Imaging

The approach to investigations must always focus on making an accurate diagnosis, planning management or monitoring of the disease. 

Imaging is useful but certain tests may need sedation in young children.

It is important to plan investigations to gain the most information and minimise radiation exposure or need for sedation.

• Radiographs or Computerised Tomography or Radionuclide bone scans result in radiation exposure.
• Ultrasound scanning is increasingly used, does not result in radiation exposure or require sedation but is operator dependent.
• Magnetic Resonance Imaging may need sedation.
• Densitometry is used to assess bone density. 

Children may need sedation to enable imaging to take place.  

• Musculoskeletal ultrasound (MSUS) is sensitive to early changes in JIA and helps to identify which structures are involved in a clinically swollen joint.
• Ultrasound can differentiate between joint effusions, synovial hypertrophy, synovitis, enthesitis, tendonitis and tenosynovitis.
• Ultrasound is cheap and easy to perform and is well tolerated by most children, without the need for general anaesthesia. 
• MSUS findings are operator dependent; standardising procedures and comparing findings between observers is important. 

• Radiographs are usually normal in early inflammatory arthritis (JIA). Although plain radiographs may reveal soft tissue swelling around joints or demonstrate bony erosions, radiographs are an insensitive tool for the diagnosis of acute synovitis or erosive joint damage. Ultrasound scanning or Magnetic Resonance Imaging are preferable.
• Plain radiographs can be used in the initial investigation of children with bone pain or arthritis.
• The presence of periosteal reaction suggests the possibility of bony infection or malignancy.
• Radiographs of the knee should include the long bones above and below in the context of persistent knee pain - bone tumours commonly arise in the distal femur or proximal tibia. 
• An anterior-posterior view of the hand and wrist can be a useful screening tool in the investigation of metabolic bone disease (for example rickets).
• It is often useful to compare both sides (e.g., hip radiographs) to exclude pathology. Frog views should be requested to detect subtle changes of Slipped Upper [Capital] Femoral Epiphysis.

• Magnetic Resonance Imaging (MRI) is very sensitive to early changes in JIA and can differentiate between bony and soft tissue lesions.
• MRI is not always available, is expensive and requires sedation or general anaesthesia in younger children.
• Intravenous contrast, such as gadolinium, is important to the assessment of synovitis. 
• In the context of inflammatory back pain, MRI of the spine and sacroiliac joints (with gadolinium) is warranted; radiographs are very difficult to interpret in adolescents and the radiation exposure is considerable.