Arthritis refers to inflammation of a joint or joints that can lead to joint damage in the absence of diagnosis and treatment.
Arthritis can affect a single joint or multiple joints and can be a manifestation of many systemic conditions and processes (including infection, malignancy, connective tissue diseases, genetic conditions and other metabolic diseases).
Clinical assessment and the presence or absence of red flags are most important when considering the differential diagnosis. The use of investigations and their judicious interpretation will help to confirm or refute potential causes.
- In the absence of trauma or infection (or Acute Rheumatic Fever in high risk populations), Juvenile Idiopathic Arthritis (JIA) is the most likely cause of a single swollen joint. In contrast to adults with a single swollen joint, children very rarely get gout.
- Mycobacterial disease (including Tuberculosis [TB]) must always be considered with a single swollen joint in endemic areas or in a child with risk factors (immunosuppression or risk of exposure or with co-existent Human Immunodeficiency Virus). The corollary however, is that not all cases of chronic monoarthritis are due to TB.
- Inflammatory bowel disease associated arthritis may precede or follow the gastrointestinal features and usually presents with a single joint arthritis or asymmetrical arthritis affecting several joints or with sacroiliitis.
- There are many causes including systemic diseases such as rheumatic disease (JIA, connective tissue diseases, autoinflammatory diseases / periodic fevers), genetic diseases (e.g., sickle cell disease, Down's syndrome arthritis) and some metabolic conditions.
- Infections (e.g., Arboviruses and Acute Rheumatic Fever - ARF) and some forms of reactive arthritis cause multiple joint arthralgia or arthritis. ARF tends to affect multiple joints although a monoarthritis is also possible.
- Connective tissue diseases such as Juvenile Systemic Lupus Erythematosus, Juvenile Dermatomyositis and Scleroderma are key multisystem conditions that tend to cause joint pain (arthralgia) and functional limitation (through stiffness); joint swelling may be less than in JIA.
- Children with genetic or chromosomal conditions (such as Downs syndrome) may also be prone to developing a spectrum of joint problems, ranging from hypermobility to inflammatory arthritis. It is important that the child is assessed carefully as the functional problems may be falsely regarded as being due to the underlying genetic condition - and inflammatory arthritis may be missed.
- Inherited metabolic conditions (including mucopolysaccharidoses) may manifest with complex multisystem involvement including joint restriction (due to contractures or abnormal skin thickening) and / or joint laxity / hypermobility.
- Skeletal dysplasias may result in bone or joint pain and deformity. They can be suggested by other features such as short stature, joint contractures and family history.