Differential Diagnosis for the 2-year-old Child with Leg Pain
Single Most Likely Diagnosis
- Septic Arthritis: The high nucleated cell count (52,000/μL) with a predominance of neutrophils (95%) and the presence of a significant number of red blood cells (RBC = 375,000/μL) in the synovial fluid, along with the clinical presentation of pain, tenderness, edema, and refusal to walk, strongly suggests septic arthritis. The yellow and turbid appearance of the fluid further supports this diagnosis, as it indicates the presence of pus.
Other Likely Diagnoses
- Traumatic Hemarthrosis: The presence of a high RBC count in the synovial fluid could also suggest traumatic hemarthrosis, especially if the child had a recent injury. However, the high nucleated cell count with a predominance of neutrophils leans more towards an infectious process.
- Transient Synovitis: This condition is a common cause of hip pain in children and can present with similar symptoms. However, the fluid analysis would typically show a lower nucleated cell count and a higher proportion of mononuclear cells.
Do Not Miss Diagnoses
- Osteomyelitis: Although the primary presentation is in the joint, osteomyelitis (infection of the bone) could potentially cause similar symptoms and must be considered, especially if there's a history of trauma or if the child does not respond to treatment for septic arthritis.
- Malignancy (e.g., Leukemia): Though less likely, malignancies can cause joint pain and effusions. The presence of a high nucleated cell count could potentially be misinterpreted, and a differential diagnosis including malignancy must be considered to avoid missing a potentially life-threatening condition.
Rare Diagnoses
- Lyme Arthritis: This condition can cause arthritis in children, particularly in endemic areas. The synovial fluid analysis might show a lower cell count compared to septic arthritis, but it's a consideration in the appropriate clinical context.
- Juvenile Idiopathic Arthritis (JIA): While JIA can cause joint pain and effusions, the fluid analysis typically shows a lower nucleated cell count with a predominance of mononuclear cells, making it less likely given the current fluid analysis results.