A child is admitted to the hospital with suspected rheumatic fever. Which of the following observations is not confirming the diagnosis?
A. A reddened rash visible over the trunk and extremities.
B. A history of sore throat that was self-limited in the past month.
C. A negative antistreptolysin O titer.
D. An unexplained fever.
Correct Answer: C. A negative antistreptolysin O titer.
Rheumatic fever is caused by an untreated group A B hemolytic Streptococcus infection in the previous 2-6 weeks, confirmed by a positive antistreptolysin O titer. ASO is a test used to detect streptococcal antibodies directed against streptococcal lysin O. An elevated titer is proof of a previous streptococcal infection. It is usually more elevated after a pharyngeal than skin infection, while the ADB is typically elevated regardless of the site of the infection.
Option A: Rheumatic fever is characterized by a red rash over the trunk and extremities. The individual lesions of erythema marginatum are evanescent, moving over the skin in serpiginous patterns. Likened to smoke rings, they have a tendency to advance at the margins while clearing in the center.
Option B: Although estimates vary, only 35%-60% of patients with rheumatic fever recall having any upper respiratory symptoms, most commonly, sore throat, in the preceding several weeks. Studies in developed countries have established that rheumatic fever followed only pharyngeal infections and that not all serotypes of group A streptococci cause rheumatic fever.
Option D: Other symptoms of rheumatic fever include fever. The average duration of an untreated ARF attack is 3 months. Chronic rheumatic fever, generally defined as disease persisting for longer than 6 months, occurs in less than 5% of cases.