Investigation of acute monoarthritis (summary)

This is a basic article for medical students and other non-radiologists

Acute monoarthritis describes the acute onset of arthritis affecting a single joint. It may be a large weight-bearing joint, or a smaller joint such as an interphalangeal joint, the great toe metatarsal-phalangeal joint, or an elbow. 

Assessment

History and examination of the joint will narrow the differential diagnosis. Broadly, this differential includes:

• septic arthropathy, e.g. bacterial septic arthritis
• inflammatory arthropathy, e.g. rheumatoid arthritis, juvenile idiopathic arthritis, psoriatic arthritis
• systemic disease, e.g. systemic lupus erythyematosus, Behcet's, reactive arthritis
• crystal arthropathy, e.g. gout
• bone/cartilaginous disease, e.g. osteoarthritis
• trauma, e.g. traumatic effusion/hemarthrosis

Eliciting a history of recent trauma, systemic disease or recent/current infection significantly reduces the size of the list of differentials. Recognizing that there is erythema around a hot, swollen joint also limits the differential.

Investigation

Blood tests including inflammatory markers and a full blood count are part of a standard workup. Radiology is helpful to make an assessment of the underlying bone. Ultrasound can be useful to confirm whether there is a joint effusion and how large it is.

If there is an effusion, it may sometimes be helpful to take a sample of joint fluid. This is particularly useful if there is a concern for infection, or where there is suspicion of a crystal arthropathy.

Common pathology

• septic arthritis
• gout
• psoriatic arthritis