625 Hannover, Germany
2
Institute of Music Physiology and Musicians’ Medicine,
Hannover University of Music, Drama and Media, Hannover,
Germany
3
Hildesheim, Germany
4
Department of Neurosurgery, Hannover Medical School,
Hannover, Germany
5
IAB - Interdisciplinary Working Group for Movement
Disorders, Hamburg, Germany
Dystonia was defined in 1984 by the Ad Hoc Committee
of the Dystonia Medical Research Foundation (DMRF) [9]
as the occurrence of sustained involuntary muscle contractions causing twisting, repetitive movements and abnormal
postures.
The current concept of dystonia was developed in the
mid-1980s by C David Marsden and Stanley Fahn [8] when
they—for the first time—unified various hitherto independent conditions under the term dystonia. Dystonia covers a
large number of different manifestations occurring with a
wide spectrum of severities caused by various aetiologies
and probably reflecting numerous different underlying
pathophysiologies. It is still defined entirely by its clinical
phenomenology. Due to its inhomogeneity, various classifications have been proposed.
13
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Journal of Neurology
The relatively recent introduction of the dystonia concept still causes a continued awareness deficit generating
large numbers of undiagnosed patients and complicating
the interpretation of older clinical data. Older clinical data
may also be impaired by outdated classification systems.
Lack of technical parameters may generate diagnostic
uncertainty, at least for the non-expert. Dystonia’s wide
spectrum of manifestations still generates terminological
problems complicating data base searches. It also causes
the separation of dystonia patients into various medical
specialties. Its considerable variability of severities produces large number of mildly affected patients not pursuing contact to the medical system.
All this makes epidemiological studies and their interpretation challenging. We wanted to study the prevalence
of dystonia based on current definitions and classifications
and with a novel service-based approach to generate data,
which are relevant for patients, their therapy and the health
care system.
Methods
Design
The study is a service-based chart review to determine
the point prevalence of dystonia patients requesting and/
or requiring therapy in the City of Hannover on December
31st, 2014.
Patients
Patient inclusion criteria consisted of (1) diagnosis of
dystonia (2) request of the patient and/or requirement as
decided by the physician to undergo treatment (3) registered address within the City of Hannover. There was no
exclusion of specific dystonia forms, such as psychogenic
dystonia, tardive dystonia, axial dystonia, genetic dystonia
etc.
Database
Patients were identified from the general patient database
of the Department of Neurology and the Botulinum Toxin
Therapy Registry of the Movement Disorders Section of
the Department of Neurology of Hannover Medical School.
Databases were maintained and supervised by local movement disorders specialists. A certain proportion of patients
were contributed by two co-authors (EA, RG), also specialised in movement disorders and particularly dystonia.
13
Dystonia population
Dystonia was diagnosed according to the above mentioned DMRF criteria. According to current concepts,
psychogenic dystonia was classified as dystonia, rather
than pseudo-dystonia. Functional dystonia is a synonym
of psychogenic dystonia. Nocturnal oromandibular dystonia, i.e., bruxism, was included in this study. Its relationship to oromandibular dystonia will be discussed below.
Psychogenic dystonia was diagnosed by physical examination and anamnestic features as previously suggested [10].
Tardive dystonia was diagnosed, when dystonia occurred
under or up to 1 year after exposure to dopamine receptor
blocking agent intake for at least 1 month. Dystonia as an
additional symptom in widespread and diffuse brain damage, e.g., perinatal brain damage/infantile cerebral palsy
or hypoxic brain damage, was not included in this study.
Likewise, spasticity including elements of dystonia [5]
was not included in this study. As camptocormia is not
considered to be predominantly dystonic in origin, it was
not included in this study. Axial dystonia, however, was
considered to be dystonic.
Dystonia was classified according to the localisation of
its main manifestation. The main dystonic manifestation
was the manifestation for which treatment was requested
and/or offered. Additional localisations were considered
for classification only, when they were treated. The following localisations were considered: Cervical dystonia (CD):
involvement of neck and shoulder muscles. Blepharospasm
(BS): involvement of periocular muscles. Oromandibular
dystonia (OMD): involvement of perioral, mandibular and
lingual muscles. Spasmodic dysphonia (SD): involvement
of laryngeal muscles. Additional involvement of pharyngeal muscles may be present. Arm dystonia (AD): involvement of arm muscles with spontaneous occurrence. Leg
dystonia (LD): involvement of leg muscles. Segmental
dystonia (SGD): involvement of two or more contiguous
body regions. Hemidystonia (HD): exclusive involvement of muscles in one side of the body. Generalised
dystonia (GD): involvement of muscles in more than one
non-contiguous body regions regardless of their severity. In addition, patients may be classified according to
pathophysiology with task-specific dystonia in the forms
of writer’s cramp (WC) and musician's dystonia (MD).
Other task-specific dystonia such as athlete’s cramps
would have been included, if they would have occurred.
Aetiology may also have been used for classification. In
tardive dystonia (TRD), dystonia was caused by exposure
to dopamine receptor blocking agents, in psychogenic
dystonia (PSY), it was caused by a psychological mechanism. TRD and PSY patients were classified under their
aetiologies rather than under their dystonia localisation.
Journal of Neurology
In complex regional pain syndrome-associated dystonia
(CRPD), a complex regional pain syndrome was believed
to have caused dystonia.
Reference area
The reference area is the City of Hannover. This reference
area was chosen because of its long-established and comprehensive dystonia infrastructure generating a high degree
of dystonia awareness, its barrier-free access to treatment
generating a minimum of unreported cases and few and well
interconnected treatment providers generating a high degree
of data homogeneity.
Dystonia treatment in the reference area
Dystonia treatment in the reference area is provided by five
specialised and interconnected treatment centres.
The Movement Disorders Section of the Department
of Neurology at Hannover Medical School (TC-DD) was
started in 1991 by Professor R Dengler. It was one of the
first centres in Germany providing botulinum toxin therapy.
In 2008, one of the authors (DD) was appointed the first
professor for movement disorders in Germany. In this capacity, he was able to restructure and expand BT operations in
Hannover considerably. He communicated pro-actively with
the regional referring neurologists. He organised teaching
sessions on dystonia and BT therapy for referring neurologists, general practitioners and physiotherapists. He connected with patient organisations and generated an active
media presence. The centre’s primary catchment area is the
whole North of Germany with many patients also coming
from other parts of Germany and the whole of Europe and
the Middle East.
The Department of Neurosurgery of Hannover Medical
School (TC-JKK) directed by Professor JK Krauss operates
an internationally renowned centre for Deep Brain Stimulation and other movement disorders surgery.
The Department of Phoniatry of Hanover Medical School
(TC-MP) is run by Professor M Ptok. He is one of the leading phoniatricians providing BT therapy in Germany.
The Institute of Music Physiology and Musicians’ Medicine at Hannover University of Music, Drama and Media
(TC-EA), directed by Professor E Altenmüller, holds the
world’s largest groups of patients with musician’s dystonia. He directly collaborated in this project and provided
anonymised patient data.
One private neurologist (Niedergelassener Neurologe),
Doctor R Giess (TC-RG), also sees dystonia patients frequently and applies BT therapy. He is serving patients from
all state and private health insurances. He also collaborated
in this project and provided anonymised patient data.
Dystonia therapy is offered at the Movement Disorders
Section according to internationally recognised standards
[4]. The main dystonia treatment is BT therapy. It is offered
for all dystonia indications except PSY. With an annual BT
consumption in excess of 20,000 standard vials of onabotulinumtoxinA, abobotulinumtoxinA, incobotulinumtoxinA and
rimabotulinumtoxinB the Movement Disorders Section is
one the busiest BT centres in Europe. Dystonia forms without official registrations in Germany are covered by off-label
therapy. Except for a nominal prescription fee, BT therapy is
free of charge for all patients. Other dystonia therapies provided, include drug treatments, physiotherapy, occupational
therapy, psychotherapy and re-training programs for musician’s dystonia. Deep brain stimulation is performed by TCJKK frequently in combination with BT therapy. Treatment
of MD is performed by TC-EA, treatment of SD by TC-MP.
Reference population
As provided by the Census Office of the City of Hannover and shown in Table 1, the population of the reference
area on December 31st 2014 was 525,731 with registered
addresses spread over 29 postal areas. The population in
the reference area consists of German nationals and nonGerman inhabitants. The ethnic background of the population is diverse. Depending on the definitions applied, at least
half of the Hannover population is considered of having a
‘migratory background’, i.e., having a foreign nationality
alone or in combination with a German citizenship. About
one third of them coming from the European Union and the
rest mainly from various Islamic countries (official website
of the City of Hannover). The patient’s nationality and ethnic
background was not monitored in this study, nor was there a
way to identify the ethnic composition in the different postal
areas.
Population of Germany
Hannover prevalence data were extrapolated to indicate the
number of dystonia patients in Germany. For this, Statistisches Bundesamt (Census Office of the Federal Republic
of Germany) provided the figure of the population of the
Federal Republic of Germany on December 31st 2014. It
was 81,198,000.
Reference date
The reference date was 31st, December 2014.
Parameters
Study parameters include the point prevalence in the reference area on the reference date (prevalence), the patient’s
13
13
Table 1 Raw data
PA
P [n]
TN [n]
CD [n]
30,159
30,161
30,163
30,165
30,167
30,169
30,171
30,173
30,175
30,177
30,179
30,419
30,449
30,451
30,453
30,455
30,457
30,459
30,519
30,521
30,539
30,559
30,625
30,627
30,629
30,655
30,657
30,659
30,916
total
8865
25,426
23,476
23,498
19,161
9909
16,784
19,223
7080
14,300
16,126
43,076
20,431
16,575
19,947
22,084
19,401
22,779
32,166
19
20,596
22,095
17,991
16,072
16,479
19,478
16,484
16,200
10
525,731
5
27
14
5
6
4
15
6
10
5
10
18
9
4
13
14
9
17
20
0
8
20
13
22
13
14
9
11
0
316
5
9
4
2
3
4
3
3
2
5
6
3
2
6
6
3
7
9
BS [n]
3
2
3
4
WC [n]
OMD [n]
MD [n]
SD [n]
7
3
1
2
1
2
1
1
GD [n]
SGD [n]
2
2
1
AD [n]
HD [n]
LD [n]
3
7
6
13
5
6
3
7
2
1
1
4
132
46
2
1
1
TRD [n]
2
2
CRPD [n]
1
1
4
1
1
1
1
2
4
3
1
1
3
3
1
2
2
PSY [n]
1
1
1
1
1
1
1
1
5
1
1
1
1
1
2
3
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
5
2
1
1
1
1
29
1
1
1
1
1
3
2
1
1
1
1
1
1
1
1
1
4
1
1
4
1
7
1
1
1
1
17
13
1
1
1
1
3
3
1
2
2
1
14
1
11
8
1
2
15
20
1
PA postal area, P population, TN total number of dystonia patients, CD cervical dystonia, BS blepharospasm, WC writer's cramp, OMD oromandibular dystonia, MD musician’s dystonia, SD
spasmodic dysphonia, GD generalised dystonia, SGD segmental dystonia, AD arm dystonia, HD hemidystonia, LD leg dystonia, PSY psychogenic dystonia, TRD tardive dystonia, CRPD CRPSassociated dystonia
Journal of Neurology
Prevalence of dystonia in the City of Hannover and its postal areas
Journal of Neurology
name (name), the patient’s sex (sex), the patient’s age on
reference date (age), the patient’s address on reference date
(postal area), the patient’s diagnosis (diagnosis) and information about the application of BT therapy.
Ethical approval
The study was performed under the regulations of the local
ethical committee of Hannover Medical School.
CD prevalence
CD patients are 63.8 ± 13.9 years. Their male/female ratio
is 0.3. 42% of all dystonia patients suffer from CD. It is by
far the most common dystonia manifestation. Its prevalence
is 251.1/1mio. Extrapolation suggests 20,387 CD patients
in Germany. 94% of patients accepted BT therapy, 6% preferred other therapies or did not wish therapy.
BS prevalence
Results
Data source
89% patient data of this study originated from TC-DD, 6%
from TC-EA and 5% from TC-RG. Patients from TC-EA
included 18 patients with MD and 3 patients with WC.
BS patients are 69.4 ± 12.5 years. Their male/female ratio is
0.4. 15% of all dystonia patients suffer from BS. It is the second most common dystonia manifestation. Its prevalence is
87.5/1mio. Extrapolation suggests 7105 BS patients in Germany. 98% of patients accepted BT therapy, 2% preferred
other therapies or did not wish therapy.
WC prevalence
Raw data
Table 1 shows the raw data acquired in this study. The prevalence in the postal areas range from 212.8 to 1412.4/1mio.
Total prevalence
The epidemiological data obtained in this study are shown in
Table 2. Altogether 316 dystonia patients were identified in
the reference area on the reference date. This equals a point
prevalence of 601.1/1mio. Extrapolation suggests that there
should be 48,806 dystonia patients in Germany.
WC patients are 62.0 ± 16.6 years. Their male/female ratio
is 0.5. 9% of all dystonia patients suffer from WC. It is the
third most common dystonia manifestation. Its prevalence is
55.2/1mio. Extrapolation suggests 4479 WC patients in Germany. 59% of patients accepted BT therapy, 41% preferred
other therapies or did not wish therapy.
TRD prevalence
TRD patients are 67.0 ± 19.7 years. Their male/female
ratio is 0.3. 6% of all dystonia patients suffer from TRD.
Table 2 Epidemiological data of the Hannover cohort
Dystonia form
Age
[years/mean±SD]
Sex ratio
[m:f]
Frequency
[% of all dystonia
patients]
Prevalence
[n/1mio]
Extrapolated prevalence in Germany
[n]
Cervical dystonia
Blepharospasm
Writer's cramp
Tardive dystonia
Musician's dystonia
Psychogenic dyst
Generalised dystonia
Spasmodic dysphonia
Segmental dystonia
Arm dystonia
Oromandibular dyst
Leg dystonia
Hemidystonia
Total
63.8 ± 13.9
69.4 ± 12.5
62.0 ± 16.6
67.0 ± 19.7
50.2 ± 14.4
47.2 ± 20.8
51.7 ± 14.8
60.4 ± 17.5
62.6 ± 13.5
70.5 ± 12.5
46.7 ± 15.8
0.3
0.4
0.5
0.3
1.8
1.1
0.3
0.4
0.2
0.6
0.8
251.1
87.5
55.2
38.0
32.3a
28.5
26.6
24.7
20.9
15.2
13.3
20,387
7105
4479
3089
2626a
2317
2162
2008
1699
1236
1081
62.4 ± 16.1
0.4
42
15
9
6
5a
5
4
3
3
3
2
1
0
100
601.1
48,806
a
Explanation in Discussion
13
Journal of Neurology
It is the fourth most common dystonia manifestation. Its
prevalence is 38.0/1mio. Extrapolation suggests 3089
TRD patients in Germany. 65% of patients accepted BT
therapy, 35% preferred other therapies or did not wish
therapy.
MD prevalence
MD patients are 50.2 ± 14.4 years. Their male/female ratio is
1.8. 5% of all dystonia patients suffer from MD. With this, it
would be the fifth most common dystonia manifestation. Its
prevalence is 32.2/1mio. Extrapolation suggests 2626 MD
patients in Germany. This seemingly high prevalence will be
discussed below. All patients accepted trials of BT therapy.
PSY prevalence
PSY patients are 47.2 ± 20.8 years. Their male/female ratio
is 1.1. 5% of all dystonia patients suffer from PSY. It is the
sixth most common dystonia manifestation. Its prevalence
is 28.5/1mio. Extrapolation suggests 2317 PSY patients in
Germany. Therapeutic recommendations were based on psychotherapy and physiotherapy, which were accepted by all
patients. Antidystonic pharmacotherapy was not offered.
GD prevalence
GD patients are 51.7 ± 14.8 years. Their male/female ratio
is 0.3. 4% of all dystonia patients suffer from GD. It is the
seventh most common dystonia manifestation. Its prevalence
is 26.6/1mio. Extrapolation suggests 2162 GD patients in
Germany. 64% of patients accepted BT therapy, alone or in
combination with other therapies. 36% received other therapies usually including deep brain stimulation.
SD prevalence
SD patients are 60.4 ± 17.5 years. Their male/female ratio
is 0.4. 3% of all dystonia patients suffer from SD. It is the
eighth most common dystonia manifestation. Its prevalence
is 24.7/1mio. Extrapolation suggests 2008 SD patients in
Germany. 85% of patients accepted BT therapy. 15% preferred other therapies, usually speech therapy, or did not
receive any treatment.
SGD prevalence
SGD patients are 62.6 ± 13.5 years. Their male/female ratio
is 0.2. 3% of all dystonia patients suffer from SD. It is the
ninth most common dystonia manifestation. Its prevalence
13
is 20.9/1mio. Extrapolation suggests 1699 SGD patients in
Germany. All patients accepted BT therapy.
AD prevalence
AD patients are 70.5 ± 12.5 years. Their male/female ratio
is 0.6. 3% of all dystonia patients suffer from SD. It is the
tenth most common dystonia manifestation. Its prevalence is
15.2/1mio. Extrapolation suggests 1236 AD patients in Germany. 63% of patients accepted BT therapy, 37% preferred
other therapies or chose not to be treated.
OMD prevalence
OMD patients are 46.7 ± 15.8 years. Their male/female
ratio is 0.8. 2% of all dystonia patients suffer from OMD.
It is the eleventh most common dystonia manifestation. Its
prevalence is 13.3/1mio. Extrapolation suggests 1081 OMD
patients in Germany. All patients accepted BT therapy.
Four of our OMD patients had nocturnal occurrence, only,
three had continuous OMD. The age of the nocturnal OMD
patients was 40.3 ± 7.3 years.
LD prevalence
LD is extremely rare only occurring as a levodopa induced
transient drug adverse effect in a patient with advanced idiopathic Parkinson’s disease.
HD prevalence
HD is also extremely rare occurring in a single patient with
contralateral basal ganglia damage.
CRPD prevalence
CRPD is another extremely rare condition only seen in a
single patient.
Discussion
Definitions, classifications
The dystonia definition used here is the current one. It is
based on the clinical symptomatology of the dystonic muscle hyperactivity. Unlike in previous studies, it includes
psychogenic dystonia, rather than separating it as pseudodystonia. Other diagnostic systems previously used, such as
the International Statistical Classification of Diseases and
Related Health Problems (ICD), Diagnostic and the Statistical Manual of Mental Disorders (DSM) do not reflect our
current understanding of dystonia.
Journal of Neurology
The dystonia classification used in our study is currently
the most frequently used one. It tries to reflect clinical needs
as it is mainly based on dystonia localisation. It also reflects
sectorial aspects of the health care system, such as treatment
in different medical specialties. However, in our study we
extended the classification system to include pathophysiology, such as task-specificity (WC, MD). Symptomatic
aetiology as in diffuse brain damage (perinatal brain damage/infantile cerebral paresis, hypoxic brain damage) was
excluded in our study, as the clinical symptomatology is
usually dominated by non-dystonic features and so is its
treatment. Localised brain damage, however, was included,
although only one HD patient with focal contralateral basal
ganglia lesion occurring in temporal relationship was identified. TRD as another symptomatic aetiology was included,
as it is a rather common dystonia form and as its iatrogenic
origin deserves special medical attention. In addition, its
clinical features are specific and require special therapeutic approaches. Altogether, our classification is similar to
a recently suggested one [1]. It was not the purpose of this
study to suggest a novel classification system or to decide
on the appropriateness of existing classification system. The
data reported here can easily be fitted in any of the existing
classification systems to allow comparisons.
Design
The gold standard design to determine the prevalence of a
disease in a population would be to examine this entire population by an expert. This approach is called door-to-door
survey. However, such an approach is not feasible in dystonia for several reasons: the presumed dystonia prevalence is
so low, that extremely large populations would have to be
screened to keep statistical errors reasonably low. In addition, the severity spectrum of dystonia is extremely large, so
that such an approach would retrieve large numbers of persons, where dystonia might be a subtle finding rather than a
complaint without a consequence for the patient or the health
care system. This is a frequent finding, when we examine
family members of our dystonia patients, or when we examine dystonia patients in all of their body parts. We, therefore,
decided to use a pragmatic approach by focussing our study
on the patient and its therapy and the health care system
requirements (Table 3). We chose to set the entry level into
our study to level 5, where the patient seeks treatment and/
or the physician recommends it. With this modified servicebased approach, we are confident to best serve the patients'
interest in recognition and awareness and the health care
system's requirements for planning resource allocation.
Research interests, such as describing the full spectrum of
dystonia severities, would have required different designs.
The reference area used in our study had the advantage,
that barrier-free dystonia treatment has been available for
Table 3 Levels of dystonia severity
Level
Description
1
2
Dystonia is noticed by a specialist only
Dystonia is noticed by non-specialist
observers, not by the patient
Dystonia is noticed by the patient
Patient seeks diagnosis, not treatment
Patient seeks treatment and/or physician suggests treatment
Patient receives treatment
3
4
5
6
many years. This should have increased dystonia awareness
and should have reduced unreported cases. Both issues have
been major problems in previous studies.
Dystonia treatment provided by few interconnected treatment centres in the reference area may look as a methodological disadvantage. However, we believe it increased data
homogeneity and, thus, actually increased the study quality.
Previous studies
So far, there have been some 25 studies published on the
epidemiology of dystonia. For review, see [7, 11, 12]. One
of these studies provides a meta-analytical comparison [12].
As the design of the original studies varies enormously, so
do their results. Table 4 shows design features influencing
the results of epidemiological studies. Meta-analytical data
[12] combining these vastly different study designs suggest
the figures shown in Table 5.
Overall prevalence
The prevalence of all patients with dystonia in our study
is 601.1/1mio. This includes a prevalence of 47.5/1mio
for patients with non-focal dystonia (SGD = 20.9/1mio,
GD = 26.6/1mio), a prevalence of 28.5/1mio for patients
with psychogenic dystonia and a prevalence of 44.6/1mio
for patients with symptomatic dystonia (TRD = 38.0/1mio,
HD = 1.9/1mio, CRPS = 1.9/1mio), LD = 3.8/1mio). It also
includes a prevalence of 32.3/1mio for patients with MD
which is often not included in previous studies.
Three previous studies will now be discussed in detail,
as they are similar to our study. A service-based study from
Ireland [13] includes CD, BS, focal hand dystonia, SD, MD
and OMD, but excludes PSY, SGD, GD, TRD, HD and
CRPS. It reports an overall prevalence of 178/1mio. Our
matched overall prevalence for these patient groups would
be 464.1/1mio indicating a prevalence 2.6 times higher than
previously thought. When PSY, non-focal and symptomatic
dystonia (TRD, HD, CRPS) are included, our total prevalence is 3.4 times higher than previously thought. 17.2% of
13
Journal of Neurology
Table 4 List of design details
different in epidemiological
studies
Design feature
Examples
Dystonia definition
DMRF definition
ICD definition
DSM definition
Segmental dystonia
Multifocal dystonia
Generalised dystonia
Psychogenic dystonia
Dystonic tremor
Definition of dystonic tremor
Definition of psychogenic dystonia
Definition of oromandibular dystonia/bruxism
Media campaign and self-reporting
Non-specialists
Movement disorders specialists
Multiple independent examiners
No relevance threshold (door-to-door survey)
Treatment threshold (service based designs)
Since 1970
Public and medical awareness
Availability of classification systems
Availability of treatment options
Availability of reliable data bases
1–879 [3]
707–5.8mio [12]
Ethnic composition
Central registries
Local data base in movement disorders centre
Centralised system
De-centralised system
Dystonia classification
Diagnostic criteria
Diagnostic quality
Dystonia severity
Time and place of data acquisition
Sample size of dystonia population
Sample size of reference population
Type of reference population
Type of data base
Health care system structure
Table 5 Comparison of meta-analytical data provided by [12] with our data
Dystonia form
All
Primary/isolated dystonia
Focal and segmental dystonia
Cervical dystonia
Blepharospasm
Limb dystonia
Writer's cramp
Oromandibular dyst
Laryngeal dystonia
Generalised dystonia
13
Prevalence
[n/1mio]
Corrections to match Steeves et al.
Steeves et al.
Our data
164.3
153.6
49.8
42.4
12.4
16.5
5.2
15.4
4.4
601.1
527.0
500.4
251.1
87.5
15.2
55.2
13.3
24.7
26.6
total
total minus: TRD, CRPS, HD, LD, PSY
total minus: TRD, CRPS, HD, LD, PSY, GD
CD
BS
AD
WC
OMD
SD
GD
Ratio
[Our prevalence/prevalence of Steeves et al.]
3.2
3.3
5.0
1.8
1.2
3.3
2.5
1.6
6.0
Journal of Neurology
the Irish patients suffered from BS, which was thought to be
so exceptionally low, that the authors attributed this to Ireland's reduced sunlight intensity [13]. Comparing this to our
BS prevalence of 87.5/1mio with similar sunlight intensity
as in Ireland, makes this explanation unlikely.
Another very recent register study from Finland [11]
includes CD, BS, WC + AD, SD, OMD, LD, focal axial,
SGD, multifocal dystonia and GD and found a total dystonia
prevalence of 405/1mio. Matching our overall prevalence
data to this study design would generate a prevalence of
498.3–1.2-fold more than previously reported.
The third study is a meta-analytical study [12]. It is
compared to our results in Table 5. For primary dystonia,
our prevalence is 3.3 times higher than previously thought.
When all forms of dystonia including PSY, GD, TRD and
other symptomatic dystonias are considered, our dystonia
prevalence is 3.7 times higher.
In the following, we will comment on the epidemiology
of individual dystonia forms.
CD: It may present with tonic, clonic and tremulous elements. Its pathognomonic feature is the geste antagoniste.
The best know form of CD is the tonic one. Tremulous CD
is the least known one. CD may, therefore, often be misdiagnosed as ET or Parkinson’s disease. Properly diagnosing
tremulous dystonia becomes especially challenging, when
tonic elements are missing. Therefore, we belief that CD,
especially in its tremulous form, is substantially underdiagnosed. Tics are another differential diagnosis of CD. In
addition, CD may be misinterpreted as nervousness or some
other form of psychological instability. As in most other
epidemiological studies, CD is the most common form of
dystonia.
BS: It is the second most common form of dystonia. If
it additionally involves perioral or mandibular muscles, the
term Meige syndrome is used. Facial motor tics and hemifacial spasms are differential diagnoses. Psychogenic tics are
extremely rare. Especially, when BS comes together with
apraxia of eyelid opening, which may be the case in 30–50%
of BS patients, BS may be misinterpreted as myasthenia
gravis. In ophthalmology, BS is sometimes misdiagnosed as
dry eye syndrome. BS may still be underdiagnosed.
WC: It is the third most common dystonia. It is characterised by its task specific occurrence, at least initially. Not
infrequently, it is misdiagnosed as essential tremor, especially when it occurs in a clonic or tremulous form. Its severity covers a wide range. Often, it is not recognised by the
patient, especially as neat handwriting these days becomes
less and less of a necessity. In other patients with mild WC,
diagnosis may be requested, but not therapy. These patients
were not included in our study. Our standard treatment for
WC is BT therapy. In mild cases and in cases with predominant finger involvement anticholinergic treatment may be
tried first. Shifting writing to the non-dominant hand is also
recommended to all of our patients. All of these patients
were included in our study, as they requested and received
therapy. WC is a relative frequent additional sign in patients
with CD. In most of these cases, no treatment is requested
so that these patients were not classified as having segmental dystonia. Overall, the high percentage of patients with
mild forms of WC may contribute to considerable underdiagnosing of WC. BT therapy in WC has a low acceptance
rate. This reflects problematic efficacy and frequent adverse
effects of BT therapy. With increased experience over time,
our results increased considerably, so that willingness to
undergo a recommended BT therapy also increased. Regular use of ultrasound guidance further increased results and
therapy willingness.
MD: It is another task-specific dystonia. It is a common
problem amongst professional musicians affecting probably
around 1% of them [2]. MD prevalence of 32.3/1mio in our
study is much higher than the 5.11/1mio MD prevalence
previously calculated [13]. Our figure most likely reflects
a special situation, as the University of Music, Drama and
Media and four professional orchestras and Germany’s
second largest conservatory attract large numbers of musicians to the reference area. Whether Irish data on MD in the
normal population are representative for other populations,
need to be studied, as the proportion of musicians in the
Irish population may be higher than elsewhere. The male
preponderance seen in our study, was also reported previously [2, 13],
TRD: It is the fifth most frequent dystonia. TRD
describes the aetiology of a dystonia rather than its localisation in the body. In TRD exposure to neuroleptics and
other dopamine receptor blocking agents is the cause of dystonia. TRD usually consists of mixed dystonia with tonic,
clonic and tremulous elements. It is predominantly localised
in oromandibulolingual muscles. Periocular and axial muscles are also frequently affected. We feel, that over the last
20 or 30 years with the development of atypical and second generation neuroleptics the overall prevalence of TRD
has come down. In addition, we feel that their presentation
has changed with rapid lingual movements occurring less
frequently. Low acceptance of BT therapy in TRD may be
caused by difficult to treat dystonia manifestations and psychiatric co-morbidity.
PSY: It is the sixth most frequent dystonia. It describes
dystonia of psychogenic origin. It is often localised in the
arms and the neck. In the past, it was often termed pseudodystonia, but according to our current understanding, it is
considered true dystonia. It is rarely if ever included in
epidemiological studies on dystonia. Hints towards PSY
include rapid onset, intermittent course, symptomatology
mixing different movement disorders, demonstrative character, distractibility, changes in various functional contexts and co-existence of non-motor signs and multiple
13
Journal of Neurology
complaints. Psychiatric co-morbidity is more frequent than
in the normal population. It may be difficult to diagnose
for the non-expert. As we know very little about the time
course of the condition, the real prevalence of PSY is difficult to estimate as spontaneous remissions may occur
before the patient is connected to an expert.
GD: It is the seventh most frequent dystonia. As outlined above, GD describes the localisation of dystonia. It
does not necessarily describe the severity of dystonia. In
the past, this distinction was not always consequently followed, so that wide-spread, but less severe dystonia may
not have been named GD. Treatment includes deep brain
stimulation, BT therapy (alone or in combination with
deep brain stimulation) and drug therapy.
SD: It is the eighth most common form of dystonia.
In mild forms, it may produce hoarseness of voice only,
sometimes leading to the misdiagnosis of chronic infection. In more severe cases, SD may be the cause of major
disability. SD patients in this study were either primarily
seen by TC-DD and then sent to TC-MP for confirmation
of diagnosis and treatment, or they were primarily seen
and treated by MP and then sent to DD for a comprehensive dystonia work-up. SD is a relatively common additional manifestation of CD and other, more wide-spread
forms of dystonia.
SGD: It is the ninth most common form of dystonia.
It usually consists of CD and arm involvement. Mild arm
involvement is relatively common. Our data only include
arm involvement if therapy is required and/or requested.
AD: It is the tenth most common form of dystonia. Isolated AD is rare. It may have developed from task- specific
dystonia, when this has become continuously occurring.
OMD: It is the eleventh most common form of dystonia. According to our definitions, OMD excluded all
patients with oromandibular dystonia caused by neuroleptics exposure. In four of the seven patients with OMD
seen here, OMD was nocturnal, so that the term bruxism
may be used. None of those patients had a positive family history; one had additional signs of CD. Two of the
three patients with continuous OMD had a positive family
history. We believe that nocturnal OMD, conventionally
called bruxism, may in fact be an attenuated form of OMD.
If that would be the case, the overall incidence of dystonia
would be considerably higher than currently believed.
LD: It is an extremely rare form of dystonia. In early
onset dystonia it is usually a transient stage in the development of DYT1-positive generalised dystonia. Our two
LD patients suffered from iatrogenic dopa-induced leg
dystonia.
HD: is also a very rare condition caused by contralateral basal ganglia damage, as it was the case in our patient.
CRPD: It is another very rare form of dystonia. Chronic
pain syndromes including CRPS seem to have the potential
13
to produce movement disorders, such as painful leg and
moving toe syndrome [6].
Conclusions
Prevalence figures of dystonia are heavily influenced by
numerous methodological aspects including dystonia definition, dystonia classification, diagnostic criteria, diagnostic quality, time and place of data acquisition, sample sizes
of dystonia population and reference population, type of
reference population, type of data base and structure of the
health care system. We chose design parameters to provide
data relevant to the patient's therapy and the health care
system requirements.
For this, we used the current dystonia definition, the
current dystonia classification without excluding any dystonia group, using dystonia experts for diagnostic quality
and chose the need for therapy as the severity parameter.
The reference population was a large unbiased central
European one with a well-established comprehensive
dystonia infrastructure, barrier free treatment and a high
degree of dystonia awareness all contributing to high dystonia retrieval rates.
Our adjusted overall dystonia prevalence is more than
double the prevalence of the latest comparable study.
When PSY and symptomatic dystonia such as TRD, HD
and CRPD are included, our prevalence more than triples
the previous one.
As with all service-based prevalence studies a certain
unidentified proportion of dystonia patients remains. How
big this proportion is, remains unclear. Further retrieval
rate studies will have to address this.
Prevalence figure provided in this study may be used
to plan resource allocation for comprehensive dystonia
therapy.
Acknowledgements The authors are grateful for a grant from the IngeDiesbach-Stiftung. The authors are also grateful for the support of the
Census Office of the City of Hannover.
Funding Open Access funding enabled and organized by Projekt
DEAL.
Declarations
Conflicts of interest DD received honoraria for services provided
to Allergan, Ipsen, Merz, Lanzhou Institute of Biological Products,
Medy-Tox, Revance, Desitin, Syntaxin, AbbVie, Medtronic, St Jude,
Boston Scientific, Almirall, Bayer, Sun, Teva, UCB, IAB—Interdisciplinary Working Group for Movement Disorders. He is shareholder
of Allergan and holds patents on botulinum toxin and botulinum toxin
therapy. FAS is founder and owner of IAB—Interdisciplinary Working Group for Movement Disorders. She received reimbursement
from Abbot, AbbVie, Almirall, Allergan, Bayer, Desitin, Dynamed,
Hempel GesundheitsPartner, Ipsen, Johnson & Johnson, Licher, Meda,
Journal of Neurology
Medtronic, Merz, Orion, PTZ Nawrath, Sensomotorik & Rehabilitation Hellmuth & Thiel, Sintetica, Sporlastic, Sun, Teva, Tricumed,
TRS Med, UCB. RG has nothing to disclose. EA has nothing to disclose. JKK is a consultant to Medtronic and to Boston Scientific. His
research is supported by Deutsche Forschungsgemeinschaft (Project
#201925000).
5.
Ethical approval The study was performed under the regulations of the
local ethical committee of Hannover Medical School.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
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included in the article's Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article's Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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