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Hormones and proximal myopathy
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By now readers of my blogs must know that I receive a large number of e-mails containing abstracts of recent articles. When I can I try and access the full text because an abstract is infrequently enough to fully appreciate the work that is being reported. The article I am commenting on today* is one that I have not yet read in full but the point I want to get across doesn’t depend too much on that.
The abstract reported that in elderly persons with diabetes the risk of falling increased with higher parathyroid hormone levels. The data was that “serum parathyroid hormone was 53.5±30.0 pg/mL in non-fallers and 62.6±46.2 pg/mL in fallers (P=.01).” The information is important and probably reflects the known adverse effect of parathyroid hormone on proximal muscle function. Whether this is a direct effect of parathyroid hormone or is mediated via a lower 25-hydoxyvitamin D level, which leads to a rise in parathyroid hormone, is unclear.
An association between a number of hormones (thyroxine, glucocorticosteroids, parathyroid hormone and active metabolites of vitamin D) and proximal myopathy has long been known. I am uncertain of the mechanism(s) and unaware if there is a common link between these associations.
When the myopathy is severe you may well recognize or at least suspect it as the patient comes into the exam room. That is uncommon. One way to check while the patient is in the exam room is to see if they can stand from a sitting position with their arms folded. There are a number of reasons why a patient might not be able to complete this task, not just an endocrinopathy. Irrespective of the cause this is an important clinical observation that requires attention. Not just determining the etiology, but offering advice about safety and fall prevention.
The other point I want to make briefly about the article I have cited is the laboratory data. In group studies the difference between a parathyroid hormone level of 53.5 and 62.6 is statistically significant and gives a clue to disease processes. However, in the individual patient a change from 53 to 64 may simply reflect day-to-day fluctuations and variability in the assay method. A parathyroid hormone level of 53.5 or 62.6 is not 53.5±0 or 62.6±0. For lab data that you monitor regularly it is worthwhile checking with the lab about variability of the measurements.
*J Am Geriatr Soc. 2008;doi:10.1111/j.1532-5415.2008.01966.x