Estimation of prevalence of transthyretin (ATTR) cardiac amyloidosis in an Australian subpopulation using bone scans with echocardiography and clinical correlation

Background Bone scans differentiate transthyretin (ATTR) cardiac amyloidosis from light chain amyloidosis and other causes of increased left ventricular (LV) wall thickness. We examined the prevalence and implications of cardiac uptake in the general population. Methods Patients were included based on having undertaken a bone scan for non-cardiac indications using Technetium 99m hydroxymethylene diphosphonate (HMDP) or Technetium 99m methylene diphosphonate (MDP). Blinded image review was undertaken. Positive was defined as cardiac uptake >= rib AND heart/whole body ratio (H/WB) > 0.0388. Echocardiography and clinical records were reviewed. Results 6918 patients were included. 15/3472 HMDP scans were positive (14 males, 1 female): none in individuals aged < 65; 1.44% in males and 0.17% in females >= 65; 6.15% in males and 1.69% in females >= 85. Only 1/3446 MDP scans were positive. All HMDP positive patients had increased septal wall thickness on echocardiography. H/WB correlated positively with LV mass, and negatively with LV ejection fraction. No individual had an explanation other than ATTR for their positive scan. Conclusion In this Australian subpopulation, the prevalence of positive bone scans consistent with cardiac ATTR is 0% in individuals aged < 65. Prevalence increased with age, reaching 6.15% in men >= 85. The amount of HMDP uptake correlated with echocardiographic features of more advanced cardiac involvement. MDP does not appear useful in ATTR.