parkinson disease ( pd ) is a neurodegenerative disease which its prevalence varies by location and ethnicity ( 1 , 2 ) . the correlation between depression and parkinson disease has remained unclear among iranian population .
the roles of demographic and disease - related variables are not fully described in the association between depression and pd .
depression is highly prevalent among patients with parkinson disease ( 3 , 4 ) and has been demonstrated to reduce quality of life among affected individuals ( 5 , 6 ) .
factors like male gender ( 7 ) , cognitive impairment ( 8) , motor symptoms ( left - sided onset tremor ) ( 9 ) , and impulsivity ( 10 ) are shown to be associated with higher risk of developing depression among patients with pd .
studies have demonstrated that the association between depression and parkinson disease is not merely a reaction to chronic disease , but a consequence of the neurodegenerative process ( 11 , 12 ) . therefore , multifactorial disease - related variables along with non - pd specific components may affect the prevalence of depression in parkinson disease ( 13 ) .
the prevalence of depression and related variables has not yet been described among iranian patients with pd living in kermanshah province . since depression disruptively
affect quality of life among patients with pd , determination of its prevalence and appropriate treatment are essential .
there is some evidence indicating that depression has been underdiagnosed and undertreated in patients with pd ( 14 ) .
studies have shown that depression in pd is more commonly accompanied with somatic and cognitive symptoms ( 15 , 16 ) which may contribute to complexity and underdiagnoses of depression among this population .
determination of predictive factors for depression may help clinicians to cautiously consider susceptible patients for treatment .
in this investigation , the prevalence of depression and the effect of demographic and disease - related variables were assessed in patients with pd living in kermanshah province , iran .
patients with confirmed parkinson disease who were referred to clinics of kermanshah university of medical sciences were invited to participate in this cross - sectional study .
exclusion criteria were as follows : history of depression or other psychiatric disorders before onset of pd , existence of other chronic medical conditions , including cancer , endocrinology disease , coronary vascular disease , history of myocardial infarct , and spinal cord injury .
patients under treatment with special medications such as glucocorticoid , thyroid hormones , anticonvulsive drugs , heparin , lithium , blood glucose reducing agents , and atorvastatin were also excluded .
those with the history of smoking , alcohol , or drug abuse were excluded as well .
participation was voluntarily and patients were assured about the confidentiality of their information . during interviews , private locations were provided to respect patient privacy .
although an assistant was present at the interviews , the final judgements of subjective assessment of depression were indexed according to the psychologist s interpretations .
patients age , gender , educational level , daily medication treatment schedules were asked directly from each individual and indexed in prepared forms during interviews .
pd - related variables , including tremor , rigidity , impaired posture , loss of autonomic movement , mask face , speech and writing changes , excessive salvia , and urinary urgency were examined by a neurologist and also indexed .
the farsi version of snaith - hamilton pleasure scale has 14 items and each of the items has a set of 5 response categories ( definitely agree , agree , no idea , disagree , and strongly disagree ) which are scored from 1 to 5 .
1 ) i would enjoy my favorite television or radio program , 2 ) i would enjoy being with family or close friends , 3 ) i would find pleasure in my hobbies and pastimes , 4 ) i would be able to enjoy my favorite meal , 5 ) i would enjoy a warm bath or refreshing shower , 6 ) i would find pleasure in the scent of flowers or the smell of a fresh sea breeze or freshly baked bread , 7 ) i would enjoy seeing other people s smiling faces , 8) i would enjoy looking smart when i have made an effort with my appearance , 9 ) i would enjoy reading a book , magazine , or newspaper , 10 ) i would enjoy a cup of tea or coffee or my favorite drink , 11 ) i would find pleasure in small things ; e.g. ,
bright sunny day , telephone call from a friend , 12 ) i would be able to enjoy a beautiful landscape or view , 13 ) i would get pleasure from helping others , and 14 ) i would feel pleasure when i receive praise from other people ( 18 ) .
these items cover 4 domains of hedonic experience : interest / pastimes , social interaction , sensory experience , and food / drink .
studies have demonstrated that snaith - hamilton pleasure scale has an internal consistency of 0.91 which shows its validity and reliability to assess hedonic capacity ( 19 ) .
beck depression inventory - ii consists of 21 items and the score ranges from 0 to 63 .
interpretations of the scores are as follows : 1 - 10 , normal ; 11 - 16 , mild mood disturbance ; 17 -2 0 , borderline clinical depression ; 21 - 30 , moderate depressive mood ; 31 - 40 , severe depressive mood ; and over 40 , extreme depression ( 20 ) . the persian version of bdi - ii has been shown to have acceptable internal consistency ( cronbach  = 0.87 ) and test - retest reliability ( r = 0.74 ) ( 21 ) .
bdi - ii was checked to be a valid and reliable instrument to assess depression among patients with parkinson disease ( 22 ) . because a weak association between diabetes mellitus
type 2 and depression has been reported , the history of diabetes in all patients were recorded and blood samples were taken to measure fasting plasma glucose ( fpg ) .
cochran s formula was used to estimate sample size . according to sadeghirad et al .
( 23 ) , the approximate prevalence of major depression in iran is 4.1% . by considering the total population of kermanshah which is about 2000000 , the approximate number of major depression in kermanshah is estimated to be 82000 . using cochran s sample size formula with a margin of error of 5% and confidence interval of 95 ,
the formula was as follows : similar sample size was determined using morgan s table .
we interviewed 412 patients with pd and 62 subjects were excluded according to exclusion criteria .
finally , a total of 350 patients participated in this study which is close to estimated sample size .
all statistical analysis was performed using spss software version 21 ( ibm corporation , usa ) .
categorical variables were described by numbers and percentages whereas continuous variables by mean and standard deviation .
comparison of means between groups was done by t test and 1-way analysis of variance ( anova ) .
patients with confirmed parkinson disease who were referred to clinics of kermanshah university of medical sciences were invited to participate in this cross - sectional study .
exclusion criteria were as follows : history of depression or other psychiatric disorders before onset of pd , existence of other chronic medical conditions , including cancer , endocrinology disease , coronary vascular disease , history of myocardial infarct , and spinal cord injury .
patients under treatment with special medications such as glucocorticoid , thyroid hormones , anticonvulsive drugs , heparin , lithium , blood glucose reducing agents , and atorvastatin were also excluded .
those with the history of smoking , alcohol , or drug abuse were excluded as well .
participation was voluntarily and patients were assured about the confidentiality of their information . during interviews , private locations were provided to respect patient privacy .
although an assistant was present at the interviews , the final judgements of subjective assessment of depression were indexed according to the psychologist s interpretations .
patients age , gender , educational level , daily medication treatment schedules were asked directly from each individual and indexed in prepared forms during interviews .
pd - related variables , including tremor , rigidity , impaired posture , loss of autonomic movement , mask face , speech and writing changes , excessive salvia , and urinary urgency were examined by a neurologist and also indexed .
the farsi version of snaith - hamilton pleasure scale has 14 items and each of the items has a set of 5 response categories ( definitely agree , agree , no idea , disagree , and strongly disagree ) which are scored from 1 to 5 .
1 ) i would enjoy my favorite television or radio program , 2 ) i would enjoy being with family or close friends , 3 ) i would find pleasure in my hobbies and pastimes , 4 ) i would be able to enjoy my favorite meal , 5 ) i would enjoy a warm bath or refreshing shower , 6 ) i would find pleasure in the scent of flowers or the smell of a fresh sea breeze or freshly baked bread , 7 ) i would enjoy seeing other people s smiling faces , 8) i would enjoy looking smart when i have made an effort with my appearance , 9 ) i would enjoy reading a book , magazine , or newspaper , 10 ) i would enjoy a cup of tea or coffee or my favorite drink , 11 ) i would find pleasure in small things ; e.g. , bright sunny day , telephone call from a friend , 12 ) i would be able to enjoy a beautiful landscape or view , 13 ) i would get pleasure from helping others , and 14 ) i would feel pleasure when i receive praise from other people ( 18 ) .
these items cover 4 domains of hedonic experience : interest / pastimes , social interaction , sensory experience , and food / drink .
studies have demonstrated that snaith - hamilton pleasure scale has an internal consistency of 0.91 which shows its validity and reliability to assess hedonic capacity ( 19 ) .
beck depression inventory - ii consists of 21 items and the score ranges from 0 to 63 .
higher scores indicate more severe depressive moods . interpretations of the scores are as follows : 1 - 10 , normal ; 11 - 16 , mild mood disturbance ; 17 -2 0 , borderline clinical depression ; 21 - 30 , moderate depressive mood ; 31 - 40 , severe depressive mood ; and over 40 , extreme depression ( 20 ) . the persian version of bdi - ii has been shown to have acceptable internal consistency ( cronbach  = 0.87 ) and test - retest reliability ( r = 0.74 ) ( 21 ) .
bdi - ii was checked to be a valid and reliable instrument to assess depression among patients with parkinson disease ( 22 ) .
because a weak association between diabetes mellitus type 2 and depression has been reported , the history of diabetes in all patients were recorded and blood samples were taken to measure fasting plasma glucose ( fpg ) .
et al . ( 23 ) , the approximate prevalence of major depression in iran is 4.1% . by considering the total population of kermanshah which is about 2000000 , the approximate number of major depression in kermanshah is estimated to be 82000 . using cochran s sample size formula with a margin of error of 5% and confidence interval of 95 ,
the formula was as follows : similar sample size was determined using morgan s table .
we interviewed 412 patients with pd and 62 subjects were excluded according to exclusion criteria .
finally , a total of 350 patients participated in this study which is close to estimated sample size .
all statistical analysis was performed using spss software version 21 ( ibm corporation , usa ) .
categorical variables were described by numbers and percentages whereas continuous variables by mean and standard deviation .
comparison of means between groups was done by t test and 1-way analysis of variance ( anova ) .
a total of 412 patients selected based on inclusion criteria were interviewed and 62 subjects were excluded according to exclusion criteria . finally , 350 patients ( 52.9% men and 47.1% women ) participated in this investigation .
mean age of the study sample and mean age by the time of pd onset were 64.07  5.08 and 58.46  4.47 years , respectively .
the majority of patients were illiterate ( n = 183 , 52.3% ) and only 4.6% of participants had higher education . tremor was observed in 325 ( 92.9% ) patients and rigidity was detected in 291 ( 83.1% ) patients .
impaired posture , loss of autonomic movements , changes in speech and handwriting were found in 217 ( 62.0% ) , 256 ( 73.1% ) , 217 ( 62.0% ) , and 163 ( 46.6% ) patients , respectively .
only 10.6% of the patients had hyposmia whereas other pd - related variables , including masked face , excessive salvia , and urinary urgency were detected in a higher proportion of patients ( 55.7% , 48% , and 41.1% , respectively ) .
anhedonia was assessed by farsi version of snaith - hamilton pleasure scale , which determines hedonic tone in 4 domains .
obtained scores in each domain were as follows : interest / pastimes ( 7.89  2.01 ) , social interaction ( 14.0  3.94 ) , sensory experience ( 11.53  3.39 ) , food / drink ( 5.47  1.93 ) ( table 1 ) .
female patients were significantly more susceptible to severe and profound depression ( p < 0.0001 ) .
high school educational level and academic educations were related to higher incidence of profound depression ( p < 0.0001 ) , whereas 12.5% of illiterate patients and 14.3% of patients with primary educational level had normal mood .
patients with familial history of pd experienced more severe depression ( p = 0.019 ) . surprisingly
, 40% of patients without tremor had profound depression whereas only 22.7% of individuals with tremor suffered from profound depression ( p = 0.004 ) . however , since only 7.1% of patients did not demonstrate tremor as a pd clinical sign , results on tremor should be interpreted cautiously .
rigidity was also a determinant of increased risk of depression ( p < 0.0001 ) .
similarly , patients with impaired posture were more likely to have profound depression whereas those with intact posture most commonly experienced borderline clinical depression .
furthermore , changes in speech and handwritings were not determinants of depression ( p = 0.095 and 0.062 , respectively ) .
profound depression was detected among 40% of patients with masked face whereas only 5% of individuals without masked face showed profound depressive mood .
this finding demonstrates that masked face is a significant determinant of depression among patients with pd ( p < 0.0001 ) .
hyposmia was also related to higher susceptibility to depression and 50% of patients with hyposmia experienced profound depression ( p = 0.001 ) ( table 2 ) . abbreviation : pd : parkinson disease .
patients with diabetes mellitus type 2 ( dm ii ) were more likely to have mild disturbed mood compared with those individuals without history of dm ii ( 25.7% vs. 6.7% ; p < 0.0001 ) .
similarly , patients with mild disturbed mood had the highest mean value for fpg ( p = 0.007 ) .  
mean age of the patients with mild mood disturbance was low compared to other groups ( p < 0.0001 ) .
lower scores of all domains of farsi version of snaith - hamilton pleasure scale were related to more severe depression ( p < 0.0001 for all subscales ) ( table 3 ) .
p values stand for 1-way analysis of variance ( anova ) for comparison of means between groups .
forty - three patients ( 12.3% ) had normal mood ; however , mild disturbance mood was detected in 36 ( 10.3% ) patients ; 70 ( 20.0% ) patients experienced borderline clinical depression ; and 47 ( 13.4% ) patients had moderate depression .
severe and profound depression was detected in 70 ( 20.0% ) and 84 ( 24.0% ) patients .
the overall estimation of prevalence of severe and profound depression among iranian individuals with pd was 44% .
although the association between depression and parkinson disease ( pd ) has been described ( 11 , 12 ) , the role of pd - related variables on the severity of depression is yet unclear .
( 8) demonstrated that increased severity of pd is associated with higher susceptibility to depression . in the present study , we assessed pd - related variables , including clinical features to identify major determinants of depression among iranian individuals with pd .
our results show that rigidity , impaired posture , masked face , and hyposmia are commonly related to more severe depression .
anhedonia assessed by farsi version of snaith - hamilton pleasure scale was also a major determinant of depression .
( 24 ) showed that prevalence of major depression among patients with pd is about 8.1% .
estimation of prevalence of depression in patients with pd varies among different populations according to study methodology , assessment tool , and community characteristics ( 24 ) .
our estimation of depression prevalence among iranian patients with pd in kermanshah province is about 44% .
using different assessment instrument to assess depression may also contribute to different estimations of depression prevalence in patients with pd . in this regard , williams et al .
( 25 ) compared scales for detection of depression in patients with pd ( beck depression inventory - ii , center for epidemiologic studies depression rating scale - revised , 30-item geriatric depression scale , inventory of depressive symptoms - patient , patient health questionnaire-9 , and unified parkinson disease rating scale - part i ) .
their results showed that all mentioned instruments , except for the unified parkinson disease rating scale - part i , were valid screening tools ( 25 ) .
however , it seems that proper comparison of depression among nations requires utilization of similar methods .
our results demonstrated impaired posture as a determinant of depression . among pd - related variables ,
hassan et al . ( 26 ) showed that postural instability was correlated with depression among patients with pd which was in line with our findings .
furthermore , letvinenko et al . ( 27 ) showed that back pain was correlated with the extent of posture disturbances . since the relationship between pain and depression is also well - documented ( 27 ) , we concluded that impaired posture increases the risk of depression through raising the level of pain . according to recent ninds recommendation ( 28 ) , anhedonia is a specific component of depression in pd .
our study illustrates that anhedonia is significantly correlated with more severe depression among patients with pd which is consistent with ninds recommendations ( 28 ) .
similarly , the close relationship between anhedonia and depression has been reported in general population ( 29 ) and in adolescents with major depression disease ( 30 ) .
this evidence , in line with our study , supports the predictive value of anhedonia in determining depression . on the other hand , there is evidence demonstrating weak discriminating value of anhedonia compared to negative affect and apathy in determining depression in patients with pd ( 16 , 31 ) . in the present study , apathy was not assessed and further investigations are required to compare the discriminating value of apathy and anhedonia as determinants of depression in iranian population with pd in kermanshah .
studies have shown that involvement of ventral striatum and prefrontal cortical regions may contribute to the development of anhedonia in depression ( 32 ) .
deficits in dopamine generating cells in the substantia nigra of the brain are the underlying pathophysiology of pd .
further studies are required to determine whether coincidental involvement of ventral striatum and substantia nigra in pd results in anhedonia among affected individuals .
our investigation showed that women with pd are more susceptible to major depression compared to men which is contrary to the results of hsu et al .
( 33 ) reported that depression is more prominent among women with pd in the united kingdom which supports our results . since multifactorial components , including community characteristics should be considered when addressing depression based on gender distribution , further investigations with controlling social and environmental factors are required to clarify the role of gender in the incidence of depression among iranian people with pd .
some studies have demonstrated the association of depression with diabetes mellitus ( 34 - 37 ) .
however , riederer et al . ( 38 ) showed the association between depression and diabetes mellitus ( dm ) is relatively week among patients with pd .
our study did not approve higher severity of depression in patients with coexistence of pd and diabetes .
these findings show that dm and fpg may not be direct determinant of depression in pd but they have predictive value in determining a specific subgroup of mild depressive mood .
identification of these variables can help give priorities to each patient based on their vulnerability to depression which is the strong point of this study .
however , the weak point of this study is the lack of follow - up process .
therefore , patients could not be assessed with regard to changes in depressive mood through time . in this study ,
the prevalence of depression among iranian patients with pd in kermanshah province and the association between depression severity and pd - related variables were assessed .
it is estimated that 44% of patients with pd suffer from severe and profound depression .
major determinants of depression were female gender , rigidity , impaired posture , masked face , hyposmia , and anhedonia .
 background : the factors affecting the correlation between parkinson disease ( pd ) and depression have remained unclear.objectives:we assessed the prevalence of depression among patients with pd and the association between pd - related variables and depression severity.patients and methods : this is a cross - sectional study performed in kermanshah province of iran . 
 sampling was based on recruitment of subjects according to inclusion and exclusion criteria . 
 patients with confirmed parkinson disease who were referred to clinics of kermanshah university of medical sciences participated in this study . 
 depression was evaluated with beck depression inventory - ii ( bdi - ii ) . 
 clinical characteristics of pd , including tremor , rigidity , impaired posture , loss of autonomic movement , changes in speech and handwriting , masked face , and hyposmia were indexed . 
 anhedonia was assessed with farsi version of snaith - hamilton pleasure scale . 
 data were collected between april 2010 and march 2014.results:a total of 350 patients ( 52.9% men and 47.1% women ) participated in this investigation . 
 female gender ( 36.5% in women vs. 13.0% in men , p < 0.0001 ) , impaired posture ( 27.2% in affected individuals vs. 18.8% , p = 0.002 ) , masked face ( 39.0% vs. 5.2% , p < 0.0001 ) , and hyposmia ( 48.7% vs. 21.0% , p = 0.001 ) were associated with higher susceptibility to profound depression . 
 lower scores of all domains of farsi version of snaith - hamilton pleasure scale ( including interest / pastimes , social interaction , sensory experience , and food / drink ) were related to more severe depression ( p < 0.0001 for all subscales ) . 
 severe and profound depression was found in 44% of the participants.conclusions:this study estimated that the prevalence of major depression among iranian individuals with pd living in kermanshah as 44% . 
 major determinants of depression were female gender , rigidity , impaired posture , masked face , hyposmia , and anhedonia . 
1. Background
2. Objectives
3. Patients and Methods
3.1. Study Design and Participants
3.2. Demographics and Parkinson Disease-Related Variables
3.3. Beck Depression Inventory-II (BDI-II)
3.4. Laboratory Measurements
3.5. Sample Size Estimation
3.6. Statistical Analysis
4. Results
5. Discussion