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USMLE® Step 1 Question of the Day: Dyspnea on Exertion and Fatigue

Osmosis Team
Published on Jun 8, 2022. Updated on Jun 5, 2022.

This week, we are sharing another USMLE® Step 1-style practice question to test your knowledge of medical topics. Today's case focuses on a 68-year-old woman complaining of dyspnea on exertion, fatigue, and chest pain. Past medical history includes carcinoma of the breast. Can you figure this one out?

A 68-year-old woman comes to the clinic complaining of dyspnea on exertion, fatigue, and chest pain. She also states that she has to use 3 pillows at night when she sleeps. Past medical history includes carcinoma of the breast, for which she received surgery and adjuvant radiation therapy but no chemotherapy. Temperature is 37.2°C (98.9°F), pulse is 80/min, respirations are 20/min, and blood pressure is 100/68. Physical exam shows jugular venous distension and bilateral leg edema. Cardiac auscultation shows S3 and S4 heart sounds. Electrocardiogram (ECG) shows low amplitude signals. 

Osmosis ECG.

Which of the following is the most likely cause of this patient’s disease?

A. Global dilation of the heart chambers

B. Myocardial amyloid deposition

C. Myocardial fibrosis

D. Granulomatous disease

E.  Myocardial iron deposition

Scroll down to find the answer!


The correct answer to today's USMLE® Step 1 Question is...

C. Myocardial fibrosis

Before we get to the Main Explanation, let's look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

The incorrect answers to today's USMLE® Step 1 Question are...

A. Global dilation of the heart chambers

Incorrect: Global dilation of the heart chambers is associated with dilated cardiomyopathy. Dilated cardiomyopathy is associated with chemotherapy (doxorubicin), not radiation therapy. This patient has restrictive cardiomyopathy.

B. Myocardial amyloid deposition

Incorrect: Myocardial amyloid deposition is a cause of restrictive cardiomyopathy, but this patient’s history of breast cancer with radiation therapy suggests post-radiation myocardial fibrosis as the most likely cause.

D. Granulomatous disease

Incorrect: Granulomatous disease of the heart associated with sarcoidosis is a cause of restrictive cardiomyopathy, but this patient’s history of breast cancer with radiation therapy suggests post-radiation myocardial fibrosis as the most likely cause.

E. Myocardial iron deposition

Incorrect: Myocardial iron deposition associated with hereditary hemochromatosis is a cause of restrictive cardiomyopathy, but this patient’s history of breast cancer with radiation therapy suggests post-radiation myocardial fibrosis as the most likely cause.

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Main Explanation

This patient with dyspnea on exertion, orthopnea, chest pain, past medical history of breast cancer treated with radiation therapy, and low amplitude electrocardiogram most likely has restrictive cardiomyopathy due to post-radiation myocardial fibrosis. Radiation generates reactive oxygen species in the tissue; over time, this leads to inflammation and can cause myocardial fibrosis.

Restrictive cardiomyopathy, which is the least common type of cardiomyopathy, is characterized by rigid ventricles which are unable to stretch appropriately and fill with blood. Therefore, the patient will have diastolic dysfunction with normal systolic function.


Causes of restrictive cardiomyopathy include:

  • Genetic: Familial amyloid cardiomyopathy (genetic mutation transthyretin protein)
  • Infiltrative: Senile cardiac amyloidosis (transthyretin misfolding with age), iron (hemochromatosis), sarcoidosis
  • Other: Post-radiation myocardial fibrosis, scleroderma


Diagnosis of restrictive cardiomyopathy is achieved via electrocardiogram (ECG), which shows low amplitude signals and short QRS complexes.

Treatment of restrictive cardiomyopathy includes treatment of the underlying cause if possible, loop diuretics, beta blockers, calcium channel blockers, and angiotensin converting enzyme inhibitors. However, heart transplant is the only definitive treatment.

Major Takeaway

Restrictive cardiomyopathy, which is the least common cause of cardiomyopathy, is characterized by increased rigidity of the ventricles and diastolic dysfunction. Electrocardiogram shows low amplitude signals and short QRS complexes. Treatment varies based on cause and disease severity.

References

Taunk NK, Haffty BG, Kostis JB, Goyal S. Radiation-induced heart disease: pathologic abnormalities and putative mechanisms. Front Oncol. 2015 Feb 18;5:39. doi: 10.3389/fonc.2015.00039. PMID: 25741474; PMCID: PMC4332338.

Yusuf SW, Sami S, Daher IN. Radiation-induced heart disease: a clinical update. Cardiol Res Pract. 2011 Feb 27;2011:317659. doi: 10.4061/2011/317659. PMID: 21403872; PMCID: PMC3051159.

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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB.