Bone/Parathyroid Case 6

A 56-year-old man with prostate adenocarcinoma, who has undergone a prostatectomy, androgen deprivation therapy, and chemotherapy including prednisone presents for an initial DXA referral. A DXA scan (Fig. A) shows total lumbar BMD of 0.815 g/cm2 and a T-score of –2.5. Individual lumbar T-scores were: L1 = –3.3, L2 = 1.6, L3 = –4.2, and L4 = –3.6. An artifact overlays L2 and the adjacent soft tissue. The patient discloses he had computed tomography (CT) imaging earlier the same day with oral and intravenous (IV) iodine-based contrast. 

 

References:  

Sala A, Webber C, Halton J, et al. Effect of diagnostic radioisotopes and radiographic contrast media on measurements of lumbar spine bone mineral density and body composition by dual-energy x-ray absorptiometry. J Clin Densitom. 2006;9:91-96.  

The International Society for Clinical Densitometry. Official Positions – Adult. 2015 ISCD. Available at: www.iscd.org. Accessed March 1, 2019. 

Morgan SL, Lopez-Ben R, Nunnally N, et al. The effect of common artifacts lateral to the spine on bone mineral density in the lumbar spine. J Clin Densitom. 2008;11:243-249. 

Spiro A, Hoang TD, Shakir MKM. Artifacts Affecting Dual-energy X-ray Absorptiometry Measurements. AACE Clinical Case Rep. Aug 2019;5(4):e263-266.  

Question 1

What is the next best step for further evaluation of this patient? 

A. Initiate medical treatment for osteoporosis
B. Interpret the DXA scan as it is
C. Review and compare with the previous DXA
D. Advise patient to come back for a repeat DXA in 7-10 days
Incorrect!
Correct!
Correct Answer
D. Advise patient to come back for a repeat DXA in 7-10 days

The artifact is consistent with the presence of oral contrast in the colon.  CT imaging performed one hour before the DXA scan, showed oral contrast at the hepatic flexure. The repeat scan done 10 days later, no longer showed the artifact (Fig. B). Iodine-based contrast enhances radiodensity by limiting the ability of X-rays to pass through tissue. It has been previously demonstrated that DXA performed immediately after administration of IV and oral iodine-based contrast causes increased measurement of bone mineral content; however, DXA repeated 7 days later produces results that are not significantly changed from baseline. In our patient, the contrast increased the BMD at L2, to such an extent that it nearly altered the DXA diagnosis from osteoporosis to osteopenia (option D). 

It is important to recognize the artifact on the DXA scan in order to make an accurate diagnosis.  Inaccurate diagnosis of DXA will affect the medical treatment and monitoring. A correct diagnosis of DXA (excluding artifacts) must be made first before initiating medical treatment for osteoporosis (option A). 
 
Interpretation of the DXA as it is with the presence of artifacts will result in an inaccurate diagnosis and wrong medical treatment decisions (option B). 
 

When interpreting DXA scans, physicians need to review and compare the current DXA with previous DXAs for interval changes.  However, this is the first DXA for this patient; thus, it is not applicable (option C).