6 year old with Duchenne's Muscular Dystrophy with extremely low BMD and BMC calculations secondary to local edema from acute vertebral fracture

Case Description

6 year old with Duchenne's Muscular Dystrophy (DMD), on chronic daily glucocorticoids, presented for his scheduled DXA screening, as per 2018 DMD Care Considerations Guidelines. He fell on his bottom the night before his appointment resulting in acute severe midline low back pain. GE Lunar iDXA densitometer was unable to automatically detect bone edges requiring manual ROI placement to complete the study. The Lumbar Spine L1-L4 BMD Z-score was - 7.5, with very low BMC of 0.93 grams. On Whole Body scan the Total Body Less Head (TBLH) Z-score= -2.0. No prior x- ray or DXA imaging available. Spine X-rays had subtle changes concerning for possible early vertebral compression. His pain remained moderate to severe over following 8 days, and had slow improvement with supportive care over subsequent weeks. Vertebral fracture was confirmed on repeat spine x-ray eight weeks after original study when noted to have 25% ht loss of L5, as well as compressive changes to L2, L3. Repeat DXA at this time showed L1-L4 BMD Z-score = -2.2 with BMC= 8.67g and TBLH Z-score remained -2.0. Acute injury, with its associated inflammation, edema, and possibly local hemorrhage, led to difficulties in edge detection and discrimination of bone versus soft tissue. This is not commonly reported in the manufacture or scientific literature as a source of error. Provider knowledge of this potential source of internal artifact should lead to either delay of imaging, or to repeat the study at an appropriate time if findings are inconsistent with expected outcomes in the setting of acute injury.

Credit

Michelle Clausen, Lead Nuclear Medicine/PET Technologist Children's Wisconsin