PMC9869350_01
Histopathologic findings of myocardial tissue, and coronary angiographic and intravascular modality images. Right ventricular tissues were obtained by endomyocardial biopsy. (A) Hematoxylin-eosin staining. Eosinophilic amorphous substances suggesting amyloid were accumulated in the myocardial interstitium. (B) Direct fast scarlet (DFS) staining detected diffuse amyloid deposition in the myocardium. (C) Immunostaining against transthyretin. (D) Electron microscopy detected infiltration of amyloid fibrils surrounding cardiomyocytes (arrows). (E) Coronary angiography demonstrated severe stenosis in the proximal left anterior descending artery (arrows). (F) Intravascular ultrasound imaging of the coronary artery plaque. Mild calcification was observed (arrowheads). (G) Optical coherence tomography imaging showed a plaque composed mainly of fibrous tissue with a low signal-intensity region (arrowheads), suggesting fibro-fatty plaque. (H) Coronary artery plaque was resected using directional coronary atherectomy catheter (arrowheads) before stenting.
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Coronary angiography revealed a severely stenotic lesion in the proximal left anterior descending artery, with a resting full-cycle ratio (RFR, a nonhyperemic index assessing functional myocardial ischemia) of 0.83, suggesting significant myocardial ischemia (Fig. 1E). Intravascular ultrasound and optical coherence tomography demonstrated a homogenous fibrotic or fibrofatty-like plaque (Fig. 1, F and G).
Coronary histologic finding of the resected plaque tissue. (A) Hematoxylin-eosin staining of the resected plaque tissue. The plaque was composed of fibrous tissue without the typical finding of a large amount of cholesterol accumulation and foam cell formation. (B) Masson's trichrome staining of the plaque tissue. (C) Direct fast scarlet (DFS) staining of the coronary plaque tissue. (D) Polarized light microscopy of the DFS staining specimen detected apple-green birefringence indicating amyloid deposition in the coronary plaque. (E) Electron microscopic finding of the resected plaque tissue. Greyish amorphous fibrillar substances were observed. The fiber thicknesses are approximately 10 nm, compatible with amyloid fibrils.
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Masson's trichrome staining showed brilliant blue fibrosis and amorphous bluish-gray components suggestive of amyloid (Fig. 2B). Direct fast scarlet (DFS) staining failed to show clear red amyloid deposition under ordinary light microscopy (Fig. 2C); however, polarized light microscopy demonstrated apple-green birefringence, indicating amyloid infiltration in the coronary plaque (Fig. 2D). Furthermore, electron microscopy detected an accumulation of 10-nm-thick amyloid fibrils in the coronary artery plaque (Fig. 2E).