Abstract

Background.

Timely diagnosis of Parkinson’s disease (PD), facilitating early intervention, depends largely on the GP’s awareness of early symptomatology. For general practice, it is unknown which prodromal symptoms (symptoms preceding the typical motor symptoms of PD) demand the GP’s alertness.

Objective.

To assess prodromal symptoms that should alert the GP to the possibility of PD in primary care patients.

Methods.

A nested case-control study was carried out in a population of approximately 12000 patients registered in the Continuous Morbidity Registration database affiliated with the University of Nijmegen in the Netherlands. The database pools subject data from four primary care practices. The subjects comprised all 86 patients diagnosed with PD between 1972 and 2007, and 78 controls, matched by sex, age, socioeconomic status and primary care practice. The primary measures of outcome were the prodromal symptoms presenting in the two years prior to the diagnosis of PD. The number (and type) of referrals and diagnostic tests were also assessed.

Results.

In the two-year period prior to diagnosis, PD patients more often presented with functional somatic symptoms, constipation, hyperhidrosis and sleep disorders than controls. Patients also more frequently experienced more than one prodromal symptom and were more often referred within the primary care team or to a medical specialist.

Conclusions.

Prodromal symptoms of PD are encountered in general practice. GPs should be alert when patients present with multiple prodromal symptoms in a two-year period, especially considering the benefits of early intervention, and the future possibilities for disease-modifying therapy.

Introduction

Parkinson’s disease (PD) is a common neurodegenerative disorder that has a severe impact on the patient’s daily life (1). Multiple caregivers are involved in the course of the disease (2). The diagnosis of PD requires the presence of bradykinesia, combined with other motor symptoms such as muscular rigidity, a 4–6 Hz resting tremor or postural instability (UK Brain Bank Clinical Diagnostic Criteria (3)). However, it is becoming clear that non-motor symptoms such as autonomic dysfunction, depression, anxiety and cognitive decline are also part of the PD symptom complex (4–6). Moreover, some motor and non-motor symptoms, including olfactory dysfunction and rapid eye movement (REM) sleep behaviour disorder are prodromal symptoms; symptoms that are already present before the onset of the typical motor signs of PD (4–7). Patients seem to be hindered by individual prodromal symptoms or combinations of them (8,9) as they consult GPs and medical specialists with increasing frequency in the 10-year period before they are diagnosed with PD (9).

Recognition of prodromal symptoms and increase in consultation frequency are essential for timely referral and early intervention, aiming to maintain the best quality of life for patients with PD (3,10–12). GPs play an important role in this, as patients will generally first present their symptoms to their GP, and not, for example, to a neurologist. Knowledge and awareness of the prodromal symptoms of PD are therefore crucial for GPs (6).

Earlier studies of prodromal symtoms are mainly hospital based and focus on patients referred to neurologists (4,5,7,13); only few studies are performed focussing on the population typically presented to a GP (9). An Australian study showed there are deficits in the GP’s knowledge of motor and non-motor aspects of PD. Knowledge of the prodromal symptoms of PD was not assessed (14). However, given the low prevalence of PD in individual family practices, it seems likely that there are also deficiencies in the GP’s knowledge of the prodromal symptoms.

This study therefore aims to characterize the prodromal symptoms of PD presenting in general practice and to give insight into referral rates in the 2 years prior to the diagnosis, in order to increase the GP’s alertness for symptoms of PD.

Methods

Continuous Morbidity Registration database

We conducted a nested case-control study using data from the Continuous Morbidity Registration (CMR) database affiliated with the University of Nijmegen in the Netherlands. The recording in the database is anchored in the Dutch healthcare system where all citizens are registered with a personal GP, whether they consult the GP or not. Since 1971, all health problems are monitored in a population of approximately 12000 patients from four general practices, representative of the Dutch population with regard to age and sex. In addition to health problems, sex, age, socioeconomic status (SES; low, middle and high) and marital status are registered (15,16).

All episodes of illness seen by or reported to the GP are registered as soon as they are established, using an adapted version of the E-list (17). Monthly meetings are held with all participating GPs to discuss classification problems, monitor the application of diagnostic criteria and discuss coding problems in real and hypothetical cases. When necessary, diagnoses and codes are corrected. The validity of the CMR has been established repeatedly (15) and more than 65 papers based on CMR data have been published in international peer-reviewed journals between 1992 and 2012 (16).

Patients with PD

We selected all patients from the CMR database who were diagnosed with PD between 1972 and 2007. From 1972 to 1980, PD was diagnosed by a GP and from 1980 to 2007, by a neurologist. Patients must have been registered with the general practice for at least 2 years before their diagnosis. For a 2-year period prior to the diagnosis, the following variables were collected: sociodemographic characteristics; data on four major co-morbid conditions (diabetes mellitus, cardiovascular diseases, COPD, rheumatoid arthritis); prodromal symptoms; and data on referrals and diagnostic tests. Based on a literature study, a selection of prodromal symptoms was studied: functional somatic complaints; (autonomic) dysfunction, such as constipation, hyperhidrosis, orthostatic hypotension, urinary incontinence, swallowing difficulty and sleep disorders; musculoskeletal complaints; neuropsychiatric disorders, such as anxiety, dementia and depression; olfactory dysfunction; and traumata, such as fractures, luxations and distorsions (4,5,7–9,13). Functional somatic symptoms were defined as physical symptoms, appearing in patients with presumed psychosocial problems or psychological distress, that remain medically unexplained after adequate examination (18).

Referrals were divided into three categories: somatic within the primary care team (physical therapist, social worker, occupational health officer, speech therapist, dietician and district nurse), somatic medical (all medical specialists except for a psychiatrist) and mental health (psychiatrist, psychologist and ambulatory mental health care). Diagnostic tests included hematological tests, X-ray examinations and ultrasonography.

Data on prodromal symptoms were obtained directly from the medical records, except for data on clear diagnoses and information about referrals and diagnostic tests. These data were derived from the CMR database. A patient was assumed to experience a prodromal symptom when a note was made in the medical record or when a diagnosis was coded in the database.

Controls

For each patient with PD, a matched control was drawn from the CMR population. The control matched the patient in sex, age, SES and primary care practice at the date the patient was diagnosed with PD. Furthermore, the match must have been registered at the same practice as the patient for a minimum of 2 years. The only exclusion criterion in the control group was the diagnosis of PD. For controls, the same information as described for patients with PD was obtained.

Statistical methods

Statistical analyses were conducted using SPSS 20. Descriptive statistics were calculated. The chi-square test was used to assess the relationship between PD and the presence of the selected co-morbid conditions. Conditional logistic regression was used in this nested case-control study to investigate the relationship between PD and the prodromal symptoms. The criteria for the matched sets were sex, age category (≤69 years, 70–80 years, ≥81 years), SES and practice. The numbers of cases and controls in the matched sets were uneven. In case a prodromal symptom did not present in the control group, a Fisher’s exact test was used. In order to reveal patterns in the combined presentation of prodromal symptoms, all presented combinations of prodromal symptoms were scored. The chi-square test was used to assess the relationship between PD and the number of prodromal symptoms presented. Conditional logistic regression was used to investigate the relationship between PD and the number of referrals and diagnostic tests. The criteria for the matched sets were sex, age category (≤69 years, 70–80 years, ≥81 years), SES and practice. The number of referrals and diagnostic tests were divided into categories of frequency (0, 1, ≥2). There were varying numbers of cases and controls in the matched sets. The chi-square test was used to explore the relationship between PD and the number of referrals and diagnostic tests per individual (categories: 0, 1, ≥2).

A P-value less than 0.05 was considered statistically significant.

Results

Characteristics of subjects

We included 86 consecutive patients with PD and 78 controls (Table 1). There were no suitable controls for eight patients. The patient group consisted of 57% men, the mean age was 72.3 years (SD 8.8). Patients were of low, medium and high SES in 44.2%, 50.0% and 5.8% of the cases, respectively. Significantly more PD patients than controls had a cardiovascular disease (P 0.018; Table 1).

Table 1.

Characteristics of patients with Parkinson’s disease and matched controls

Characteristics Patients (n = 86) Controls (n = 78) P-value 
Sex (% male) 49 (57.0%) 42 (53.8%)  
Mean age (years) 72.3 (SD 8.8) 70.6 (SD 8.9)  
Socioeconomic status 
 Low, n (%) 38 (44.2%) 34 (43.6%)  
 Middle, n (%) 43 (50.0%) 39 (50.0%)  
 High, n (%)   5 (5.8%)   5 (6.4%)  
Co-morbidity 
 Diabetes mellitus, n (%)   8 (9.3%)   4 (5.1%) 0.305 
 Cardiovascular diseases, n (%) 36 (41.9%) 19 (24.4%) 0.018* 
 COPD, n (%) 12 (14.0%)   9 (11.5%) 0.644 
 Rheumatoid arthritis, n (%)   1 (1.2%)   1 (1.3%) 0.945 
Characteristics Patients (n = 86) Controls (n = 78) P-value 
Sex (% male) 49 (57.0%) 42 (53.8%)  
Mean age (years) 72.3 (SD 8.8) 70.6 (SD 8.9)  
Socioeconomic status 
 Low, n (%) 38 (44.2%) 34 (43.6%)  
 Middle, n (%) 43 (50.0%) 39 (50.0%)  
 High, n (%)   5 (5.8%)   5 (6.4%)  
Co-morbidity 
 Diabetes mellitus, n (%)   8 (9.3%)   4 (5.1%) 0.305 
 Cardiovascular diseases, n (%) 36 (41.9%) 19 (24.4%) 0.018* 
 COPD, n (%) 12 (14.0%)   9 (11.5%) 0.644 
 Rheumatoid arthritis, n (%)   1 (1.2%)   1 (1.3%) 0.945 

*P < 0.05, statistically significant.

Prodromal symptoms presented to the GP

Several symptoms presented by PD patients to the GP with higher frequency in the 2 years prior to the diagnosis, compared to matched controls (Table 2). There was a significant difference in functional somatic symptoms (OR 2.45; P 0.014), constipation (OR 3.32; P 0.039) and sleep disorders (OR 6.98; P 0.002) presented. Hyperhidrosis was only reported in the patient group (9.3% versus 0%; P 0.007). For all other symptoms, including musculoskeletal complaints, there was no significant difference between the PD patients and the controls.

Table 2.

Symptoms presented to the GP in the 2 years prior to the diagnosis Parkinson’s disease; patients compared to matched controls

Symptoms Patients (n = 86) Controls (n = 78) OR 95% CI P-value 
Functional somatic symptoms 33 (38.4%) 17 (21.8%) 2.45 1.2–5.1 0.014* 
Autonomic dysfunction: 
 Constipation 16 (18.6%)   4 (5.1%) 3.32 1.1–10.4 0.039* 
 Hyperhidrosis   8 (9.3%)   0 – – 0.007*a 
 Orthostatic hypotension   2 (2.3%)   0 – – 0.498a 
 Urinary incontinence   9 (10.5%)   4 (5.1%) 3.21 0.8–13.2 0.106 
 Swallowing difficulty   4 (4.7%)   1 (1.3%) 2.23 0.2–22.2 0.493 
 Sleep disorders 22 (25.6%)   3 (3.9%) 6.98 2.0–24.3 0.002* 
 Musculoskeletal complaints 51 (59.3%) 37 (47.4%) 1.60 0.8–3.2 0.171 
Neuropsychiatric disorders: 
 Anxiety   0   0 – – – 
 Dementia   2 (2.3%)   2 (2.6%) 0.65 0.1–5.3 0.688 
 Depression   3 (3.5%)   0 – – 0.247a 
 Olfactory dysfunction   1 (1.2%)   0 – – 1.000a 
 Traumata   3 (3.5%)   7(9.0%) 0.33 0.1–1.4 0.123 
Symptoms Patients (n = 86) Controls (n = 78) OR 95% CI P-value 
Functional somatic symptoms 33 (38.4%) 17 (21.8%) 2.45 1.2–5.1 0.014* 
Autonomic dysfunction: 
 Constipation 16 (18.6%)   4 (5.1%) 3.32 1.1–10.4 0.039* 
 Hyperhidrosis   8 (9.3%)   0 – – 0.007*a 
 Orthostatic hypotension   2 (2.3%)   0 – – 0.498a 
 Urinary incontinence   9 (10.5%)   4 (5.1%) 3.21 0.8–13.2 0.106 
 Swallowing difficulty   4 (4.7%)   1 (1.3%) 2.23 0.2–22.2 0.493 
 Sleep disorders 22 (25.6%)   3 (3.9%) 6.98 2.0–24.3 0.002* 
 Musculoskeletal complaints 51 (59.3%) 37 (47.4%) 1.60 0.8–3.2 0.171 
Neuropsychiatric disorders: 
 Anxiety   0   0 – – – 
 Dementia   2 (2.3%)   2 (2.6%) 0.65 0.1–5.3 0.688 
 Depression   3 (3.5%)   0 – – 0.247a 
 Olfactory dysfunction   1 (1.2%)   0 – – 1.000a 
 Traumata   3 (3.5%)   7(9.0%) 0.33 0.1–1.4 0.123 

aP-value Fisher’s exact test.

*P < 0.05, statistically significant.

Of all the PD patients, 53.4% presented with multiple prodromal symptoms in the 2-year period prior to the diagnosis, versus 25.6% of the controls (Fig. 1) (OR 3.37; P < 0.001). We did not find any salient patterns in the combined presentation of prodromal symptoms (results not shown).

Figure 1.

Number of prodromal symptoms presented to the GP in the 2 years prior to the diagnosis Parkinson’s disease; patients compared to matched controls.

Figure 1.

Number of prodromal symptoms presented to the GP in the 2 years prior to the diagnosis Parkinson’s disease; patients compared to matched controls.

Referrals and diagnostic tests

Patients were referred more frequently than controls (Table 3). There was a significant difference in referral within the primary care team (OR 3.28; P 0.007). There was also a significant difference in referrals to a medical specialist; 46.5% of the PD patients were referred to a medical specialist at least once (OR 4.26; P 0.002), compared to 20.5% of the controls (OR 2.69; P 0.088). Referral to a psychologist or psychiatrist was very low.

Table 3.

Number of individuals with 0, 1 or ≥2 referrals or diagnostic tests in the 2 years prior to the diagnosis Parkinson’s disease; patients compared to matched controls

 Patients (n = 86) Controls (n = 78) OR 95% CI P-value 
Referrals 
Somatic within the primary care team 
 0 59 (68.6%) 69 (88.5%)    
 1 23 (26.7%)   9 (11.5%) 3.28 1.4–7.8 0.007* 
 ≥2   4 (4.7%)   0 – – – 
Somatic medical      
 0 46 (53.5%) 62 (79.5%)    
 1 26 (30.2%) 10 (12.8%) 4.26 1.7–10.9 0.002* 
 ≥2 14 (16.3%)   6 (7.7%) 2.69 0.9–8.4 0.088 
Mental health 
 0 77 (98.8%) 85 (98.7%)    
 1   1 (1.2%)   1 (1.3%) – – – 
 ≥2   0   0 – – – 
Diagnostic tests 
 0 37 (43.0%) 46 (59.0%)    
 1 30 (34.9%) 19 (24.4%) 1.94 0.9–4.0 0.077 
 ≥2 19 (22.1%) 13 (16.7%) 1.99 0.8–4.8 0.126 
 Patients (n = 86) Controls (n = 78) OR 95% CI P-value 
Referrals 
Somatic within the primary care team 
 0 59 (68.6%) 69 (88.5%)    
 1 23 (26.7%)   9 (11.5%) 3.28 1.4–7.8 0.007* 
 ≥2   4 (4.7%)   0 – – – 
Somatic medical      
 0 46 (53.5%) 62 (79.5%)    
 1 26 (30.2%) 10 (12.8%) 4.26 1.7–10.9 0.002* 
 ≥2 14 (16.3%)   6 (7.7%) 2.69 0.9–8.4 0.088 
Mental health 
 0 77 (98.8%) 85 (98.7%)    
 1   1 (1.2%)   1 (1.3%) – – – 
 ≥2   0   0 – – – 
Diagnostic tests 
 0 37 (43.0%) 46 (59.0%)    
 1 30 (34.9%) 19 (24.4%) 1.94 0.9–4.0 0.077 
 ≥2 19 (22.1%) 13 (16.7%) 1.99 0.8–4.8 0.126 

*P < 0.05, statistically significant.

More diagnostic tests were performed in the patient group than in the control group, but the results were not statistically significant.

Conclusions

Summary of the main findings

We identified that in primary care, PD patients more frequently experience prodromal symptoms in the 2 years prior to the diagnosis compared to controls. These prodromal symptoms include functional somatic symptoms, constipation, hyperhidrosis and sleep disorders. Over 50% of the PD patients presented more than one prodromal symptom. However, specific combinations of presented prodromal symptoms could not be found.

Referrals within the primary care team and to medical specialists occurred more often in the patient group, whereas referral for mental health was low and comparable to controls. Diagnostic tests were requested equally for PD patients and controls.

Comparison with existing literature

We found that several prodromal symptoms, corresponding with those reported in the literature, were presented to the GP. Studies have shown that autonomic dysfunction and REM sleep behaviour disorder can be present in the prodromal phase of PD (4,5,8,9,19). Although we did not specify the nature of the sleeping disorders studied, it is likely that these included REM sleep behaviour disorder.

Functional somatic symptoms diagnosed in the prodromal phase of PD might in fact be early autonomic symptoms of PD that are misdiagnosed, interpreted and registered by GPs as functional somatic symptoms. However, a recent study suggested a link between the pathophysiology of PD and a higher susceptibility of PD patients to functional somatic symptoms in the course of the disease (20). In our study, functional somatic symptoms were recorded more frequently in PD patients than in controls. It is therefore possible that the higher susceptibility to functional somatic symptoms is already present in the years before PD is diagnosed. Regardless of the reason, GPs should be aware that the presentation of functional somatic symptoms could in fact be the presentation of the prodromal phase of PD.

In contrast to earlier studies (8,9), we did not find a significant difference in musculoskeletal symptoms between PD patients and controls. Since these symptoms already have high prevalence in the age group in which PD is mostly diagnosed, they seem to be of little value for GPs as distinctive signs of early PD.

Although the prodromal symptoms studied may not individually be specific enough to indicate early PD (6), our results show that two or more prodromal symptoms presenting in a 2-year period could be an indicator of early PD.

Our results demonstrating the increased number of referrals in the patient group support results from earlier research (9,11). One study suggested that the increase in referrals reflects the variable non-motor symptoms that may present early or precede the motor phase of PD (11). Our study is in line with this, in that it showed that the increase in referral rate is not solely due to referrals to a neurologist.

Strengths and limitations of the study

The strength of this study is the use of a well-documented database (eliminating the risk of recall bias) to study the symptoms presented to the GP, the referrals and diagnostic tests in a 2-year period before the diagnosis of PD. Another strength is the inclusion of unselected cases of PD, in the early stage of their disease development. The database made it possible to recruit controls from the general population and, as a consequence, the findings hold external validity for PD diagnosis in primary care.

However, some methodological issues merit consideration. First of all, as for every longitudinal research, the number of patients included and the duration of the observation period are inversely proportional to each other. We chose a study period of 2 years prior to the diagnosis of PD, since for this period information could be retrieved for a substantial number of patients and controls. It cannot be excluded that a longer study period would lead to different results.

Secondly, we used a pre-selected list of prodromal symptoms, based on literature (4,5,7–9,13) and supported by expert opinion. Because the main focus of our research was to extend the knowledge of GPs in order to increase their alertness, we studied known prodromal symptoms that were presented in general practice. The pre-selected list of prodromal symptoms was not intended to be comprehensive. It is therefore possible that some symptoms that occur in the early phase of PD, known or unknown at the time, were not included. An interesting target for future research could be identifying novel prodromal symptoms of PD by studying all symptoms presented in general practice by patients later diagnosed with PD.

A third point of attention is that only symptoms registered in the patient’s medical record were included in this study. The results may therefore be an underestimation of the actual prevalence of prodromal symptoms, due to lack of presentation by the patient or lack of reporting by the GP. However, relying on symptoms captured in the medical health record of the patient closely resembles everyday clinical practice. Furthermore, by focussing on these symptoms, the analysis was based on symptoms significant enough for patients to consult and seek help from their GP.

Fourthly, attention needs to be given to the age categories designated for the conditional logistic regression. The age group of ≤69 years may seem too heterogeneous to form one group. However, this group consisted of a range of PD patients aged 52–69 years, with one outlier of 39 years. Since matching was also done by age, the distribution of age in the control group is comparable to the patient group. We therefore believe this heterogeneity has no noteworthy influence on the results.

A fifth point of attention is the possibility of confounding factors. The difference in the number of referrals might be partly explained by the difference in co-morbidity between the group of PD patients and the control group. The presentation of adverse effects of medication could, in some cases, be similar with the presentation of some of the prodromal symptoms studied. Smoking habits and alcohol consumption could have also influenced the results.

Finally, our study did not comprehensively assess the prodromal symptoms of PD in general practice. It is therefore not possible to calculate the predictive values of these symptoms. However, the Dutch CMR database, with its large sample size, longitudinal design and proven validity (15) provided an important insight into the early phase of PD, suggesting that the first disabling symptoms of the disorder can be seen in general practice. Given the relatively low prevalence of PD in general practices, the results of this study can offer valuable support in handling the uncertainty around diagnosis, as is the case for other low-prevalence diseases (21).

In conclusion

Prodromal symptoms are a reality in general practice. The therapeutic benefit of early intervention (3,12) and the future possibilities for disease-modifying therapies, emphasize the importance of recognizing prodromal symptoms of PD leading to early diagnosis. This falls into the primary care domain and the role of GPs: awareness that functional somatic symptoms, constipation, hyperhidrosis, sleep disorders and an increase in referrals may signal PD, leading to an early diagnosis.

Declarations

Funding: none.

Ethical approval: this study was performed according to the Code of Conduct for Health Research, which has been approved by the Data Protection Authorities for conformity with the applicable Dutch privacy legislation.

Conflict of interest: none.

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