The nationwide register-based Finnish Study on Parkinson’s disease register-based FINPARK study includes 22,189 people who received clinically confirmed PD diagnosis during the years 1996–2015 and were community-dwelling at the time of diagnosis.
People with PD diagnosis were identified from the Special Reimbursement Register maintained by the Social Insurance Institution of Finland (SII). Originally, 29,942 people eligible for reimbursement of anti-Parkinson drugs were identified, but as these drugs can also be used for other reasons, we excluded those who did not have ICD-10 code for PD (G20) recorded in the Special Reimbursement Register (n = 1244), those who were < 35 years old at the time of PD diagnosis (N = 53) and those who had diagnoses whose symptoms may be confused with PD (n = 6456) within 2 years of PD diagnosis, which lead to a cohort of 22,189 people. The exclusion diagnoses are listed in Supplementary Table1 . These people were excluded, as diagnosis of PD and its differential diagnostics is challenging, and false diagnoses are common in the early phase [16 (link), 17 (link)]. The proportion of excluded people (25.9%) in our study is within the range of estimated proportion of false diagnoses [16 (link), 17 (link)].
The application for special reimbursement includes anamnesis of the patient and description of the characteristic clinical features of PD including bradykinesia, rigidity and tremor. These applications are centrally reviewed in the SII. Special reimbursement for PD medications is granted if predefined criteria for PD diagnosis are fulfilled and diagnoses must be confirmed by a neurologist. Diagnosis of PD was based on United Kingdom Parkinson’s Disease Society Brain Bank’s criteria [18 (link)].
An age (+/− 1 year), sex and region-matched comparison cohort was identified from the SII database covering all residents. The index date was the date of PD diagnosis for the matched referent. The comparison people were not allowed to have purchases of PD medication (Anatomical Therapeutic Chemical classification ATC code N04) or the reimbursement code ever before the index date or 12 months after and during the diagnosis month of the referent people with PD. They also had to remain alive and community-dwelling during the month of index date. The diagnosis-based exclusion criteria of comparison people was otherwise similar to that of the PD cohort, but dementia due to PD (ICD-10 F02.3) was added to list of exclusion criteria, leaving altogether 148,009 comparison people. Dementia due to PD was added to ensure exclusion of people with PD from the comparison cohort.
Incidence of antidepressant use was investigated from 10 years before to 15 years after the PD diagnosis. Data on antidepressant purchases during 1995–2016 were gathered from the Prescription Register, which contains data on reimbursed medication purchases. Antidepressants were defined as ATC class N06A (Supplementary Table2 ), and further categorized as selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), serotonin–norepinephrine reuptake inhibitors (SNRIs), mirtazapine, and other antidepressants. Incident users were identified with a one-year washout-period, starting 11 years before PD diagnosis. For those diagnosed before or during the year 2005, year 1995 was used as a one-year washout-period. People who purchased antidepressants during the washout period, those who were hospitalised for > 50% of the washout or hospitalised for the last 90 days of washout were excluded (Supplementary Figure 1 ). Only the first initiation of antidepressant use after washout period was included in the analysis. Hospitalisation data were obtained from the Care Register for Health Care.
Data on comorbidities since 1972 until the index date were obtained from the Special Reimbursement register: asthma or chronic obstructive pulmonary disease (code 203), cardiovascular diseases including chronic heart failure (201) hypertension (205), coronary artery disease (206, 213, 280) and rheumatoid arthritis and connective tissue diseases (code 202). Diabetes was defined as special reimbursement code 103 or purchase of antidiabetics (ATC A10, excluding guar gum A10BX01). History of depression (discharge diagnosis or diagnosis in outpatient visit in specialized health care) was identified from the Care Register for Health Care using ICD-82960, 3004, 3011; ICD-9: 2961, 2968, 3011, 3004; ICD-10 F32-F34, F38-F39.
People with PD diagnosis were identified from the Special Reimbursement Register maintained by the Social Insurance Institution of Finland (SII). Originally, 29,942 people eligible for reimbursement of anti-Parkinson drugs were identified, but as these drugs can also be used for other reasons, we excluded those who did not have ICD-10 code for PD (G20) recorded in the Special Reimbursement Register (n = 1244), those who were < 35 years old at the time of PD diagnosis (N = 53) and those who had diagnoses whose symptoms may be confused with PD (n = 6456) within 2 years of PD diagnosis, which lead to a cohort of 22,189 people. The exclusion diagnoses are listed in Supplementary Table
The application for special reimbursement includes anamnesis of the patient and description of the characteristic clinical features of PD including bradykinesia, rigidity and tremor. These applications are centrally reviewed in the SII. Special reimbursement for PD medications is granted if predefined criteria for PD diagnosis are fulfilled and diagnoses must be confirmed by a neurologist. Diagnosis of PD was based on United Kingdom Parkinson’s Disease Society Brain Bank’s criteria [18 (link)].
An age (+/− 1 year), sex and region-matched comparison cohort was identified from the SII database covering all residents. The index date was the date of PD diagnosis for the matched referent. The comparison people were not allowed to have purchases of PD medication (Anatomical Therapeutic Chemical classification ATC code N04) or the reimbursement code ever before the index date or 12 months after and during the diagnosis month of the referent people with PD. They also had to remain alive and community-dwelling during the month of index date. The diagnosis-based exclusion criteria of comparison people was otherwise similar to that of the PD cohort, but dementia due to PD (ICD-10 F02.3) was added to list of exclusion criteria, leaving altogether 148,009 comparison people. Dementia due to PD was added to ensure exclusion of people with PD from the comparison cohort.
Incidence of antidepressant use was investigated from 10 years before to 15 years after the PD diagnosis. Data on antidepressant purchases during 1995–2016 were gathered from the Prescription Register, which contains data on reimbursed medication purchases. Antidepressants were defined as ATC class N06A (Supplementary Table
Data on comorbidities since 1972 until the index date were obtained from the Special Reimbursement register: asthma or chronic obstructive pulmonary disease (code 203), cardiovascular diseases including chronic heart failure (201) hypertension (205), coronary artery disease (206, 213, 280) and rheumatoid arthritis and connective tissue diseases (code 202). Diabetes was defined as special reimbursement code 103 or purchase of antidiabetics (ATC A10, excluding guar gum A10BX01). History of depression (discharge diagnosis or diagnosis in outpatient visit in specialized health care) was identified from the Care Register for Health Care using ICD-82960, 3004, 3011; ICD-9: 2961, 2968, 3011, 3004; ICD-10 F32-F34, F38-F39.
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