Bone mineral density and quantitative ultrasound in adults with cystic fibrosis.
OBJECTIVE
With increasing life span osteoporosis becomes a more recognized problem in patients with cystic fibrosis (CF). The aim of this cross-sectional study in 75 adult patients with CF (mean age 25.3 years) was to assess the prevalence of low bone mineral density (BMD) by dual-energy x-ray absorptiometry (DEXA) and, for the first time, by quantitative ultrasound (QUS), and to identify predicting factors.


METHODS
Bone status was assessed at the lumbar spine (L2-L4) and the femoral neck by DEXA, and at the calcaneus by QUS (stiffness index). These data were correlated with a variety of clinical and anthropomorphic variables. Biochemical markers of bone turnover such as osteocalcin, bone-specific alkaline phosphatase, crosslinks in urine, 25-hydroxy vitamin D (25-OH vitamin D), parathyroid hormone, calcium and free testosterone were determined by standard assays.


RESULTS
The mean BMD T score (+/-s.e.m.) was -1.4+/-0.17 at the lumbar spine, and -0.54+/-0.16 at the femoral neck. The mean T score of the calcaneal stiffness index was -0.83+/-0.19. Based on a lumbar spine T score <-2.5 by DEXA, 27% of the patients had osteoporosis. Multiple regression analysis showed that the forced expiratory volume in one second (FEV1) and the use of oral glucocorticoids were independent predictors of low lumbar spine BMD, whereas body mass index (BMI) and the use of oral glucocorticoids were independent predictors of low femoral neck BMD. The stiffness index correlated moderately with BMD (0.49-0.62, P<0.0001). QUS had a sensitivity and specificity of only 57% and 89% respectively for diagnosing 'osteoporosis' (based on a femoral neck T score <-2.5 by DEXA). Positive and negative predictive values were 36% and 95% respectively.


CONCLUSIONS
Low BMD is frequent in adults with CF and is most strongly correlated with disease severity (BMI, FEV1) and the use of glucocorticoids. Calcaneal QUS might help to screen out patients with a normal BMD, but sensitivity and specificity were not sufficiently high to replace DEXA in these patients.
Flohr
F
F
Department of Internal Medicine II, Division of Endocrinology, University Hospital of Freiburg, Freiburg, Germany.
Lutz
A
A
App
E M
EM
Matthys
H
H
Reincke
M
M
D015502:Absorptiometry, Photon; D000284:Administration, Oral; D000328:Adult; D015992:Body Mass Index; D015519:Bone Density; D002111:Calcaneus / Q000000981:diagnostic imaging / Q000378:metabolism; D003430:Cross-Sectional Studies; D003550:Cystic Fibrosis / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000378:metabolism; D005541:Forced Expiratory Volume; D005938:Glucocorticoids / Q000008:administration & dosage / Q000627:therapeutic use; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000378:metabolism; D008297:Male; D010024:Osteoporosis / Q000378:metabolism; D012720:Severity of Illness Index; D014463:Ultrasonography
D005938:Glucocorticoids