Studies related to bone mass in patients with cystic fibrosis

Abstract

Cystic fibrosis is the most common genetic disease that causes respiratory failure and earlydeath. The lifespan of these patients has gradually increased due to improved generaltreatment, but concurrent with this, new complications have emerged, and changes in bonemineral density (BMD) have been stressed as a major problem. The aim of this work was tostudy BMD in normal growing patients with cystic fibrosis (CF) and relate to factors ofimportance for bone mass, like vitamin D, calcium and parathyroid hormone.Seventy consecutive patients, aged 6-49 years with CF were investigated with dual energy Xrayabsorptiometry (DXA) of the lumbar spine (LS) and the femoral neck (FN) and 54 ofthem were followed prospectively for two years. The results were related to clinical,anthropometric and biochemical data. The average z-score of BMD was decreased in the LSin 40% of children and adults. Osteoporosis was rare. BMD increased at a normal rate duringthe two years, and correlated to body weight and lung function. Intact parathyroid hormonewas positively correlated to the increase of BMD in both LS and FN during childhood. Therewere no correlations to serum levels of vitamin D and calcium but patients with pathologicalblood sedimentation rate and serum levels of immunoglobulin G had significantly lowerBMD than those with normal values.In fourteen young men with CF and 42 healthy controls the DXA investigations werecomplemented with peripheral quantitative computerized tomography (pQCT). No differencesin bone parameters between the two groups were obtained but CF patients, chronicallycolonized with Pseudomonas areuginosa, had significantly lower trabecular BMD than notcolonized patients.Low serum levels of vitamin D despite regular supplementation has frequently been reportedin CF. The fact that Sweden is located on a high latitude (Göteborg, N58), motivated us tostudy if these serum levels would improve during the dark season by regular ultraviolet B(UVB) radiation. An intervention study was performed for 6 months and a significant increasein the serum level of vitamin D was obtained in the UVB group. The osteocalcin levelsdecreased reflecting a decreased bone loss but the PTH values did not decrease after thetreatment as expected.Conclusions: Although patients with CF had normal anthropometry, still 40 % had decreasedBMD (z-score less than -1SD) in the cross sectional study. The influence of CF on BMD maystart early in life since the growth rate of BMD during 2 years was normal and did not differfrom that in healthy controls. The studies imply that low BMD in CF is multifactorial andassociated with infection and nutritional parameters. We suggest that our result of normalBMD compared to the general literature might be related to several factors in our treatmentprogram, including regular physical activity, short courses of high doses of antibiotics at verymild symptoms and a good nutritional support. UVB radiation would be a goodsupplementary treatment, but has practical difficulties on a routine basis .