A 38-year-old immigrant woman comes to the Emergency Department with right-sided weakness and slurring of her speech. Initial imaging and studies are obtained, and she is found to have suffered an ischemic stroke and is treated appropriately. When you go to examine her, she has an irregularly irregular pulse, and on cardiac examination she has an early diastolic high-pitched opening snap at the apex followed by a low-pitched diastolic rumbling murmur. Upon further discussion with the family, they indicate that she does not have any chronic medical problems and has not been to the doctor since she was a baby. She had frequent throat infections as a child, but these always resolved without treatment. She takes no medications and does not smoke or drink alcohol.
The mechanism by which this condition developed is most similar to which of the following other conditions?
A. Infective endocarditisGuillain–Barré syndrome. This is a difficult question that assumes a strong understanding of mitral stenosis, including the mechanism, diagnosis, and potential complications. This woman suffered a stroke, which is rare in her age group. A careful reading of the vignette shows that the patient had mitral stenosis and atrial fibrillation, both of which increase the propensity for a clot to form in the left atrium and embolize to the cerebral circulation to cause an ischemic stroke. The patient’s history, obtained from her family, raises the suspicion for rheumatic heart disease as the cause of the patient’s mitral stenosis. This is a common cause of mitral stenosis in developing countries and usually becomes symptomatic in the 30s. It is caused by Streptococcus pyogenes (Group A β-hemolytic strep). This is a reason why strep throat is important to diagnose and treat with antibiotics. Rheumatic heart disease is usually caused by repetitive strep infections, which was seen in this patient. The mechanism can be explained by the process of molecular mimicry, in which antibodies developed after exposure to an infectious agent cross-react with self antigens. One of these self antigens is present on the mitral valve, causing an autoimmune reaction which leads to scarring with subsequent repair and fibrosis, ultimately resulting in stenosis of the mitral valve. (E) Guillain–Barré syndrome is similarly a result of autoantibodies developed after exposure to an infectious agent (Campylobacter, Mycoplasma, viruses such as CMV and HIV, etc.) via the same mechanism of molecular mimicry. It results in an ascending paralysis due to demyelination of peripheral nerves.
peripheral nerves. (A) Infective endocarditis may affect the mitral valve, but damage of the valve commonly leads to a regurgitant murmur (rather than stenosis). The mechanism is by direct infection of the valve and not by an autoimmune process. (B) Cystic fibrosis is an autosomal recessive disease caused by a mutation in the CFTR gene encoding a chloride channel. (C) Graves disease is the result of autoantibodies against the TSH receptor, causing unregulated stimulation and secretion of thyroid hormone. There is no preceding infectious agent, and the autoantibodies are activating (not destructive). (D) Sarcoidosis is a granulomatous autoimmune disease but is not preceded by an infectious agent causing molecular mimicry.