- Welcome back Rheumatology fans, we are all about imaging and Psoriatic Arthritis this week following a heads up from the wonderful Chris Martey on twitter about a paper tha discusses this in fantastic detail. I have pulled out what I believe to be the salient points for this blog.
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PLEASE REMEMBER – THIS BLOG IS NOT A REPLACEMENT FOR CLINICAL REASONING, IF YOU ARE UNSURE GET ADVICE
Introduction
Psoriatic Arthritis (PsA) falls under the umbrella term of Spondyloarthritis. It is very common in those with Psoriasis with up to 30% developing an inflammatory arthritis. Other types of arthritis can still occur in this group and understanding differential diagnosis is important. I have some more blogs on the topic:
The paper has a great overview as well of PsA and I would definitely set aside some time to read it! I am going to point out what I think are the important parts regarding imaging for those of us outside of Rheumatology departments in MSK clinics and the like.
XRAYS
Xrays can be useful in PsA, imaging of the hands and feet may reveal erosions and co-existing new bone formation, these could occur in the more proximal joints (MCPJs and MTPJs) as well as the more peripheral joints (IPJs and DIPJs) even in early disease where Rheumatoid Arthritis is much more likely to cause erosions proximally and Osteoarthritis to cause new bone formation and sometimes erosions peripherally.
Axially similar changes occur to Ankylosing Spondylitis, sclerosis, erosions and or fusion of the SIJs and Syndesmophytes in the spine. Both SIJs can be affected but unilateral findings are suggestive of PsA.
Not all people with PsA will go on to develop structural changes and it is less common in early disease, couple that with a radiation dose and it makes xrays drop down the list of priorities outside of the Rheumatology clinic. It may play a role in some clinics with immediate access to radiographs compared to long waits for other modalities. Be especially considerate with younger patients.
MRI
I would utilise Axial MRI in the same way as for all Axial Spondyloarthritis presentations, requesting Spondyloarthritis protocol sequences I wrote a blog HERE
It is also possible to use MRI peripherally and might be a good option if there are lot of areas involved in the hand or foot (multiple digit dactylitis for example). This would visualise soft tissue inflammation such as synovitis, enthesitis and tenosynovitis as well as bone marrow oedema but be aware these findings are not specific to PsA.
A common downside to MRI is wait times for access, consider if clinically there is enough evidence to require a referral to Rheumatology without the imaging. This is less of a concern where waiting times are minimal.
ULTRASOUND
Ultrasound is quick and often of easy access potentially available in the Musculoskeletal clinic. Visualisation of Synovitis, enthesitis and tenosynovitis is all possible and flexor tenosynovitis is the major contributor to dactylitis. These findings can aid significantly in the differential diagnosis process without exposing the patient to radiation or prolonged wait times. Outward referral to a radiology department may however succumb to the same issues as MRI.
Recommendation
I would utilise imaging for PsA in a musculoskeletal clinic in this order of preference. I would not delay a rheumatology referral if there are good suspicions of inflammatory arthropathy waiting for imaging results, this reasoning process may change in the situation of very long specialist waiting lists.
Ultrasound – Especially if available immediately in the clinic (often referred to as “point of care”
MRI – If the wait times for Ultrasound are longer than MRI and/or axial imaging is needed
Xray – Older patient with long duration (years) of symptoms AND immediately/very quickly accessible compared to MRI/Ultrasound/Rheumatology referral.
I hope you have found this blog useful, I look forward to hearing feedback, different things you do in clinic or requests for further blogs 🙂 Thank you for reading.
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