Tc-99 m Pyrophosphate Uptake in Atrial Amyloidosis With Hemorrhagic Mass　― A Diagnostic Pitfall Mimicking ATTR-CM ―

We previously reported a case of isolated atrial natriuretic peptide (ANP)-type atrial amyloidosis, presenting as a left atrial (LA) mass that resolved after presumed intramural hematoma rupture.¹ Here, we describe the long-term clinical course, focusing on technetium-99 m [^{99 m}Tc]-pyrophosphate (PYP) uptake dynamics.

A 40-year-old hypertensive woman with no prior cardiac history presented with acute chest pain, dyspnea, and a large LA mass. Chest X-ray revealed pulmonary congestion and cardiomegaly. Laboratory tests showed elevated white blood cell count of 16,600/μL, C-reactive protein (18.6 mg/dL), and B-type natriuretic peptide (118 pg/mL). Echocardiography demonstrated normal left ventricular (LV) wall motion and a giant multivesicular LA mass (58×39 mm) adherent to the thickened posterior LA wall causing functional mitral stenosis with a 4-mmHg LA–LV gradient (Figure A). Coronary angiography was normal. Cardiac magnetic resonance imaging showed LA wall thickening and a mass with high T2 signal. While treating her heart failure with medications including diuretics and preparing for surgery, the mass rapidly regressed on day 11, leaving only partial wall thickening. Her symptoms improved, and she was discharged on enalapril, spironolactone, and bisoprolol.

Figure.

Left atrial (LA) mass on admission echocardiogram (A, arrows), [^{99 m}Tc]-PYP planar scintigraphy (B), and SPECT (C,D). Follow-up echocardiographic (E), [^{99 m}Tc]-PYP planar (F), and SPECT images (G,H) at 1 year after LA appendectomy.

However, 1 year later, due to persistent LA wall thickening and new-onset atrial fibrillation requiring anticoagulation, she underwent thoracoscopic LA appendectomy. Histology and mass spectrometry confirmed isolated ANP-type atrial amyloidosis, with negative staining for transthyretin, immunoglobulin light chains, and amyloid A.¹ Although ^{99 m}Tc-PYP scintigraphy showed accumulation in the upper cardiac silhouette, uptake was confined to the LA (Figure B), SPECT images localized the uptake to the atrial wall (Figure C,D). On follow-up 1 year later, no mass was observed, and the abnormal uptake had resolved (Figure E–H). Recent guidelines support noninvasive diagnosis of transthyretin amyloid cardiomyopathy based on ^{99 m}Tc-PYP scintigraphy, but this case highlights a diagnostic pitfall, as false-positive uptake can occur due to inflammation from hematoma or iatrogenic procedural stimuli to the heart.

Funding

None.

Reference

• 1.   Makino M, Moriwaki K, Fujimoto N, Kirii Y, Mizutani H, Goto T, et al. Vanishing left atrial mass in a middle-aged woman: Spontaneous intramural left atrial hematoma in isolated atrial amyloidosis. Circ Cardiovasc Imaging 2024; 17: e016905.