Clinical and laboratory factors associated with bamboo spine in patients with axial spondyloarthritis: are there clues for bamboo spine?

Objectives: To analyse the clinical and laboratory factors associated with bamboo spine.
Methods: Data of patients fulfilling the 2009 ASAS classification criteria for axial spondyloarthritis, registered in the national, multicentre, longitudinal, and observational database of TReasure was analysed. Radiographs were assessed using the Bath Ankylosing Spondylitis Radiologic Index (BASRI). Data of patients with a bamboo spine (Group 1) was compared to data derived from patients with a longstanding disease of at least 15 years but no syndesmophytes (Group 2).
Results: Out of the 5060 patients, 1246 had eligible radiographs. There were 111 patients (8.9%) with a bamboo spine. Male sex was more common among patients with bamboo spine. The median BMI of 27.7 (25.8-31.1) in Group1 was higher than the BMI of 25.9 (22.9-29.2) in Group 2 (p<0.001). Hip arthritis, present or documented by a physician, was more common in Group 1 [(58/108 (53.7%) vs. 35/103 (34%), p=0.004]. There was a tendency towards a more prevalent enthesitis in these patients [29.1% (25/86) vs. 15.9%(11/69), p=0.054]. HLA-B27 status did not differ between groups. Smoking was more prevalent in Group 1. Multivariate logistic regression analysis revealed that male sex, body mass index, hip arthritis, and enthesitis are associated with bamboo spine in axSpA.
Conclusions: Bamboo spine was more common in the male sex and associated with a delay in diagnosis, high BMI, hip involvement, and enthesitis. The constellation of increased body weight, hip arthritis, and enthesitis may imply that mechanical stress contributes to radiographic damage in the presence of chronic inflammation.