May 20, 2015—Denver, Colorado—Smokers with vertebral fractures are at increased risk of thoracic kyphosis. This outcome of a comparative study was reported at the International Conference of the American Thoracic Society from May 15 – 20.
Elizabeth Anne Regan, MD, PhD of National Jewish Health, Denver, Colorado, explained that severe chest deformity has been associated with reductions in pulmonary function, particularly in association with kyphosis or scoliosis curves greater than 90 degrees. The impact of less severe degrees of kyphosis as seen with multiple vertebral fractures is less clear.
Dr Regan and colleagues hypothesized that multiple vertebral fractures and/or kyphosis would be associated with reduced forced vital capacity (FVC), total lung capacity (TLC), or functional residual capacity (FRC).
“We undertook the study,” Dr Regan said, “as part of a larger effort to study bone density and fractures in smokers with and without chronic obstructive pulmonary disease. That study showed that both male and female smokers and patients with chronic obstructive pulmonary disease are at increased risk of both osteoporosis and vertebral fractures. An important consideration for the public is that even former smokers may be at increased risk of osteoporosis and fractures though current smokers are at greater risk.”
“The next question that concerned us,” Dr Regan continued, “was whether vertebral fractures were negatively impacting the lung function.”
The investigators scored vertebral fractures using standard criteria and measured kyphosis angle (KA) from the superior endplate T-1 to the inferior endplate of T-12 with Cobb angles on 3317 CT scans from the COPDGene study. Two readers read each scan. Scans that failed agreement were adjudicated by a third reader to a final score.
Each subject also completed pre- and post-bronchodilator spirometry and provided information on respiratory symptoms, exacerbations, and quality of life. The relationship of kyphosis to FVC, TLC, and FRC was examined, adjusting for key covariates.
Vertebral fractures were identified in 1055 (37%) smokers. Subjects with factures were older, more likely to be non-Hispanic white (NHW) male, and had worse lung disease by FEV1 but no significant difference in FVC. Subjects with fractures had significantly increased KA (35.9 ± 10.8 vs 41.2 ± 11.9, P < .0001). Stepwise increases in KA were seen with the number of vertebral fractures to up four fractures and 45 ± 14.2 degrees kyphosis.
Predictors of greater kyphosis included NHW males, lower body weight, increased FRC, former smoker, lower FEV1, and the number of fractures. Oral corticosteroids, age, total lung capacity, percent emphysema, bone mineral density, and pack years of smoking were not predictors of kyphosis. Surprisingly, more kyphosis was significantly associated with higher FVC after adjustment for age, gender, race, height, and FEV1, P = .02).
In patients with emphysema >5.7%, there was no association of kyphosis to FVC. FVC is estimated for spirometry in an upright position, which may differ from kyphosis measured supine in the CT scanner. CT-derived volumes for TLC and FRC were also tested, and no decrease in either volume with kyphosis was found.
Dr Regan concluded that smokers with vertebral fractures are at increased risk of thoracic kyphosis. Increased thoracic kyphosis was associated with slightly higher FVC in subjects without significant emphysema, possibly due to changes in thoracic geometry. A reduction in lung volumes associated with thoracic kyphosis was not demonstrated.
“Thus far,” Dr. Regan added, “our data suggest that fractures, while painful, do not appear to reduce lung volume (FVC), even when they cause greater curvature or kyphosis of the spine. This is good news for patients with chronic obstructive pulmonary disease and a bit surprising to our research team.”
Dr Regan continued, “Future directions for my research will be to look at genetic associations with bone loss associated with smoking and chronic obstructive pulmonary disease. We would like to understand the reasons why bone is affected by lung disease and which patients are most at risk.”
“Genetic associations could become an important part of personalized medicine, allowing individuals to understand their unique risk profiles for disease and how they can either prevent adverse outcomes or begin treatment early. We may begin clinical trials testing smokers for low bone density and then start treatment to correct the problem before fractures occur.”