Table 1.
Main characteristics of the cohort studies included in the meta-analysis.
| Li et al. (13) | Chen et al. (14) | |
|---|---|---|
| Country | Sweden | Taiwan |
| Study design | Retrospective cohort | Retrospective cohort |
| Year of publication | 2011 | 2020 |
| Main finding(s) | Hypothyroidism is associated with an increased risk of PD. Hyperthyroidism is associated with an increased risk of PD. |
Hypothyroidism is associated with an increased risk of PD. |
| Total number of participants | Total: 310,552 Patients with hyperthyroidism: 34,735 Patients without hyperthyroidism: 275,817 Patients with hypothyroidism: 8,703 Patients without hypothyroidism: 301,849 |
Patients with hypothyroidism: 4,725 Comparators: 4,725 |
| Recruitment of participants | Patients with hypo/hyperthyroidism were identified from the MigMed database located at the Center for Primary Health Care Research, Lund University from 1964 to 2007 Comparators without hypo/hyperthyroidism were identified from the same database. |
Patients diagnosed with hypothyroidism between 2000 and 2012 were identified from the 2000 Longitudinal Health Insurance Database which contained claim data and registration files of both ambulatory and inpatient care of one million individuals randomly sampled from the Taiwan National Health Insurance Research Database between 1995 and 2013. Comparators without hypothyroidism were identified from the same database. Comparators were matched to cases by age, sex, index year, and CCI score. |
| Diagnosis of hypo/hyperthyroidism | Hyperthyroidism: Presence of diagnostic codes for Hashimoto/hypothyroidism (ICD-7: 253; ICD-8: 245.1, 243, 244; ICD-9: 245C, 243, 244; ICD-10: E00-03, E06.3) Hyperthyroidism: Presence of diagnostic codes for Graves/hyperthyroidism (ICD-7: 252; ICD-8: 242; ICD-9: 242; ICD-10: E05) in the database |
Presence of diagnostic codes for hypothyroidism in the database (ICD-9-CM: 243, 244) |
| Diagnosis of PD | Presence of diagnostic codes for PD in the database (ICD-7: 350; ICD-8: 342.0; ICD-9: 332; ICD-10: G20-21) | Presence of diagnostic code for PD in the database (ICD-9-CM: 332) |
| Follow-up period | Until the development of PD, death, emigration or closing date (December 31st, 2007) | Until the development of PD, removal from the National Health Insurance Program of Taiwan, death or the end of 2013 |
| Average duration of follow-up (years) | Patients with hypo/hyperthyroidism: N/A Comparators: N/A |
Patients with hypothyroidism: 7.1 Comparators: 7.1 |
| Average age of participants at index date (years) | Patients with hypo/hyperthyroidism: N/A Comparators: N/A |
Patients with hypothyroidism: N/A Comparators: N/A |
| Percentage of female | Patients with hypo/hyperthyroidism: N/A Comparators: N/A |
Patients with hypothyroidism: 81.5 Comparators: 81.5 |
| Variables adjusted in multivariate analysis | Age, study period, socioeconomic status, region of residence, hospitalization of COPD and hospitalization of alcoholism/alcohol-related liver disease |
Age, sex, CCI score, comorbidities and duration of levothyroxine use |
| Comorbidities | N/A | Patients with hypothyroidism: CCI score 0: 75.7%; CCI 1-2: 18.3%; CCI ≥3: 6.0%; brain injury: 4.6%; CVD: 7.9%; HT: 10.5%; dyslipidemia: 19.8%; DM: 12.7% Comparators: CCI score 0: 75.7%; CCI 1-2: 18.3%; CCI ≥3: 6.0%; brain injury: 3.5%; CVD: 6.7%; HT: 10.6%; dyslipidemia: 12.2%; DM: 9.8% |
| Newcastle-Ottawa score | Selection: 4 Comparability: 2 Outcome: 3 |
Selection: 4 Comparability: 2 Outcome: 3 |
| Lin et al. ( 15 ) | ||
| Country | Taiwan | |
| Study design | Retrospective cohort | |
| Year of publication | 2021 | |
| Main finding(s) | Hyperthyroidism is associated with an increased risk of PD. | |
| Total number of participants | Patients with hyperthyroidism: 8,788 Patients without hyperthyroidism: 8,788 |
|
| Recruitment of participants | Patients diagnosed with hyperthyroidism between 2000 and 2012 were identified from the 2000 Longitudinal Health Insurance Database which contained claim data and registration files of both ambulatory and inpatient care of one million individuals randomly sampled from the Taiwan National Health Insurance Research Database between 1995 and 2013. Comparators without hyperthyroidism were identified from the same database. Comparators were matched to cases by age, sex, index year, and CCI score. |
|
| Diagnosis of hypo/hyperthyroidism | Presence of diagnostic codes for hypothyroidism in the database (ICD-9-CM: 242) | |
| Diagnosis of PD | Presence of diagnostic code for PD in the database (ICD-9-CM: 332) | |
| Follow-up period | Until the development of PD, removal from the National Health Insurance Program of Taiwan, death or the end of 2013 | |
| Average duration of follow-up (years) | Patients with hypothyroidism: 8.0 Comparators: 8.0 |
|
| Average age of participants at index date (years) | Patients with hypothyroidism: N/A Comparators: N/A |
|
| Percentage of female | Patients with hypothyroidism: 76.8 Comparators: 76.8 |
|
| Variables adjusted in multivariate analysis | Age, sex, CCI score, comorbidities and antithyroid therapy | |
| Comorbidities | Patients with hyperthyroidism: CCI score 0: 91.9%; CCI 1-2: 6.7%; CCI ≥3: 1.4%; brain injury: 3.8%; CVD: 4.6%; HT: 13.8%; dyslipidemia: 15.5%; DM: 13.1% Comparators: CCI score 0: 91.9%; CCI 1-2: 6.7%; CCI ≥3: 1.4%; brain injury: 3.7%; CVD: 4.1%; HT: 11.0%; dyslipidemia: 10.2%; DM: 7.8% |
|
| Newcastle-Ottawa score | Selection: 4 Comparability: 2 Outcome: 3 |
CCI, Charlson Comorbidity Index; CVD, Cerebrovascular disease; DM, Diabetes mellitus; HT, Hypertension; ICD-7, The International Classification of Disease, 7th Revision; ICD-8, The International Classification of Disease, 8th Revision; ICD-9, The International Classification of Disease, 9th Revision; ICD-9-CM, The International Classification of Disease, 9th Revision, Clinical Modification; ICD-10, The International Classification of Disease, 10th Revision; N/A, Not available; PD, Parkinson’s disease.