Association between comorbidities and disease activity in axial spondyloarthritis: results from the BSRBR-AS

Abstract

Objective: Whether comorbidities influence disease activity assessment in axial SpA (axSpA) is unclear. Comorbidities inflate DAS28 in rheumatoid arthritis through the patient global score. We examined whether axSpA disease activity measures are differentially affected, and whether comorbidities inflate the AS disease activity score (ASDAS) through the patient global component.

Methods: We used baseline data from the British Society for Rheumatology Biologics Register for AS, including 14 physician diagnosed comorbidities. Linear models were used to compare disease activity (BASDAI, spinal pain, ASDAS) and ESR/CRP according to comorbidity count, adjusted for age, gender, BMI, smoking, socioeconomic status, and education. The same models were used to examine whether the patient global score was associated with comorbidities, additionally adjusting for other ASDAS components.

Results: The number of participants eligible for analysis was 2043 (67% male, mean age 49 years); 44% had at least one comorbidity. Each additional comorbidity was associated with higher BASDAI by 0.40 units (95% CI: 0.27, 0.52) and spinal pain by 0.53 (95% CI: 0.37, 0.68). Effect size for ASDAS (0.09 units; 95% CI: 0.03, 0.15) was not clinically significant. ESR and CRP were not associated with comorbidity count. Depression, heart failure and peptic ulcer were consistently associated with higher disease activity measures, but not CRP/ESR. Patient global was associated with comorbidity count, but not independently of other ASDAS components (P = 0.75).

Conclusion: Comorbidities were associated with higher patient reported disease activity in axSpA. Clinicians should be mindful of the potential impact of comorbidities on patient reported outcome measures and consider additionally collecting ASDAS when comorbidities are present.

Keywords: AS; axial spondylarthritis; comorbidity; disease activity; patient global.

Fig. 1

Association between comorbidity count and disease activity Results shown as adjusted model coefficients with 95% CIs using participants with no comorbidities as the reference group; covariates were age, gender, BMI, smoking status, socioeconomic status and education. For example, participants with ≥3 comorbidities had 1.5 units higher BASDAI and 0.38 units higher ASDAS than those without comorbidities. ASDAS: AS disease activity score.

Fig. 2

Association between each comorbid condition and disease activity Results shown as adjusted model coefficients with 95% CIs compared with participants without each condition; covariates were age, gender, BMI, smoking status, socioeconomic status and education. For example, participants with heart failure (HF) had 1.7 units higher BASDAI and 0.59 units higher ASDAS than those without HF. ASDAS: AS disease activity score; COPD: chronic obstructive pulmonary disease; DM: diabetes mellitus; HF: heart failure; HTN: hypertension; IHD: ischaemic heart disease; PUD: peptic ulcer disease; TB: tuberculosis.

Fig. 3

Association between comorbidity count and other measures of disease severity Results shown as adjusted model coefficients with 95% CIs using participants with no comorbidities as the reference group; covariates were age, gender, BMI, smoking status, socioeconomic status and education. For example, participants with ≥3 comorbidities had 2.0 units higher BASFI and 0.79 units higher BASMI than those without. ASQoL: AS quality of life questionnaire; BASFI: Bath AS functional index; BASMI: metrology index.

Fig. 4

Association between each comorbid condition and other measures of disease severity Results shown as adjusted model coefficients with 95% CIs compared with participants without each condition; covariates were age, gender, BMI, smoking status, socioeconomic status and education. ASDAS: AS disease activity score; ASQoL, AS quality of life questionnaire; BASFI: Bath AS functional index; BASMI: metrology index; COPD: chronic obstructive pulmonary disease; DM: diabetes mellitus; HF: heart failure; HTN: hypertension; IHD: ischaemic heart disease; PUD: peptic ulcer disease; TB: tuberculosis.

Fig. 5

Association between the patient global score and comorbidity Results shown as model coefficients with 95% CIs; covariates were age, gender, BMI, smoking status, socioeconomic status and education. ASDAS, AS disease activity score; COPD, chronic obstructive pulmonary disease; DM, diabetes mellitus; HF, heart failure; HTN, hypertension; IHD, ischaemic heart disease; PG: patient global score; PUD, peptic ulcer disease; TB: tuberculosis.