Single joint arthritis
A single swollen joint has several potential causes.
Key causes include:
- Infection (and reactive arthritis) - bacterial and mycobacterial.
- 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 (JIA) is the most likely; in contrast to adults with a single swollen joint - children rarely get gout!
Assessment and the presence of red flags are most important when considering serious conditions such as infection, malignancy or non-accidental injury.
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.
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 can affect just one joint (or occasionally multiple joints) and follows bacterial infection in the gut (Salmonella, Shigella, Campylobacter, Yersinia). In older children and adolescents, it is considered a sexually acquired infection (Chlamydia, gonorrhoea); Safeguarding concerns may need to be considered.
Lyme disease (a reactive arthritis due to Borrelia burgdorferi and transmitted infection by ticks) is suggested by the presence of an arthritis, after travel to an endemic area - the classic history of a tick bite, or rash (erythema chronicum migrans) may not be prominent.
Mycobacterial disease 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 Systemic Lupus Erythematosus) is unlikely to present with a single swollen joint.
Inflammatory bowel disease associated arthritis may precede or follow the gastrointestinal features.