Background Juvenile dermatomyositis (JDM) is an idiopathic inflammatory myopathy associated with chronic inflammation. The mainstay of management of JDM is corticosteroids which together with the associated chronic inflammation may render the patients at risk of poor bone mineralization. It is therefore important to determine the bone mineral density (BMD) status of JDM patients to inform appropriate decisions on therapeutic and preventive interventions. Only a few studies have reported on the bone mineral density status in JDM patients.
Objectives To determine the bone mineral density (BMD) of JDM patient seen at the Red Cross and Groote Schuur hospitals in Cape Town between 2004 and 2013.
Methods We carried out a retrospective folder review of JDM patients who satisfied the Bohan and Peter criteria for probable dermatomyositis. The demographic and clinical characteristics of the patients were documented. Lumbar spine BMD measurements (using dual Xray absorptiometry - DXA) and Z scores were also recorded. For this study, the following reference values for BMD Z-scores were used: normal more than or equal to –1.5 SD, low BMD score less than –1.5 SD.
Results Patient characteristics – Nine DXA scans were identified in eight patients; five female and three male. Their median age was 3.65 years at disease onset and 4.1 years at diagnosis. The median age at study (DXA) evaluation was 7.8 (range 3.9-15.9) years and the median duration of follow up prior to DXA was 2.1 (range 0.8-13.5) years.
Clinical characteristics – All patients were treated with corticosteroids and were on prednisolone at the time of the DEXA studies. The median duration of steroid use was 25 (range 6-151) months. Five of the 9 patients had calcinosis while none had documented compression fracture of the spine.
The median lumbar spine BMD was 0.48 (range 0.29 - 1.08) g/cm2 with median Z- score of -0.5 (range -4.4, 1) SD. Three patients had low BMD with Z-scores lower than -1.5 SD (-1.8, -3.4 and -4.4). The spine BMD Z-scores correlated positively with age adjusted BMI Z-scores (R=0.86, p=0.01) and negatively with age at disease onset (R=-0.86, p=0.01). However, there was no significant correlation between the spine BMD and duration of untreated disease (R=0.63, p=0.12), duration of steroid use (R=0.36, p>0.1) as well as with average steroid dose (r=-0.32, p>0.1). Further, there was no statistically significant difference in BMI scores, age at onset, duration of untreated disease and steroid dose between the patients with low BMD and those with BMD within reference level.
Conclusions Our study shows that osteopenia and osteoporosis may occur in upto 3 in 9 (33%) of JDM patients. Further studies may be needed to inform formulation of guidelines on the utility of serial BMD measurements and therapeutic interventions in the prevention and management of osteopenia and osteoporosis associated with JDM.
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Acknowledgements Department of nuclear medicine, Groote Schuur Hospital, Cape Town for the DXA reports.
Disclosure of Interest None declared