Full text of DOI:10.1097/00005537-200202000-00004

The Laryngoscope
Lippincott Williams & Wilkins, Inc., Philadelphia
© 2002 The American Laryngological,
Rhinological and Otological Society, Inc.
Risk Factors and Demographics in Patients
With Spasmodic Dysphonia
John M. Schweinfurth, MD; Mark Billante, BS; Mark S. Courey, MD
Objectives: Spasmodic dysphonia has been char-
acterized as a functional, psychogenic, or movement
disorder with no known etiology or cure. In the
present study, risk factors associated with other
movement disorders were evaluated in patients with
spasmodic dysphonia. Study Design: Retrospective
patient survey of 168 patients with a known diagnosis
of spasmodic dysphonia who completed question-
naires at the time of interval botulinum toxin injec-
tion. Methods: Patients completed questionnaires on
demographics, education level, work history, signifi-
cant life events, medical, social, and family history.
The results were compared with those of first-degree
relatives as a control group with similar demograph-
ics. Data were analyzed using percentages calculated
on the total number of responses and distribution of
frequency of each. Statistical significance was esti-
writer’s cramp but no history of major illness or other
neurological disorder. There appear to be no signifi-
cant environmental or hereditary patterns in the eti-
ology of spasmodic dysphonia. Stress or viral infec-
tion may induce the onset of symptoms of spasmodic
dysphonia. Many features of the disorder are common
to other movement disorders, and this knowledge
may direct future research efforts. Key Words: Spas-
modic dysphonia, dystonia, etiology, stress, viral
infection.
Laryngoscope, 112:220–223, 2002
INTRODUCTION
Dystonia is defined as a syndrome of sustained, un-
controlled muscle contractions resulting in abnormal, un-
intended actions.1 Spasmodic dysphonia is considered to
be one form of an idiopathic adult-onset dystonia that
exhibits focal manifestations. Other focal dystonias with a
presumed similar etiology include spasmodic torticollis,
blepharospasm, writer’s cramp, and trunk and foot
dystonia.
2
mated on t tests of ␹ values. Results: In the series of
168 patients, there was a female predominance of 79%.
Age range at onset was 13 to 71 years with an average
of age of 45 years. Sixty-five percent of patients had
previously had the measles or mumps compared with
the national average of 15% in a similar age group
(P ؍ .0001). Thirty percent of patients directly associ-
ated onset of spasmodic dysphonia symptoms to an
upper respiratory tract infection, and 21% to a major
life stress. There was no significant incidence of any
other medical or neurological condition or symptom-
atology. There was no family history of spasmodic
dysphonia. Twenty-six percent of patients had an es-
sential tremor compared with 4% of first-degree rela-
tives (P ؍ .0001), and 11% had associated writer’s
cramp compared with 2% of relatives (P ؍ .02). Less
than 1% of patients described a history of toxic expo-
sure or electrical injury. Conclusions: The majority of
patients with spasmodic dysphonia are girls and
women. A significantly higher incidence of childhood
viral illness was found in the patients with spasmodic
dysphonia. Patients with spasmodic dysphonia had a
significant incidence of both essential tremor and
The cause or origin of spasmodic dysphonia and other
focal dystonias remains unknown. Historically, spasmodic
dysphonia has been thought to be psychogenic or trau-
matic in origin.2 Risk factors for certain types of nonfocal
dystonia have been well delineated. These range from
patterns of autosomal inheritance to acquired genetic mu-
tations, trauma, stress, electrical injury, viral and psychi-
atric illness, heavy metal poisoning, hydrocephalus, de-
generative cortical diseases, and endocrine disorders.3–13
The purpose of the present study was to determine any
possible association between known risk factors for other
nonfocal dystonias and spasmodic dysphonia.
PATIENTS AND METHODS
One hundred sixty-eight consecutive patients presenting for
botulinum toxin injections for spasmodic dysphonia completed a
questionnaire (Appendix). In addition to a complete medical and
social history, environmental, industrial, geographical, and edu-
cational data were obtained. First-degree relatives were chosen
as control subjects. A complete history was obtained for 186
control subjects. Both patient and control subject shared similar
geographic and environmental history. Geographical information
was restricted to size and economy of place of birth and later sites.
Subjects were asked about conditions affecting first- and second-
degree relatives. In addition, information about individuals living
in the same area was obtained where possible from the subjects’
Presented at the Meeting of the Southern Section of the Triological
Society, St. Petersburg, FL, January 15, 2000.
From the Department of Otolaryngology, Vanderbilt University,
Nashville, Tennessee, U.S.A.
Editor’s Note: This Manuscript was accepted for publication Septem-
ber 12, 2001.
Send Correspondence to John M. Schweinfurth, MD, MC H091,
Hershey Medical Center, 500 University Drive, Hershey, PA 17033, U.S.A.
Laryngoscope 112: February 2002
220
Schweinfurth et al.: Spasmodic Dysphonia

knowledge. Patients and control subjects were asked specifically
about all published risk factors for dystonia. Data were analyzed
by percentages calculated from the total number of responses and
the distribution of frequency. Statistical significance was esti-
mated on paired, two-tailed t tests of ␹2 values (Statview, version
V.1, Abacus Concepts, Inc., Berkeley, CA).
Diagnosis of spasmodic dysphonia was first made by a phy-
sician and a speech pathologist based on criteria in widespread
use and described in the literature.14,15 Patients with segmental
dystonias such as Meige’s disease were excluded from the study
and are not treated with botulinum toxin injection at the Hershey
Medical Center (Hershey, PA). After a careful review and discus-
sion with neurologists at our institution, we have not identified
cases in which benefit was added through the use of magnetic
resonance imaging; therefore, routine imaging of the head and
neck in cases of spasmodic dysphonia was not performed in these
patients.
DISCUSSION
In the current study, a 79% female predominance in
spasmodic dysphonia, as well as an association with child-
hood infectious disease, writer’s cramp, and essential
tremor, was identified. The average age was 56.7 years,
and median age, 56 years. A strong connection with child-
hood viral illness was also noted with 65% of patients
having had the measles or mumps. With respect to neu-
rological findings, there was an association with upper-
extremity essential tremor and, to a lesser degree, writer’s
cramp. In each patient, the manifestations of spasmodic
dysphonia remained focal. Fifty-one percent of patients
associated the onset of symptoms with an acute upper
respiratory tract illness or a major life stress. However,
this finding was well within confidence intervals of the
expected frequency of such occurrences within the general
population. There was no identifiable familial association
with spasmodic dysphonia. Geographical history does not
appear to be relevant to the etiology of spasmodic
dysphonia.
There are a number of inherent biases in examining
the patient population of a given practice area, including
referral, age, and sex bias. By examining trends between
similar studies, some of the biases may be ruled out. Onset
of symptoms in the middle decades of life has been noted
in studies of patients with spasmodic dysphonia, as well
as those of other focal types of dystonia.17,18 Another pre-
viously cited epidemiological finding is female predomi-
nance. This was noted initially by Izdebski et al.,18 which
they did not believe established “spastic dysphonia as a
predominantly female disorder.” This issue was re-
examined by Adler et al.,19 who reviewed their own data,
as well as five other published reports, and concluded that
female predominance is not a result of ascertainment bias.
They were able to find only one report of a higher male
ratio in spasmodic dysphonia.19 In a review of more than
900 patients with primary laryngeal dystonia, Blitzer et
al.20 recorded a 63% female predominance. Therefore, the
finding of female predominance is most likely an accurate
cross-section of the population of patients with spasmodic
dysphonia and is not related to ascertainment bias.
The reason for a predilection toward female sex in a
disorder currently thought to be neurological in origin is
unclear. The predominance of autoimmune diseases in
female patients is thought by some authors to be a phe-
nomenon of microchimerism.21 This theory holds that
persistent fetal cells in the mother’s circulation after preg-
nancy may be responsible for the autoimmune phenome-
non as a result of a mechanism similar to graft-versus-
host disease. A precedent in neurological disorders exists
in multiple sclerosis, which has features of other autoim-
mune disorders.22 This theory does not explain disease
occurrence in nonparous female patients; yet, the paral-
lels are compelling and certainly warrant further investi-
gation into this area.
RESULTS
Thirty-four male and 134 female patients were in-
cluded in the study. Included in the control group were 89
male and 97 female relatives. Age range at onset of spas-
modic dysphonia was 13 to 71 years with a mean age of 45
years. Mean age at the time of treatment was 56 years.
Fifty-five percent were born and lived for an average of 19
years in a rural area with a population of less than
150,000 individuals, then moved to an industrial area
with a population of more than 150,000. No relatives or
individuals living in the same area as the patients with a
diagnosis of spasmodic dysphonia were identified. The
average patient had completed 2 years of college.
Sixty-five percent of patients had previously had the
measles or mumps. This is statistically significantly dif-
ferent from the national average incidence of 17% under
the age of 25 years during the period between 1958 and
1962 (P ϭ .0001). Thirty percent of patients directly asso-
ciated onset of spasmodic dysphonia to an upper respira-
tory tract infection, and 21% to a major life stress (confi-
dence interval [CI], 15%–42%).
Eleven percent of patients had associated writer’s
cramp compared with 2% of individuals in the control
group (P ϭ .02). Associated features of other movement
disorders were observed. Twenty-six percent of patients
had an essential tremor of the upper extremities com-
pared with 4% of first-degree relatives (P ϭ .0001). De-
spite these findings, there was no significant incidence of
any other major medical or neurological condition or
symptomatology. All of the patients exhibited stable focal
disease without segmental spread over a mean interval of
11 years. The incidence of peripheral vascular concurrent
hypertension at 25% was similar to a 27% rate in the
father and a 43% rate in the mother. One patient de-
scribed a history of toxic exposure, and one an electrocu-
tion injury. There were no other cases of associated injury.
The Voice Handicap Index and Short-Form 36 sur-
veys were administered to this same group of patients
before and after treatment with botulinum toxin. Im-
provements in the patients’ perception of their functional,
physical, and emotional voice handicap were statistically
significant. In addition, treatment improved their social
functioning and their perception of their mental health.16
Examination of geographical data may give informa-
tion about possible environmental exposure during child-
hood that could potentially cause the disorder. Geograph-
ical data obtained indicates a rural prevalence during the
developmental years and an industrial or large-city envi-
ronment in adulthood. Most likely, this phenomenon is
Laryngoscope 112: February 2002
Schweinfurth et al.: Spasmodic Dysphonia
221

more closely related to referral pattern bias, the south-
central location of our treatment facility, and the overall
trend of urban migration patterns in the United States.
Incidence of toxic exposure leading to disease development
is sporadic and does not appear to be associated with the
development of spasmodic dysphonia because there was
no incidence of spasmodic dysphonia in the control group,
despite similar environmental exposure. This information
may become useful in future studies as more becomes
known about the effects of specific toxins.
An incidence of childhood measles and mumps infec-
tion of 65% in individuals with spasmodic dysphonia was
discovered in the present study. Izdebski et al.18 reported
a 45% incidence of these illnesses and also noted that
patients with spasmodic dysphonia typically contracted
these illnesses later in life than control subjects. In the
present study, age at onset of disease was not examined
because objective medical records were not consistently
available. Between 1958 and 1962, an average number of
cases of measles per year of 503,282 was reported in the
United States.23 Reporting of mumps cases did not begin
until 1968. In that year, 152,209 cases were recorded.
Assuming that the vast majority of patients contracted the
measles before the age of 25 years, this approximates an
incidence of 15%.24 The potential for latent viral diseases
to cause neurological manifestations is well described in
the case of chickenpox and herpes zoster. There are also
reports in the literature of ataxia following measles,
mumps, and rubella vaccine.25
An association of essential upper-extremity tremor
with other types of dystonia has been noted in other stud-
ies but was found to be common in first-degree relatives as
well.14,26 The present study recorded similar results.
Marsden and Sheehy27 were among the first to iden-
tify spasmodic dysphonia as a manifestation of adult-
onset torsion dystonia. Greene et al.28 found that symp-
toms in the majority of patients with onset after age 21
years remained focal, and only 15% to 30% eventually
developed symptoms outside the initially involved seg-
ment. The authors also found a family history of dystonia
of 3% or less. Therefore, our findings of no spread of
disease and no familial association are correlated in other
studies of dystonia.
Previous studies have suggested that radiographi-
cally significant basal ganglia or brainstem lesions can
cause focal or segmental dystonia.29,30 Lesions in the pu-
tamen, thalamus, and inferior olives have been associated
with spasmodic dysphonia.5,31 In a study of three patients
with spasmodic dysphonia and a history of head trauma,
Finitzo et al.32 noted abnormal findings on magnetic res-
onance imaging in one patient, but abnormal brain elec-
trical activity mapping in all three. Defazio et al.,26 as well
as the present study, noted no history of head trauma or
radiographic lesions. However, they did note an associa-
tion between trauma to an area of the body and later
development of dystonic symptoms, as with cervical dys-
tonia. Our patient population had no focal neurological
findings or suggestive history that would have prompted
neurological or radiological evaluation.
but, at the same time, misleading clue as to its etiology.
This connection has not been reported with other dysto-
nias. In the present study, 21% of patients who had such
a stress exhibited a strong correlation with the onset of
dysphonia. Ginsberg et al.33 also recognized this associa-
tion. In a German study of 18 patients with spasmodic
dysphonia, the authors noted a prevalence of stress within
a 2-year period of symptom onset.34 Standard psychomet-
ric testing failed to show deviation from standardized
norms indicating no underlying psychopathology. Because
the type of stress is individual and subjective, it is difficult
to measure qualitatively or quantitatively. A review of the
literature revealed no published reports of an association
between Diagnostic and Statistical Manual, Fourth Edi-
tion, axis I disorders, such as major depressive disorders,
brief reactive psychosis, or post-traumatic stress disorder,
and spasmodic dysphonia. Although stress may play a role
in the development of spasmodic dysphonia, it does not
appear to be an independent risk factor.
One possible model for stress-related central disor-
ders is attributable to the plasticity of the central nervous
system. Dauer et al.35 theorized that painful stimuli cause
synaptic changes in the basal ganglia where they are
received and processed, leading to the development of
dystonia. A similar mechanism has been postulated in the
pathogenesis of writer’s cramp. Bara-Jimenez et al.36
demonstrated abnormal finger representation in the so-
matosensory (S1) cortex of dystonic patients. This suppo-
sition followed animal studies in which repetitive periph-
eral sensory stimulation and movements induced plastic
changes in the animals’ S1 cortex37; the authors further
postulated that this condition may potentially be treatable
by reordering the S1 representational areas of the affected
organ.38
CONCLUSION
We found a 79% female predominance in spasmodic
dysphonia, as well as an association with writer’s cramp
and essential tremor. There was a strong correlation be-
tween psychological stress and onset of the disorder. In
addition, there was a significantly higher incidence of
measles and mumps in our patient population than in a
similar age group in the general population. There was no
familial or apparent environmental association in the de-
velopment of spasmodic dysphonia. The incidence of ill-
ness and injury in patients with spasmodic dysphonia was
well within confidence intervals of that of the general
population.
The epidemiology of spasmodic dysphonia is similar
in many respects to other dystonias. Although frequently
associated with specific causes and events, ultimately, the
etiology is most likely multifactorial. The future applica-
tion of knowledge of other well-studied diseases may fur-
ther our understanding of spasmodic dysphonia, as well as
provide new directions for future research.
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