OSTEOPOROSIS IN ANOREXIA-NERVOSA

Bone loss in subjects with anorexia nevrosa was first demonstrated in 1984 and later confirmed by computed tomography and absorptiometry. Both cortical and trabecular bone is involved. Bone mineral content decreases early and has been estimated at 6 to 8% in 90% of the subjects with anorexia nevrosa. It is correlated with age and the duration of the anorexia and the associated amenorrhoea. Other factors including low weight, early onset, primary amenorrhoea, low serum oestradiol and high serum cortisol are also observed. In severe cases, fractures, similar to those observed in post-menopause osteoporosis, include vertebral wedge fractures, fractures of the ribs, the femoral neck, the forearm and the pelvis. In subjects with long-standing anorexia nevrosa, fractures often occur without weight loss and the diagnosis may be missed. A careful work-up is needed in all cases of bone loss in young women. The osteoporotic process is reversible in most cases if the anorexia can be overcome. Bone mineral content in cured subjects has been shorn to be the same as in age matched controls, but in severe long term cases, relapse and chronicity lead to continued bone loss. Normal menarche can generally be established with oestrogen therapy although significant gains in bone mineral content does not always follow. When progesterone-oestrogen therapy is combined with small dose fluorine (11.5 mg/day) bone mineral content has been shown to improve. Many subjects however refuse medication, especially oral contraceptives, hindering psychiatric care, which should always have first priority. The mechanism of bone loss in anorexia nevrosa is similar to that in post-menopause osteoporosis but may be favoured by other factors including alcohol intake and drug abuse. Certain authors have also hypothesized a common mechanism relating the amenorrhoea observed in women training for high performance sports and that in anorexia nevrosa. In clinical practice, first intention treatment should rely on hormone replacement but medication is often refused and can interfere with necessary psychiatric treatment. Sports appear to have a beneficial effect on femoral neck mineralization but in hyperactive subjects the effect is often inversed with increased bone loss. Patent osteoporosis can be treated with fluorine and biphosphonate.