The Telltale Signs of Acute Rheumatic Fever

Because joint pain and elevated blood markers for inflammation are common to septic arthritis (SA) and acute rheumatic fever (ARF), it's easy to mistake the latter for the former, particularly in most of the developed world where rheumatic fever is rare. The difference in management, of course, is crucial, which presents yet another exquisite diagnostic dilemma.

This is almost as true for physicians in New Zealand as for those in US, except for the presence of a few groups -- the New Zealand Maori and New Zealand-born Pacific Island. These people have amongst the highest incidence of ARF in the world, says Matthew Boyle MD, who has used that misfortune to others' advantage.

Studying records of all patients under age 16 admitted with either condition to two New Zealand hospitals (Starship Children's Hospital and Middlemore Hospital, both in Auckland) between 2005 and 2012 allowed Boyle and his team to isolate 3 factors distinctive to ARF at presentation.

Comparison of records from 114 children with ARF and 111 children diagnosed with acute SA revealed that the former were significantly older than the latter (age 10 vs age 5), and less likely to be febrile. The hallmarks of ARF:

• Age older than 8.5 years at presentation;

• Serum erythrocyte sedimentation rate (ESR) >64.5 mm/hr (mean 90.2 for ARF vs 53.2 for SA, p<0.001)

• Serum white cell count (WCC) <12.1 x 10⁹/L (mean 12.3 for ARF vs 14.5 for SA, p<0.001).

C-reactive protein (CRP) was also significantly higher in ARF (mean 92.0 mg/L vs 87.4 mf/L for SA), but less so (p=0.003).

The team also found that, contrary to general impression, monoarthritis was not rare in ARF, accounting for 30% of cases.

Boyle, who presented these results at the American Academy of Orthopaedic Surgeons meeting now under way in New Orleans, has not seen a case of ARF recently, because he works currently as a sports medicine orthopaedic fellow at Duke University Medical Center in North Carolina. But he said he expects to find a few after August, when he will join Boston Childrens Hospital as a fellow in pediatric orthopaedics.