Investigation of acute monoarthritis (basic)

Dr Jeremy Jones et al.

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. 

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. SLE, Behcet's, reactive arthritis
  • crystal arthropathy, e.g. gout
  • bone/cartilaginous disease, e.g. osteoarthritis
  • trauma, e.g. traumatic effusion/haemarthrosis

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

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.

  • septic arthritis
  • gout
  • psoriatic arthritis
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