Incidentally detected cardiac amyloidosis on ^99mTc-MDP bone scintigraphy

Cardiac amyloidosis (CA) is an important cause of restrictive cardiomyopathy and heart failure with preserved ejection fraction (HFpEF). At present, 3 bone-seeking tracers, ^99mTc-diphosphono-1,2-propanodicarboxylic acid (^99mTc-DPD), ^99mTc-pyrophosphate (^99mTc-PYP), and ^99mTc-hydroxymethylene diphosphonate (^99mTc-HMDP), have been evaluated for detecting CA, but they are not widely available. In contrast, methylene diphosphate (MDP) is widely available. However, only sporadic case reports have shown that MDP can accumulate in patients with CA. We report an 86-year-old man with multiple medical problems, including hypertension, hyperlipidemia, HFpEF, and a history of treated prostate cancer, who was referred for a ^99mTc-MDP bone scan to rule out bone metastasis. The bone scan was negative for bone metastasis, but there was mild tracer accumulation in the heart, suggestive of CA. Subsequently, CA was diagnosed on ^99mTc-PYP imaging. MDP may play a role comparable to other bone-seeking tracers in the diagnosis of CA and may be used as a noninvasive adjunct in the diagnosis of CA. Future research should compare MDP with other bone-seeking tracers for the diagnosis of CA. In addition, mechanistic studies on tracer binding to amyloid fibrils may help understand the pathophysiology of CA and facilitate the development of better and more specific tracers for CA.