Diagnosis of Low Bone Mass and Osteoporosis in Athletes

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DXA has been used as a diagnostic tool for the evaluation of bone health and particularly low BMD. BMD is normally distributed and is often expressed in standard deviation (SD) units relative to its T or Z distribution. The T distribution has a mean of zero, which corresponds to the mean of young healthy women. T-scores are used for the diagnosis of osteoporosis and osteopenia and to predict fracture risk in postmenopausal women [59]. Specifically, the World Health Organization has established cutoff scores for the diagnosis of osteoporosis and osteopenia for postmenopausal women [59]. In postmenopausal women, fracture risk nearly doubles for every SD below the young adult mean [62]. One more recent debate has been related to the fact that the same diagnostic strategies used for postmenopausal women (the distribution of T-scores and the comparison with the young adult mean) have been applied to premenopausal women, adolescents, and children. This seems problematic for three reasons: (1) Fracture data are lacking in premenopausal women, (2) it can be assumed that fracture risk is low in young women, and (3) peak bone mass has not yet been attained in adolescents and children. The International Society for Clinical Densitometry (ISCD) currently is proposing that BMD comparisons in premenopausal women, adolescents, and children be made relative to chronologic age, using the Z distribution [61]. To avoid a disease label in premenopausal women and to account for a skeleton of a young woman around or younger than age 20 years that has not yet attained peak bone mass, the ISCD recommends using Z-scores. Z-scores are expressed relative to chronologic age and allow for a better comparison of BMD values in individuals younger than age 20 years. As women become older, however, Z and T distributions are similar. According to the ISCD 2005 Official Position [9], a young woman is no longer considered osteoporotic or osteopenic with a low Z-score or T-score. Instead, her BMD now is considered low for chronologic age or is below the expected rangefor age. Although the International Olympic Committee (IOC) (IOC Position Stand, 2005) is generally in agreement with the ISCD's approach, its diagnostic criteria seem more conservative when considering athletic women. This is probably due to the fact that athletes, in general, should have higher BMD than controls, as was previously discussed. For both organizations, the diagnosis of osteoporosis is still relevant, but should not be based on densitometric criteria alone and should integrate other factors, such as hypoestrogenism or eating disorders (see Table 4 for a summary) [9,61]. The aforementioned cutoff values are likely to change again, and an update of the Female Athlete Triad Position Stand through the ACSM is soon to be published as well.

In many instances and particularly in the athletic setting, DXA is not always available for the assessment and evaluation of an athlete's bone health. It is reasonable to assume, however, that an athlete's bone strength has suffered if she

Table 4

Current recom

mendations for the diagnosis of low bone mineral density and osteoporosis in

premenopausal and postmenopausal women and young athletes

International

International

World Health

Society of Clinical

Olympic

Organization

Densitometry

Committee

Targeted

Postmenopausal

Premenopausal

Young,

population

women

women

premenopausal

athletes

Terminology

Osteopenia

BMD below

BMD below

expected range

expected range

for age

for age

Proposed

T-score: —1 to — 2.5

>20 years of age:

>20 years of age:

cutoff score

Z-score*: <—2

Z-or T-score: < —1

should be of

concern

Terminology

Osteoporosis

Low BMD for

Osteoporosis in

chronologic age

athlete with

or below expected

amenorrhea

range for age

Proposed

T-score: <—2.5

<20 years of age:

>20 years of age:

cutoff score

Z-score*: <—2

Z-score*: —2.5

*Z-and T-score may be similar in young women

>20 years old.

Data from references [9,59,61].

presents with amenorrhea for longer than 6 months or has experienced frequent phases of oligomenorrhea and possibly a stress fracture [9].

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