Diagnosis and treatment
The MRI findings were in keeping with acute osteomyelitis and periostitis of the distal right humerus. Secondary inflammation of the elbow joint synovitis and soft tissue cellulitis is likely present as well.
No definite drainable abscess is present. Her blood culture identified the presence of Staphylococcus aureus. Intravenous cefazolin, 260 mg every 8 hours, was initiated. A peripherally inserted central catheter (PICC) line was placed under anesthesia before hospital discharge.
Clinical features: Acute osteomyelitis in children is primarily a clinical diagnosis based on the rapid onset and localization of symptoms. Acute hematogenous osteomyelitis results from bacteremic seeding of bone. Children are most often affected because the metaphyseal or growing regions of the long bones are highly vascular and susceptible to even minor trauma. More than one-half of cases of acute hematogenous osteomyelitis in children occur in patients aged less than 5 years.1
Osteomyelitis is an infection localized to bone. Microorganisms, predominantly bacteria that enter the bone hematogenously, usually cause it. Other pathogenetic mechanisms include direct inoculation, such as trauma or surgery, or local invasion from a contiguous infection, such as decubitus ulcer, sinusitis, or periodontal disease.
Children with hematogenous osteomyelitis usually present acutely with fever, constitutional symptoms such as irritability and decreased appetite or activity, and focal findings of bone inflammation such as warmth, redness over the infection site, point tenderness, and limited function. It should be noted, however, that initial symptoms can be nonspecific in children of all ages (eg, malaise and low-grade fever). Once the infection becomes established in bone, the symptoms are more localized.2
In a systematic review by Dartnell J et al3 that included more than 12,000 children with acute and subacute osteomyelitis, presenting features included pain (81%), reduced range of motion (50%), localizing signs and symptoms (70%), reduced weight bearing (50%), and fever (82%).
Hematogenous osteomyelitis generally occurs at only one site. Long or tubular bones are affected more frequently than nontubular bones, such as flat, irregular, and sesamoid bones. The sites of involvement in children in order of most common to least common include the femur (27%), tibia (26%), pelvis (9%), feet (8%), humerus (8%), radius/ulna (5%), vertebrae (4%), fibula (4%), and the hands (2%).3
Laboratory features: Elevations in peripheral leukocyte count in osteomyelitis are variable and nonspecific. Findings from the systematic review by Dartnell J et al3 indicated that the leukocyte count was elevated in 36% of patients at the time of presentation. The leukocyte count tends to be higher and take longer to normalize in children with osteomyelitis caused by methicillin-resistant S. aureus (MRSA), group A Streptococcus, or Streptococcus pneumoniae infection, and in children with concomitant septic arthritis.
Elevation of CRP occurs in most children with osteomyelitis. In the review by Dartnell et al3, CRP was elevated in 81% of children at the time of presentation, peaked on day 2, and normalized over 1 week. In one of the studies in their analysis, the mean CRP level was 87 mg/dL at the time of presentation.
Elevation of the ESR to greater than 20 mm/h occurs in most children with osteomyelitis. Dartnell et al3 found that ESR was elevated in 91% of children at the time of presentation, peaked on days 3 to 5, and normalized over 3 or 4 weeks; the mean ESR was 51 mm/h at the time of presentation.4
Imaging modalities: A plain radiograph has a sensitivity of 16% to 20% and a specificity of 80% to 100%. However, a plain radiograph will not show abnormal findings at the onset of symptoms, and a normal radiographic result does not exclude osteomyelitis.
MRI is the preferred imaging modality to establish the diagnosis of osteomyelitis; it has a sensitivity of 80% to 100% and a specificity of 70% to 100%. This test identifies early changes in the bone marrow cavity and the location and extent of osteomyelitis. Therefore, osteomyelitis is unlikely if the MRI result is normal. The disadvantage of MRI is that young children may require sedation or anesthesia for an optimal study result.
Computed tomography (CT) only has a sensitivity of 67% and a specificity of 50% for osteomyelitis. A disadvantage of CT is radiation exposure.
Ultrasonography is useful to evaluate fluid collections in the adjacent structures, but this imaging modality does not penetrate the bone cortex. Therefore, it has a low sensitivity and specificity of 55% and 47%, respectively.5
Epidemiology: In high-income countries, acute osteomyelitis occurs in approximately 8 out of 100,000 children per year, but it is considerably more common in low-income countries. Boys are affected twice as often as girls, and hematogenous osteomyelitis is more common in children than adults.
More than one-half of pediatric cases occur in children aged younger than 5 years, and one-quarter of cases occur in children aged younger than 2 years. Osteomyelitis is uncommon in infants aged younger than 4 months without underlying risk factors.
Unless acute osteomyelitis is diagnosed promptly and treated appropriately, it can be a devastating or even fatal disease with a high rate of sequelae, especially in resource-poor countries where patients present with advanced disease and survivors often have complications that are serious and long lasting.5