Table 1.
Characteristics of included studies.
| References | Region |
Gender (male/
female) |
Mean/ median age-yr. |
Study design | Population |
RA cohort/
PD cases |
Non-RA cohort/
comparators |
Period | Identification of RA | Identification of PD |
Matching/
adjustment confounder |
Mean/ median follow-up, yr. |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sung et al. (19) | Taiwan, China | 37,195/128,910 | RA cohort: 53.9, non-RA cohort: 53.4 | Cohort study | Taiwan NHIRD | 33,221 | 132,884 | 1998-2011 | ICD | ICD | Matched for age, sex, and year of RA diagnosis; adjusted for age, sex, NSAID use, and comorbidities (diabetes, hypertension, hyperlipidemia, coronary artery disease, head injury, depression, stroke). | RA cohort: 6.61, non-RA cohort: 6.70 |
| Rugbjerg et al. (20) | Denmark | 44,524/37,616 | PD: 73.0; non-PD: 65-75 | Case-control study | Danish National Hospital Register | 13,695 | 68,445 | 1986-2006 | ICD | ICD | Adjusted for chronic obstructive pulmonary disease | NP |
| Bacelis et al. (26) | Sweden | NP | PD cohort: median > 70; non-PD cohort: NP | Nested case-control study | Socialstyrelsen (the Swedish governmental agency managing medical registries) | 4,738 | 47,269 | 1997-2016 | ICD | ICD | Matched for birth year, sex, birth location, and time of follow-up | 1-20 |
| Li et al. (21) | Sweden | NP | NP | Cohort study | MigMed database (the center for primary health care research at the Lund University) | 52,994 | Standardized incidence ratios (Expected incidence rate) | 1964-2007 | ICD | ICD | Adjusted for age, period, socioeconomic status, region of residence, hospitalization of chronic obstructive pulmonary disease, and alcoholism and alcohol-related liver disease. | 1-44 |
| Li et al. (25) | European | NA | NP | Mendelian randomization study | Rheumatoid arthritis of European ancestry | Case (RA): 19,377; Case (PD): 33,647 | Control (non-RA): 53,911; Control (non-PD): 449,056 | NA | NA | NA | Removed single nucleotide polymorphisms searched in the GWAS Catalog that were reported to be associated with smoking and body mass index | NA |
RA, rheumatoid arthritis; PD, Parkinson's disease; NHIRD, National Health Insurance Research Database; NSAID, nonsteroidal anti-inflammatory drugs; ICD, International Classification of Diseases; GWAS, genome-wide association study; NA, not applicable; NP, not reported.