Do medical conditions predispose to the development of chronic back pain? A longitudinal co-twin control study of middle-aged males with 11-year follow-up.

BACKGROUND

Poor general health predicts the transition to chronic back pain (CBP), but the role of specific medical conditions in the development of CBP is unclear. The study aim was to examine the association of medical conditions with the development of CBP ("incident CBP"), while controlling for familial factors, including genetics.

METHODS

This was a longitudinal co-twin control study conducted in a nationwide United States sample from the Vietnam Era Twin Registry. The study sample included 3045 males without back problems at baseline, including 662 complete twin pairs, who were followed for 11 years. Baseline surveys inquired about self-reported medical conditions (arthritis, diabetes, hypertension, and coronary artery disease [CAD]). A medical comorbidity score was calculated based on the presence and/or treatment of 8 medical conditions. Covariates included age, race, and education. At 11-year follow-up, participants reported ever having had CBP. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated when considering twins as individuals, and in matched-pair co-twin control analyses adjusting for familial/genetic factors.

RESULTS

Mean age at baseline was 51 years and 17% of participants developed CBP over the 11-year follow-up. Arthritis was significantly associated with incident CBP in individual-level analysis (OR 1.8 [95% CI 1.4-2.2]), but not within-pair analysis (OR 0.9 [95% CI 0.4-1.9]. CAD (OR 1.6 [95% CI 1.0-2.3]), hypertension (OR 1.3 [95% CI 1.0-1.5]), and the medical comorbidity score (OR 1.2 [95%CI 1.1-2.2]) were significantly associated with incident CBP in individual-level analyses; associations in within-pair analyses were of comparable magnitude, but not statistically significant. Diabetes was not associated with incident CBP.

CONCLUSIONS

Arthritis, hypertension, CAD, and medical comorbidity score were associated with incident CBP in the current study. However, the association between arthritis and incident CBP was confounded by familial factors. This suggests that prevention or treatment of arthritis is unlikely to be useful for CBP prevention. Our findings cannot exclude the possibility of causal associations between CAD, hypertension, and medical comorbidities and incident CBP.