What are the potential causes of musculoskeletal pain and swelling in a child?

Differential Diagnosis of Musculoskeletal Pain and Swelling in Children

When evaluating a child with musculoskeletal pain and swelling, prioritize excluding serious pathology—infection, neoplasm, and inflammatory arthritis—before attributing symptoms to benign causes, as joint swelling (not pain alone) is the most reliable indicator of chronic inflammatory disease. 1, 2

Critical Conditions Requiring Immediate Exclusion

Infectious Etiologies

Septic arthritis and osteomyelitis are surgical emergencies that must be distinguished from benign conditions. 1

• Septic arthritis is diagnosed using the Kocher criteria: fever >101.3°F, ESR ≥40 mm/hour, WBC ≥12,000 cells/mm³, and inability to bear weight; meeting all four criteria yields near 100% likelihood of septic arthritis 1
• Elevated C-reactive protein >2.0 mg/dL is an accurate additional predictor 1
• Age-specific distribution matters: children <2 years are more likely to have septic arthritis than osteomyelitis; ages 2-10 favor osteomyelitis slightly; ages 10-18 favor septic arthritis 1, 3
• Definitive diagnosis requires arthrocentesis with culture 1

Osteomyelitis presents with persistent nighttime pain, low-grade fever, decreased range of motion, irritability, localized tenderness, and limping. 1

• Most common in children ages 2-12 years, with 3:1 male predominance 1
• Staphylococcus aureus is the predominant pathogen across all age groups 3
• Age-specific pathogens: Group B streptococcus in neonates, Kingella kingae in children <4 years, Salmonella species in sickle cell disease 3
• Laboratory values typically show leukocytosis, elevated ESR, and elevated CRP 1
• Radiographs are often normal in acute osteomyelitis (<14 days); MRI has 82-100% sensitivity and is the diagnostic modality of choice 3
• Concomitant osteomyelitis and septic arthritis occur in >50% of pediatric cases, particularly in neonates and infants 3

Neoplastic Conditions

Spine neoplasms present with persistent nighttime back pain refractory to conservative management in 25-30% of affected children. 1

• Motor or gait disturbance and neurologic symptoms typically present later 1
• Locally aggressive tumors cause rapid pain intensity increase over short intervals 1
• Benign spinal column tumors include osteochondroma, osteoblastoma, osteoid osteoma, giant cell tumor, and aneurysmal bone cyst 1
• Malignant tumors include leukemia, lymphoma, and rarely metastasis 1
• Intramedullary tumors account for 35-40% of intraspinal tumors; astrocytoma (45-60%) and ependymoma (30-35%) are most common 1

Inflammatory Arthropathies

Juvenile idiopathic arthritis (JIA) is the most common inflammatory etiology involving the spinal column, typically occurring in late childhood and most commonly affecting the cervical spine. 1

• Inflammatory spondyloarthropathy should be evaluated when morning stiffness, systemic symptoms, and family history of autoimmune disease are present 4
• Enthesitis can be evaluated with ultrasound in patients with spondyloarthropathy when radiographic findings are absent, though this is operator-dependent 1
• Autoimmune spinal cord etiologies include acute disseminated encephalomyelitis, neuromyelitis optica spectrum disorders, multiple sclerosis, and transverse myelitis 1

Benign Conditions (After Exclusion of Serious Pathology)

Mechanical/Traumatic Causes

The most common etiologies for pediatric back pain are benign: muscle strain, spondylolysis/spondylolisthesis, and disk herniation. 1

• Spondylolysis is a stress fracture of the pars interarticularis associated with sports involving repetitive spinal hyperextension 4
• Radiographs can identify spondylolysis in up to 24% of children with back pain, particularly when spondylolisthesis is present 4
• MRI lumbar spine without contrast is preferred for suspected spondylolysis with negative radiographs, detecting marrow edema indicating acute stress injury 4

Amplified Musculoskeletal Pain Syndromes

Amplified pain syndromes occur most commonly in pre- to adolescent girls and are characterized by increasing pain over time, allodynia, incongruent affect, disproportional dysfunction, and absence of other causes. 5

• Psychological distress within the child or family is apparent in most cases 5
• Treatment focuses on intensive exercise programs (5 hours daily) with functional aerobic training 5
• After one month, approximately 80% have no pain and are fully functional; another 15% are fully functional with mild or recurrent pain 5

Critical Clinical Pitfall

Isolated musculoskeletal pain without other signs has a strong negative predictive value (0.95) for juvenile rheumatoid arthritis or chronic inflammatory disease. 2

• Joint swelling and gait disturbance are the most likely complaints associated with JRA diagnosis 2
• Neither ANA nor rheumatoid factor evaluations are useful in evaluating children with isolated musculoskeletal complaints 2
• Pain alone should not trigger extensive rheumatologic workup; focus on identifying objective swelling, systemic symptoms, and red flags for infection or neoplasm 2