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Cystic Fibrosis Centre of Tuscany Meyer Hospital Department of Pediatrics University of Florence Department of Internal Medicine Careggi Hospital Florence, Italy
Correspondence to: Filippo Festini, RN, BA, BSN, Department of Pediatrics, University of Florence, via L. Giordano 13, Florence, Italy 50132; e-mail: filippo.festini{at}unifi.it
To the Editor:
We read with interest the article by Stephenson and colleagues1 regarding the prevalence of vertebral fractures in adults with cystic fibrosis and their relationship to bone mineral density (BMD), and we would like to add some comments based on our clinical experience. In our cystic fibrosis center, 62 of 81 adult patients (76.5%) have undergone dual energy radiograph absorptiometry (DXA) at least once in the last 5 years; 25 of these patients are female and 37 are male (mean age, 27.1 years; SD, 3.2 years). At the time of DXA, none of the patients had been treated with drugs for osteoporosis before measuring bone density and none of them had received a lung transplant. BMD was measured using DXA (Delphi A S/N 70509; Hologic; Bedford, MA) in lumbar spine (L1-L4), and the results were expressed as an absolute value of BMD (grams per centimeter squared) and BMD T-score. Osteopenia was present in 45.1% of the patients (n = 28), and osteoporosis was present in 11.3% (n = 7) [World Health Organization diagnosing criteria2]. In all examined patients, vertebral fractures were excluded by clinical history and by lateral chest radiographic imaging performed in occasion of follow-up visits.
In accordance with the findings of Stephenson and colleagues,1 in our patients BMD values correlated with body mass index (BMI) values (R = 0.34, p = 0.006) and with FEV1 expressed as percentage of the predicted value according to age and sex (R = 0.21, p < 0.05), but also with Chrispin-Norman radiographic score (R = –0.27, p = 0.03). Similarly, a correlation was found between the BMD T-score values and the BMI values (R = 0.27 p = 0.03) and Chrispin-Norman score (R = –0.32, p = 0.02).
The mean value of BMI was significantly different between subjects with normal BMD (22.2 kg/m2; SD, 2.1 kg/m2) and those with alterations in BMD (20.3 kg/m2; SD, 2.5 kg/m2; t test, p = 0.002). A statistically significant difference was also found in the mean value of FEV1 between those patients with normal BMD (70.6%; SD, 23.8%) and those with alterations in BMD (55.2%; SD, 25.6%; t test, p = 0.02).
Our data are consistent with the findings of Stephenson and colleagues,1 even though in our population we did not observe any case of fracture. However, knowing that patients with fractures have a higher mean BMD value is likely not to have clinical relevance; it would have been interesting to know the proportion of patients with osteopenia and osteoporosis in the fracture and no-fracture groups. This information would imply important consequences from a preventive point of view, as it would offer clinicians a tool to evaluate the risk of pathologic fractures in cystic fibrosis patients according to their mineral bone status. Also, the presence of symptomatic osteoporosis is a contraindication for lung transplantation,3 and the risk of chest fractures developing may exclude a patient from a possible vital therapeutic opportunity.
Footnotes
The authors have no conflicts of interest to disclose.
The author has reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
References
St. Michael’s Hospital Toronto, ON, Canada
Correspondence to: Anne Stephenson, MD, St. Michael’s Hospital, Respirology, 30 Bond St, 6th Floor, Bond Wing, Toronto, ON, Canada M5B 1W8; e-mail: stephensona{at}smh.toronto.on.ca
To the Editor:
We are grateful for the interest and comments by Neri et al1 on our article,2 and we appreciate the opportunity to respond. We agree with the authors that the finding of an association between fractures and higher bone mineral density (BMD) is not clinically useful. The importance of this finding is more to emphasize the point that the association between T scores and fracture risk is unclear in patients with cystic fibrosis (CF). It may be erroneous to assume that the data from postmenopausal women applies to those with CF. At our institution, the dual energy x-ray absorptiometry report states the fracture risk based on the T score, and that this may be misinterpreted, especially for caregivers who are unfamiliar with CF-related bone disease. Based on this report, bisphosphonates may be prescribed for CF patients with osteoporosis; however, the ability of these drugs to decrease fracture risk has not been studied. Bisphosphonates seem to increase BMD in CF patients,34 but whether this translates into fracture prevention is unclear. To initiate the long-term use of a drug in a population of young premenopausal patients, which potentially may have effects on fetal development, must be considered carefully.
Neri et al1 recognized the importance of developing a tool to evaluate the risk of fractures in CF patients, which, we agree, is much needed. Using World Health Organization criteria,5 36% of the subjects in our no-fracture group had osteopenia and 9% had osteoporosis. Within the fracture group, 25% had osteopenia and none had osteoporosis. However, it is unclear how knowing this breakdown helps clinicians assess fracture risk, given the paradoxical findings of our study. The more important question is whether or not a different modality for evaluating BMD in CF can identify those patients who are at high risk for fracture based on an abnormal test result. DEXA may not be the appropriate tool for this population. Hopefully, future studies will help to clarify these issues.
References
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