In a new Case Record of the Massachusetts General Hospital, a 9-month-old girl presented with a 2-month history of recurrent fevers. Examination revealed fever and tachycardia and was otherwise normal; chest and abdominal imaging studies showed no evidence of infection. Additional diagnostic tests were performed.
Septic arthritis is a pediatric orthopedic emergency.
• What is the definition of fever of unknown origin in children, and how often is infection the cause?
While the terms recurrent fever and fever of unknown origin are often used interchangeably, and the differential diagnosis is similar for both, there are specific definitions for fever of unknown origin. In 1961, fever of unknown origin was defined as a temperature of greater than 38.3 degrees C (101 degrees F) “on several occasions,” a duration of illness of greater than 3 weeks, and no cause of fever despite 1 week of inpatient investigation. Over subsequent decades, there have been amendments to the definition and proposals for different categories. Although there is no single generally accepted definition, a working definition would include a temperature of greater than 38.3 degrees C (101 degrees F), a duration of illness of at least 1 week, and a negative initial outpatient or inpatient evaluation, which includes history taking, physical examination, and routine laboratory testing. The differential diagnosis of fever of unknown origin is broad. A systematic review of 18 studies performed between 1950 and 2010 involving children who were evaluated for fever of unknown origin showed that half had infections, fewer than 10% had collagen vascular disease or malignant tumors, and almost one quarter had no diagnosis.
• What clinical features can help to distinguish septic arthritis from toxic synovitis?
Features that can help in distinguishing septic arthritis from toxic synovitis in children are an inability to bear weight, fever, and elevations of the erythrocyte sedimentation rate (>40 mm per hour) and white-cell count (>12,000 per cubic millimeter).
Morning Report Questions
Q: What are some of the microorganisms identified in septic arthritis affecting young children?
A: The microbiologic features of septic arthritis can vary depending on age, immunization history, possible exposures, and the presence of chronic conditions. Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) are the most common causes in all age groups. Of the types of streptococci, group B streptococcus is most common in infants younger than 3 months of age, group A streptococcus is most common in infants older than 3 months of age, and Streptococcus pneumoniae is most common in infants older than 3 months of age who are not immunized. The gram-negative bacillus Kingella kingae is increasingly identified in patients with septic arthritis who are between 3 months and 3 years of age.
Q: What long term sequelae may result from septic arthritis in children?
A: Septic arthritis is a pediatric orthopedic emergency. Early diagnosis and expedited treatment are critical for a satisfactory outcome. Although bone has the ability to repair itself, articular and epiphyseal cartilage does not. In addition to the effect of the infection on the child’s general health, there is a risk of considerable damage to the joint. Potent proteolytic enzymes are released in the joint directly from the bacteria and host tissue (i.e., synovial cells and chondrocytes) in response to the infection; these enzymes destroy the hyaline cartilage. Some studies have shown that cartilage destruction begins within 6 to 8 hours after bacterial colonization. Capsular distention, which occurs as a result of the effusion, coupled with muscle spasm, which occurs as a result of pain, can lead to a pathological dislocation of the joint and necessitate the application of a brace. Increased intraarticular pressure, which occurs as a result of the pus accumulation, can lead to avascular necrosis of the femoral head. All these features can lead to limb-length discrepancy, proximal femoral deformity, acetabular dysplasia, and joint stiffness and may lead to degenerative arthritis in the long term.
Figure 3. Imaging Studies of the Pelvis and Hips.