Dermatomiositis juvenil

Correct development of bone mass is essential during childhood. There are situations (such as certain diseases, taking certain types of drugs, prolonged rest...) that predispose to the loss of bone mass during childhood, giving rise to a disorder called osteoporosis (or its previous state, osteopenia). Preventing the onset of osteoporosis is crucial to allow correct development towards adulthood.

For this purpose, there is a test called bone densitometry, which measures bone mineral density, which can be performed with X-rays, ultrasound or radioactive isotopes; the most commonly used method is called DEXA (dual energy X-ray absorptiometry) and is performed in a densitometer, which measures the images and gives a figure of the amount of bone mineral per surface area. It is the most commonly used technique in paediatrics.

The values for diagnosing osteoporosis or "low bone density for chronological age" are not the same in adults as in paediatric patients. As a measure we do not use the adult t-score, but the Z-score (a score that compares the patient's bone density with children with normal bone density within the same age group). In people under 20 years of age, "low bone density for chronological age" is considered when the Z-score is less than -2 standard deviations (a type of statistical measurement that will not be explained here because of its complexity).

JDM, as well as some of the drugs necessary for its treatment such as corticosteroids, are known causes of osteoporosis in children and adolescents. For this reason, bone densitometry is recommended at diagnosis and every 12 months thereafter.