SAN FRANCISCO — A child with fever of unexplained origin and an abscess in the right thigh ultimately was diagnosed with systemic juvenile idiopathic arthritis after tests showed the abscess was sterile, Sara Fitzpatrick said in a poster presentation at the annual meeting of the American Academy of Pediatrics.
The English medical literature contains no previous reports of systemic juvenile idiopathic arthritis (JIA) presenting with a sterile abscess, said Ms. Fitzpatrick, who worked on the report with Elizabeth C. Chalom, M.D., director of pediatric rheumatology, and other associates at St. Barnabas Medical Center, Livingston, N.J.
The most common cause of fever of unknown origin in childhood is infection, she noted, and the abscess and other findings initially misled clinicians into thinking that was the case with this child.
The 21-month-old boy entered the hospital with a 3-week history of spiking diurnal fevers ranging from 101.7° to 104.5° F. He was alert but irritable and refused to walk. His past history was unremarkable, he had not traveled, and his immunizations were up to date.
Physical exam findings were normal except for shoddy inguinal lymphadenopathy bilaterally, mild synovitis bilaterally in the ankles, slightly decreased extension of the left wrist, and pain with motion of the left ankle or wrist. He had a faint macular rash over his chest,
MRI of both ankles showed mild effusion with no significant synovial thickening. Bone marrow aspiration results suggested an acute inflammatory process. Clinicians could find no neoplastic lesions. A gallium scan showed increased uptake in the right distal thigh above the knee joint.
A multicystic, loculated lesion consistent with a formed abscess was seen on an MRI of the thigh. Physicians opened and drained the abscess, and the child was treated with antibiotics.
The abscess exudates were negative on Gram stain, culture, and acid-fast stain. The pathology specimen was consistent with a simple abscess and reactive inflammation in the muscle and periosteum. There was no direct evidence of infection in either the bone or muscle.
Despite extensive antibiotic therapy, the child continued to spike fevers up to 104°F. Viral studies and tuberculosis tests were negative. The persistent fevers, lack of an infectious process, and evidence of joint involvement led clinicians to consider systemic JIA more closely. The child's serum ferritin level increased from 500 ng/mL to 1,583 ng/mL; markedly elevated serum ferritin is a common finding in systemic JIA.
When physicians started the NSAID naproxen (Naprosyn), the fevers decreased to around 101°F. Subsequent steroid treatment significantly reduced symptoms, and the fevers resolved. A repeat gallium scan showed mild residual uptake in the right thigh and periosteum, and symmetrical uptake in both ankles. Repeat surgical exploration of the abscess found reaccumulation of purulent material.
The patient went home with a diagnosis of systemic JIA and a lower regimen of steroids, and the fevers returned. He currently is being treated with methotrexate and a weaning dose of prednisone.
MRI showed a multicystic, loculated lesion along the left side of the bone that was consistent with a formed abscess. The exudates were negative for infection. Photos courtesy Dr. Elizabeth C. Chalom
