Scottish Medical Journal

Editorial/Comments

OSTEOPENIA HAS A DIFFERENTIAL DIAGNOSIS

SMJ 2001: 46(6); 163-164

  Over the last 12 years the number of new patients referred to the bone clinic in Dundee has increased apparently exponentially from 30 per year to about 400. While we still receive referrals for the investigation and treatment of hypercalcaemia, Paget’s disease of bone, hypoparathyroidism and childhood bone diseases, almost all of the rise reflects patients referred because of concern about the possibility of osteoporosis. This increase reflects growing recognition of the place of bone densitometry and the availability of potent anti-resorptive drugs. Some of the increase also reflects the greater public awareness of osteoporosis promoted by the National Osteoporosis Society as well as by the drug companies.

  We recently carried out an audit of all the new patients seen over the four years 1997‑2000. Of 1207 patients, 1134 were referred because of concern about osteoporosis. Of these, 141 patients were, as a result of review of the clinical history, densitometric findings and laboratory evaluation, regarded as having osteoporosis of sufficient severity to justify intervention. In the great majority of these (121 patients) one or more risk factors for osteoporosis were identifiable. (Table I)  These patients could not be regarded as having ‘idiopathic osteoporosis’ and many had more than one risk factor. The management of each clearly needs to take account of the remediable risk factors identified.

During the same period no less than 66 patients had a new diagnosis made other than just osteoporosis. (Table II) Our experience of  five newly diagnosed patients with coeliac disease is similar to that of others.1

Our finding of 30 patients with osteomalacia emphasises the importance of undertaking appropriate investigation including serum parathyroid hormone and serum 25-hydroxyvitamin D where indicated.2 Our 16 newly identified male patients with hypogonadism underline the importance of checking for this disorder.3

  Six new patients with hyperparathyroidism were identified from patients referred for densitometry; during the same period 20 other patients were identified in referrals for the evaluation of hypercalcaemia. This group did not include any patients with a new diagnosis of Cushing’s syndrome but one was seen during the four year period. She had been treated elsewhere for osteoporosis before the diagnosis of Cushing’s syndrome was made.

  The number of patients and the variety of significant diagnoses highlights one major danger in the uncritical use of open access densitometry. Failure to recognise these disorders may lead to the prescription of drugs for osteoporosis which, in the light of the underlying cause of the osteopenia, are entirely inappropriate. Examples include prescription of bisphosphonates for patients with osteomalacia and prescription of calcium supplements or cyclical etidronate for patients with hyperparathyroidism.

One danger of bone density measurement is that it may be seen as providing the only treatable end-point, to the neglect of other factors contributing to fracture risk.4,5,6 We would draw attention to one additional hazard of the increasing use of open access densitometry. Some services provide results solely in terms of t-scores (the number of standard deviations below the mean for young adults) as opposed to z-scores (the number of standard deviations below the mean for an age-matched population).

  For the purposes of selecting patients requiring treatment, there are arguments in favour of both z-scores and t-scores and in reality neither is satisfactory.7,8  However, for identifying patients for further investigation, t-scores are entirely inappropriate. Figure 1 (not on web) illustrates the t-score findings in our patients. If the widely used cut-off figure of a t-score lower than minus 2.5 is used, many patients with significant remediable bone disease would not have been identified. The use of t-scores in this context is likely to lead to the under investigation of younger patients and the over-investigation of older patients.

We conclude that:

•  Most patients with osteoporosis have identifiable

 and often remediable risk factors underlying their

 condition.

•  Many patients referred simply for densitometry

or osteoporosis evaluation prove, on fuller investigation,

 to have significant diseases other than osteoporosis

 contributing to fracture risk.

•  T-scores are inappropriate for identifying patients

requiring further investigation.

C R Paterson, P A Mole, S J Wilson

Department of Medicine

Ninewells Hospital & Medical School

Dundee

References

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