USMLE® Step 1 style questions USMLE
A 64-year-old man in moderate distress comes to the emergency department after fainting at the grocery store and hitting the right side of his head on the way down. The patient states that he has fainted another time earlier this month, has worsening shortness of breath at rest and on exertion, and constant fatigue. Physical examination shows right periorbital pupura, macroglossia, hepatomegaly, and bilateral peripheral edema. Plain film chest radiography is normal, electrocardiography (ECG) is normal, and echocardiography shows marked dilation of both atria. The results of a myocardial biopsy stained with Congo red under polarized light is shown below. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
When cardiomyopathy develops as a way to compensate for some other underlying disease, such as hypertension or valve diseases, it’s called secondary cardiomyopathy.
When it develops all by itself, it’s called primary cardiomyopathy.
Restrictive cardiomyopathy describes when the heart muscle is restricted, meaning that it becomes stiffer and less compliant. However, the muscles and size of the ventricles stay about the same size, or only get slightly enlarged.
Normally, when blood fills the ventricles, they’re compliant; this means that they stretch out and allow more blood to fill in. When blood fills restricted ventricles, however, they can’t expand as much as they’re supposed to. Because stiffer, less compliant ventricles prevent the ventricles from stretching, less blood fills into the ventricle, which means the heart starts to fail to pump out enough blood to the body. Thus, restrictive cardiomyopathy causes heart failure; since filling happens during diastole, we call this a type of diastolic heart failure.
Now, several mechanisms can lead to stiffer heart muscles and restrictive cardiomyopathies. One of mechanisms is amyloidosis. Amyloids are proteins that have been misfolded; once misfolded, they become insoluble, and can deposit in various tissues and organs, making these tissues less compliant.