Once per day, she has a fever associated with a rash. Her temperature is 39°C (102.2°F). On exam, she appears ill and uncomfortable. She has tachycardia, tachypnea, hepatosplenomegaly, and warm, painful swelling of multiple joints. A rub is present on cardiac exam. Salmon-colored macules are present on her back and abdomen.
What is the diagnosis?
A. Parvovirus B19 infection.
B. Lyme disease.
C. Systemic-onset juvenile idiopathic arthritis.
E. None of the above.
The correct answer is “C.” Juvenile idiopathic arthritis (JIA) is a group of chronic diseases causing arthritis of unknown etiology affecting children and adolescents younger than 16 years of age. Arthritis must be present in the same joint for more than 6 weeks to diagnosis JIA. Disorders described by the term JIA are grouped into seven categories. (See Table 7–6 and Figure 7–7.) In Lyme disease, the rash is annular, red, and expands to classically form a bull’s eye (erythema migrans). Lyme arthritis differs from JIA in that joints have large effusions and minimal pain. Malignancy (especially leukemia) mimics JIA. Typically only one joint is involved and pain is severe. Bone pain and pain during the night are red flags for malignancy. Fever is not intermittent and arthritis is transient in parvovirus B19 infections. In this patient, the fever, rash, and arthritis should point you toward the diagnosis of systemic-onset JIA (sJIA). Infection and malignancy are always included in the differential diagnosis for sJIA.