P3C400: Diagnostic Challenge: Overlapping Features of Acute Rheumatic Fever and Lyme Disease in a 7-year-old Male

Introduction: Acute rheumatic fever (ARF) and Lyme disease are distinct conditions that can present with similar features. ARF is a nonsuppurative complication of group A streptococcal (GAS) infection that can lead to inflammation of the heart, joints, and skin. Lyme disease is a tick-borne illness that can cause a variety of symptoms including erythema migrans, migratory arthritis, heart block, and neurologic manifestations. We present a case of a 7-year-old male with overlapping features of these diseases.

Case Description: A 7-year-old male presented to the Emergency Department at the Children’s Hospital of Philadelphia with three days of fatigue and worsening migratory joint pain. Two weeks prior, he developed congestion and a sore throat that had not improved with amoxicillin-clavulanate. On exam, he was afebrile, and a new systolic ejection murmur was identified. His labs were notable for elevated ESR and CRP. An EKG showed first-degree AV block, and an echocardiogram showed carditis with mitral valve inflammation and moderate mitral regurgitation. Both his ASO titer and Lyme IgM and IgG serologies were positive. The patient therefore met Jones criteria for ARF based on a positive ASO titer indicating possible prior GAS infection, one major criterion (carditis with mitral regurgitation), and two minor criteria (polyarthralgia and elevated ESR and CRP). The patient’s positive Lyme serologies also indicated possible Lyme infection, which could explain his first-degree AV block and joint pain. Therefore, the patient was treated for both ARF and Lyme disease. He completed a two-week course of doxycycline and is currently receiving monthly intramuscular penicillin. His joint pain and elevated inflammatory markers have resolved.

Discussion: This case illustrates the complexity of diagnosing patients who present with features that could be consistent with ARF and/or Lyme disease. In 2015, the Jones criteria were modified to prioritize diagnostic specificity in populations with a low prevalence of ARF, such as the United States. However, data is lacking on the sensitivity and specificity of these updated criteria. According to one study, a single positive ASO titer has a sensitivity and specificity of 70% and 90%, respectively, for preceding GAS infection in the context of possible ARF . However, interpretation of ASO titers is complicated by frequent false/sustained positivity. Regarding Lyme serology, a recent study estimated that the positive predictive value of IgG > 2.0 is approximately 94%. However, other studies report higher rates of false-positive Lyme serology, suggesting that the accuracy of this test could vary with the laboratory and patient population.

Conclusion: ARF and Lyme disease share several features and can be challenging to distinguish in pediatric patients. In some cases, treatment of both conditions may be necessary to prevent complications. This case highlights the need for further research into diagnostic criteria and laboratory markers to distinguish these diseases.