An 8-year-old boy is brought to the office for rapid and irregular movements of his hands for one week. His parents say that he is also making unintentional "funny faces" and has trouble controlling the volume of his voice. His temperature is 38.9 C (102 F). On physical examination, the boy moves his hands frequently and erratically. He has a new III/VI systolic murmur and several circular, faintly erythematous lesions on his abdomen. Which of the following is the most likely mechanism for this patient's condition?

Question

An 8-year-old boy is brought to the office for rapid and irregular movements of his hands for one week.  His parents say that he is also making unintentional "funny faces" and has trouble controlling the volume of his voice.  His temperature is 38.9 C (102 F).  On physical examination, the boy moves his hands frequently and erratically.  He has a new III/VI systolic murmur and several circular, faintly erythematous lesions on his abdomen.  Which of the following is the most likely mechanism for this patient's condition?

Quizplus · Accepted Answer

11ec160b_3afe_5384_9249_914054b4e7be_MD0001_00 This patient has acute rheumatic fever, an immune-mediated disease following an untreated group A streptococcal (GAS) infection. Antibodies against GAS cross-react with host tissues due to molecular mimicry between GAS antigens and cardiac and central nervous system antigens. Specifically, antibodies directed against GAS antigens, M protein and N-acetyl-beta-D-glucosamine, subsequently attack myosin, a cardiac protein, and lysoganglioside, a neuronal cell surface protein. The major manifestations of acute rheumatic fever include arthritis, pancarditis, Sydenham chorea, erythema marginatum, and subcutaneous nodules. This patient's murmur is likely due to acute mitral regurgitation from pancarditis. Sydenham chorea presents with non-rhythmic movements of the hands, feet, and face. Patients often have sudden changes in voice pitch and volume. Erythema marginatum presents as faintly erythematous, circular lesions with central clearing that come and go on the trunk and extremities. (Choice A) Superantigens cause a tremendous release of cytokines through nonspecific T cell receptor activation, leading to acute fever, hypotension, and erythroderma. This is the mechanism of action of the toxic shock syndrome exotoxins produced by both Staphylococcus aureus and Streptococcus pyogenes. (Choice C) An embolic stroke from infective endocarditis can present with fever, a new-onset murmur, and focal neurologic deficits. In addition, Janeway lesions, Osler nodes, and Roth spots are specific findings of infectious endocarditis. The most common pathogens are S aureus, viridans group streptococci, and enterococci. (Choice D) The deposition of streptococcal antigen immune complexes in glomeruli causes post-streptococcal glomerulonephritis, a type III hypersensitivity reaction. Patients have microscopic or gross hematuria, edema, hypertension, and proteinuria. (Choice E) Scarlet fever is caused by the body's response to an erythrogenic (pyrogenic) toxin released by group A Streptococcus. It presents with a diffuse, erythematous, "sandpaper"-textured rash most notable in the skin folds (eg, inguinal, axillary, antecubital areas). Scarlet fever can occur with pharyngitis and can lead to acute rheumatic fever if untreated. Educational objective: Acute rheumatic fever is an autoimmune reaction following an untreated group A streptococcal pharyngitis. Anti-group A Streptococcus antibodies (eg, anti-M protein, anti-N-acetyl-beta-D-glucosamine) cross-react and attack cardiac and central nervous system antigens. __________ References: Rheumatic fever, autoimmunity, and molecular mimicry: the streptococcal connection. (http://www.ncbi.nlm.nih.gov/pubmed/24892819) Streptococcus and rheumatic fever. (http://www.ncbi.nlm.nih.gov/pubmed/22617826) Acute rheumatic fever and streptococci: the quintessential pathogenic trigger of autoimmunity. (http://www.ncbi.nlm.nih.gov/pubmed/24894108)

An 8-Year-Old Boy Is Brought to the Office for Rapid