Soru

A male patient, aged $62$, is evaluated in the internal medicine clinic for a four-month history of progressive dyspnea on exertion, leg swelling, and spontaneous bruising. He also reports bilateral hand numbness that predominantly affects the thumb, index, and middle fingers. His only known medical history is essential hypertension. Blood pressure is $110/70$ mm Hg, heart rate is $88$/min, and respiratory rate is $16$/min. Jugular venous pressure is elevated at $10$ cm H $_2$ O. Pulmonary auscultation is clear. Cardiac examination reveals a regular rhythm with an S4 gallop and no murmurs. Dermatologic examination shows periorbital ecchymoses and pinch purpura on the upper chest. Bilateral $2+$ pitting edema is present up to the knees.

Laboratory studies reveal:
Hemoglobin: $10.2$ g/dL
Platelet count: $165,000$/mm $^3$
Creatinine: $1.8$ mg/dL
Calcium: $10.8$ mg/dL
Prothrombin time: $13$ seconds
Activated partial thromboplastin time: $30$ seconds
Urinalysis: $3+$ protein

Electrocardiogram demonstrates normal sinus rhythm with low voltage QRS complexes in the limb leads. Echocardiogram demonstrates severe concentric left and right ventricular thickening with a left ventricular ejection fraction of $55\%$ and a diffuse, granular sparkling appearance of the myocardium.

Which of the following is the most likely diagnosis?