Arthritis refers to inflammation of a joint or joints and can result from a variety of processes. The end result if not treated is joint damage.
A single swollen joint - Key causes include
- Infection (and reactive arthritis) - bacterial and mycobacterial (including Tuberculosis - TB)
- Trauma (including non-accidental injury)
- Inflammatory (Oligoarticular onset Juvenile Idiopathic Arthritis or arthritis related to inflammatory bowel disease)
- Haemarthrosis (trauma or bleeding disorder)
In the absence of trauma or infection, Juvenile Idiopathic Arthritis is the most likely; in contrast to adults with a single swollen joint - children very rarely get gout ! Clinical assessment and presence or absence of red flags are most important when considering the differential diagnosis. Careful use of investigations will invariably confirm or refute potential causes. In endemic areas or in a child with risk factors (immunosuppression), TB must always be considered with a single swollen joint. In such endemic areas - the corollary however is not 'blind' anti-tubercular treatment for chronic monoarthritis.
Children with septic arthritis appear unwell, are febrile and the affected joint and limb held still as they have severe pain with joint movement. Septic arthritis usually occurs in large joints, generally involving a single joint.
Reactive arthritis is usually monoarticular or less commonly oligoarticular (up to 4 joints) and follows bacterial infection in the gut (Salmonella, Shigella, Campylobacter, Yersinia). In older children and adolescents, consider sexually acquired infection (Chlamydia, gonorrhoea). The potential for sexual abuse needs to be considered with sexually acquired infection in children and adolescents. Poncet's disease is a reactive arthritis secondary to TB.
Lyme disease (a reactive arthritis due to Borrelia burgdorferi and transmitted infection by ticks) is suggested by the presence of an oligoarthritis, after travel to an endemic area - the classic history of a tick bite, or rash (erythema chronicum migrans) may not be prominent.
Mycobacterial disease (including TB) must be considered in the context of the unwell child with joint pain or swelling and especially in the context of immunosuppression (through disease or treatment). Multisystem disease (such as Juvenile Systemic Lupus Erythematosus) is unlikely to present with a single swollen joint.
Inflammatory bowel disease associated arthritis may precede or follow the gastrointestinal features.
Multiple swollen joints: These are unlikely to be due to infection (other than some forms of reactive arthritis) or trauma and makes a systemic disease more likely.
Key conditions include
- Juvenile Idiopathic Arthritis is likely but malignancy (leukaemia) has to be excluded.
- Metabolic conditions (osteomalacia / rickets)
- Chromosomal conditions (eg Downs syndrome associated arthritis)
- Inherited metabolic conditions (eg Mucupolysaccharidoses)
- Skeletal dysplasias
Multisystem disease such as Juvenile Systemic Lupus Erythematosus or Juvenile Dermatomyositis tend to cause joint pain (arthralgia) rather than joint swelling. Children with chromosomal conditions may also be prone to developing joint problems, including hypermobility and inflammatory arthritis. Inherited metabolic conditions (including mucopolysaccharidoses) may manifest with complex multisystem involvement including joint abnormalities due to contractures or sometimes hypermobility. Skeletal dysplasias may be suggested by short stature, joint contractures and pain often with a positive family history.
Rheumatic fever (a form of reactive arthritis that follows pharyngeal streptococcal infection). Rheumatic fever is more common in countries such as India compared to the UK (although there is a significant declining trend in incidence observed in India). The arthritis can involve many joints, often large joints and flitting from joint to joint.
Post viral arthritis such as with rubella infection can involve many joints whereas after chicken pox (varicella) can be an oligo-arthritis or polyarthritis.
The photograph below shows a swollen right knee (due to oligoarticular JIA).