People with dactylitis have more severe psoriatic arthritis

Dactylitis is linked to increased disease burden in psoriatic arthritis, and might be a useful sign to identify people at risk.

INTRODUCTION
Psoriasis is a chronic inflammatory skin condition that causes redness and scaling. Many people with psoriasis also have psoriatic arthritis (often shortened to PsA). In psoriatic arthritis, the disease causes pain and swelling in people’s joints, resulting in joint damage and disability. Psoriatic arthritis can affect joints in the arms, hands, legs, feet, as well as the spine. At least one-third of people with psoriatic arthritis have swelling in their fingers or toes. People sometimes refer to this specific type of swelling as “sausage” toes or fingers. The official medical term is dactylitis.

There are many different types of treatments available for people with psoriatic arthritis, including a group of medicines called disease-modifying antirheumatic drugs (shortened to DMARDs).

WHAT DID THE AUTHORS HOPE TO FIND?
The authors wanted to find out whether having dactylitis has an impact on the disease burden and outcomes compared to people who have psoriatic arthritis without dactylitis.

WHO WAS STUDIED?
The study looked at 177 people with early psoriatic arthritis. Everyone taking part had been diagnosed with psoriatic arthritis within 12 months of study recruitment, and had not yet started to take any DMARD treatments.

HOW WAS THE STUDY CONDUCTED?
This was a cross-sectional study, which means that the researchers simply observed and recorded information about the people taking part. A study of this type is used to compare different groups of people at a single point in time, without changing any variables.

The authors used the information collected to compare clinical outcomes and disease severity between
two groups: those with and without dactylitis at their first visit to the rheumatology clinic. This included taking blood tests to look for signs of inflammation, and performing ultrasound scans to look inside the joints. Everyone also had clinical examinations to see if they had swollen or tender (sore) joints.

WHAT WERE THE MAIN FINDINGS OF THE STUDY?
The main finding was that people with dactylitis had a greater burden of disease. This included having higher levels of C-reactive protein (often shortened to CRP) – a blood test marker that means there is inflammation present in the body. The people with dactylitis also had more swollen joints (even after excluding the fingers and toes affected by dactylitis), and ultrasound images showed there was more joint inflammation and bone damage.

These findings suggest that dactylitis in people with early psoriatic arthritis is a sign of having a more aggressive type of disease. People with this feature could have worse outcomes over time, which means that dactylitis should not be ignored.

ARE THESE FINDINGS NEW?
Yes. This is the first study to show that there is an increased disease burden in people with early psoriatic arthritis and dactylitis compared with those with psoriatic arthritis but no dactylitis. Importantly, this was not only in joints affected by dactylitis.

WHAT ARE THE LIMITATIONS OF THE STUDY?
The study does have some limitations. For example, although the authors found differences in joint inflammation and bone damage using the ultrasound imaging, they could not find a significant difference for another common feature of psoriatic arthritis called enthesitis (inflammation of tendons and ligament insertions into bone).

WHAT DO THE AUTHORS PLAN TO DO WITH THIS INFORMATION?
The authors are planning another study in the same group of people to see how their disease progresses over time. It is hoped this will improve the understanding of the disease – and help improve care for people with psoriatic arthritis.

WHAT DOES THIS MEAN FOR ME?
If you have psoriatic arthritis and swelling of a whole finger or toe you should tell your doctor. This will help you get any necessary investigations and treatment as early as possible.

If you have any concerns about your disease or its treatment, you should talk to your doctor.

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Date prepared: March 2022
Summary based on research article published on: 10 December 2021
From: Dubash S, et al. Dactylitis is an indicator of a more severe phenotype independently associated with greater SJC, CRP, ultrasound synovitis and erosive damage in DMARD-naive early psoriatic arthritis. Ann Rheum Dis 2022;81:490–5. doi:10.1136/annrheumdis-2021-220964

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