Bone scintigraphy for cardiac diagnosis
A high affinity for cardiac transthyretin of common bone scintigraphy tracers such as bifosphonates (99 mTc-DPD (3,3-Difosfono-1,2-propan-dicarboxic-acid) and 99 mTc-HMDP (hydroxy-methylenediphosphonate)) has been known for decades. A role for bone scintigraphy in diagnostic algorithm of cardiac amyloidosis was established in the diagnostic workup after the publication by Gillmore et al. in 2016 demonstrating the high diagnostic yield for transthyretin cardiomyopathy (2).
Amyloid bone scintigraphy is performed after intravenous injection of approximately 700 MBq 99 mTc-DPD/HMDP. Three hours after injection, a 20-minute whole body scan is performed. In case of cardiac uptake, proceeding with a SPECT/CT of the heart is recommended in order to characterise the localisation and distribution. Uptake of radiotracers is scored as described by Perugini (3). A positive amyloidosis bone scintigraphy (Perugini grade > 1) has > 98 % positive predictive value and specificity for transthyretin cardiac amyloidosis, provided that light chain amyloidosis is ruled out (1). If there is any evidence of monoclonal components and/or a pathologic kappa/lambda ratio, independent of Perugini score, light chain amyloidosis should be suspected (1).
In collaboration with colleagues from several medical specialities we have published updated Norwegian guidelines for diagnosis and treatment of amyloidosis (4).
Amyloid bone scintigraphy is available in all Norway's health regions for investigation of suspected cardiac amyloidosis. The method has high diagnostic accuracy for cardiac transthyretin and reduces the need for myocardial biopsy. Incidental cardiac uptake on a bone scan performed on other indications, such as malignancy, should result in a referral to a cardiologist.