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Single swollen joint

A single swollen joint has several potential causes

Key causes include

  • Infection (and reactive arthritis) - bacterial and mycobacterial (including TB)
  • Trauma (including non-accidental injury) 
  • Inflammatory (Oligoarticular onset Juvenile Idiopathic Arthritis or arthritis related to inflammatory bowel disease)
  • Haemarthrosis (trauma or bleeding disorder) 
  • Malignancy 

In the absence of trauma or infection, Juvenile Idiopathic Arthritis (JIA) is the most likely; in contrast to adults with a single swollen joint - children 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. 

The onset, progress and the presence of extra articular features including fever, red eyes, urethritis, preceding diarrhoea or sore throat often guides the clinician to the correct diagnosis.

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.

The photograph below shows an inflamed right shoulder due to septic arthritis.

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, it is considered to be a sexually acquired infection (Chlamydia, gonorrhoea). The potential for sexual abuse needs to be considered with sexually acquired infection in a child or adolescent. 

The photograph shows a swollen knee in Oligo-articular JIA 

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 Tuberculosis - 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.

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