Erythema marginatum rheumaticum

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A 12-year-old boy presented with high grade intermittent fever for 15 days with polyarthralgia involving the large joints of his extremities for last 5 days. His parents also noticed appearance of a pinkish coloured non-pruritic rash on the back of the trunk about a week after the onset of fever which resolved spontaneously only to reappear on the extensor surface of his right leg in the morning of the day of presentation. On examination, the patient was febrile with an oral temperature of 102 °F. The large joints of his extremities were not swollen but were tender on palpation. The rash was non-tender and non-pruritic, having elevated and reddened edges with a flat and clear centre (Fig. 1). Rest of the systemic examination was normal except sinus tachycardia. Complete blood count was normal except for raised ESR (90 mm), C-reactive protein (53 mg/L) and Anti-streptolysin O titre (754 IU). EKG was done and it revealed sinus tachycardia only. Trans-thoracic echocardiography documented thickened mitral valve leaflets with mild mitral regurgitation. Throat culture grew Streptococcus pyogenes. The patient was diagnosed to have acute rheumatic fever (ARF) based on the revised Jones criteria, treated symptomatically and was advised prophylactic benzathine penicillin G for secondary prevention until adulthood. Fig. 1 Erythematous annular papule over right lower limb with central clearing and serpentines spreading edges. Erythema marginatum, a form of annular erythema, is very uncommon in children experiencing the first attack of ARF [1]. The typical lesions have central clearing and serpenginous spreading edges and often are unnoticed by the patient or parent because they are painless and non-pruritic. It becomes even more difficult to detect the rash in dark-skinned people, explaining its rare occurrence (less than 1%) in ARF patients in non-white populations [2], [3]. Fever triggers the development of this rash, which perhaps explains the evanescent nature of the rash. Physicians should be careful not to overlook this rare but useful clinical manifestation of ARF, particularly in patients with subclinical valvular involvement to avoid potential late cardiac complications.