A 7-year-old boy has been listless and tired for the past several days. He is taken to the family physician who notes vital signs with T 36.6 C, P 100, R 16, BP 90/60 mm Hg. On auscultation of the chest there is a murmur of mitral regurgitation, an S3 gallop, and a friction rub. There is marked tenderness and swelling of the small joints of the hands as well as the ankles and wrists. There is a macular eruption with rounded borders concentrated on the trunk.

Laboratory findings include:

• Hemoglobin 14.1 g/dL

• Hematocrit 42.9%

• MCV 93 fL

• Platelet count 299,000/microliter

• WBC count 5,100/microliter

• WBC differential: Segs 53, bands 3, lymphs 32, 14 monos

• C-reactive protein elevated

• Troponin I slightly elevated

Question 7.1 - What cardiac manifestations are present?

There is an endocarditis with verrucous vegetations. There is evidence for myocarditis with tachycardia and dilation to produce valvular regurgitation. The friction rub suggests fibrinous pericarditis.

Question 7.2 - What additional laboratory test(s) would you order?

ASO, anti-DNAase, anti-hyaluronidase

Question 7.3 - What antecedent illness was he likely to have?

Strep throat with group A beta hemolytic streptococcal infection

Question 7.4 - Explain the pathogenesis for this disease.

This is an immunologic reaction from cross reactivity of antibodies to streptococcal M proteins to tissues such as those in the heart.