The association between RA and depression has been well documented but so far there is not much research at a national level and none using a quick classification system of RA. The purpose of this study is to further determine if this association varies by differing severity in functional status of RA patients.
This study involved a retrospective pooled cross-sectional analysis of the Household Component of Medical Expenditure Panel Survey (MEPS) for the years 2004-2006. Each year's medical conditions file was merged with the person-level consolidated file. A total of 289 individuals comprised the final adult sample of RA and related diseases. RA cases were classified into four classes of functional status according to the ACR classification criteria. Tendency towards depression was ascertained by Patient Health Questionnaire (PHQ-2) scores with scores greater than or equal to three classified as high tendency towards depression. Multivariate logistic regression with survey weights was done using SAS 9.1.
After controlling for other relevant factors, patients belonging to Class III RA were 5.92 times more likely and those belonging to Class II RA were 3.78 times more likely to have high tendency towards depression as compared to Class I RA patients. Older age groups (>or=68 years) and physical activity were other significant predictors but in a negative direction, whereas a co-morbidity index of two showed a significant positive association.
The study provides important evidence that in a nationally representative sample of US non-institutionalized civilians, there is a strong association of depression to RA and related diseases by functional severity. However, the findings should be interpreted with caution because the data does not offer any information on duration in relation to PHQ-2 scores, thus making it hard to deduce if tendency towards depression was present before the diagnosis of RA. Furthermore, disease-specific and data-specific validation of the Charlson comorbidity index has not been done which leaves the possibility of residual confounding.