USMLE Step 3 - Question 23

A 35 year old male with no past medical history presents with increasing shortness of breath and dyspnea on exertion and lower extremity edema increasing over the past month. His temperature is 37.0, blood pressure 90/60, heart rate 100, respirations 20, and oxygen saturation 95% on room air. Physical examination reveals decreased breath sounds at the left base without wheezing, elevated jugular venous pressure markedly worse with inspiration, a regular rhythm with an S4 heart sound and 2+ lower extremity pitting edema. Laboratory studies are normal. Cardiac biopsy revealed green birefringence with Congo red staining. Genetic testing reveals a mutation in the transthyretin gene. Which of the following is the correct diagnosis?

A. Constrictive pericarditis

B. Restrictive cardiomyopathy

C. Dilated cardiomyopathy

D. Hypertrophic obstructive cardiomyopathy

This patient has restrictive cardiomyopathy from amyloidosis. The primary problem with restrictive cardiomyopathy is the infiltration/deposition of proteins into the myocardium itself making it difficult for the myocardium to relax. The cardiac form of amyloidosis specifically results from a mutation in the transthyretin protein gene making is susceptible to myocardial deposition. Restrictive cardiomyopathy can occur from other causes as well including hemachromatosis and sarcoidosis. The symptoms are those of congestive heart failure (dyspnea on exertion, lower extremity edema, and generalized fatigue). Physical exam findings include a Kussmal's sign (markedly increased jugular venous pressure with inspiration, which is the opposite as in a normal person), a blunted Y descent in the jugular venous waveforms, and at times distant heart sounds. ECG findings are non-specific but may show low voltage due to dampened elecrical activity from the protein-laden myocardium. The only real treatment is heart transplant, but with hemachromotosis treating the iron overload can improve and sometimes reverse the cardiac symptoms.