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Psoriatic Arthritis: Neuropathic Pain and Fibromyalgia Links

October 29, 2020
Study examines the crossover between widespread pain and PsA, suggesting that clinicians assess for differential diagnoses when appropriate.

A PPM Brief

Traditionally, pain in patients with rheumatic disease has been characterized as nociceptive, said Deeba Minhas, MD, a rheumatologist at the University of Michigan, and this would imply that managing the inflammation would manage the pain. However, many individuals with rheumatic conditions experience chronic pain even when their disease activity is under control.1,2

“We now understand that rheumatic pain is more complicated. It consists of nociceptive pain, characterized by tissue damage and inflammation, and neuropathic pain, characterized by nerve involvement,” said Dr. Minhas. Psoriatic arthritis (PsA), in particular, poses its own challenges as it is a much more heterogenous disease compared to rheumatoid arthritis, she explained.

To better understand pain in association with rheumatic conditions, a team of researchers in Italy took a deep dive into the prevalence and clinical variables of neuropathic pain in patients with PsA. They found some intriguing results.

Rheumatic pain is complicated – it consists of nociceptive pain, characterized by tissue damage and inflammation, and neuropathic pain, characterized by nerve involvement – and PsA in particular poses its own challenges as a more heterogenous disease. (Image: iStock)

Methods

Their study, published in August 2020 in the Journal of Rheumatology, was a cross-sectional evaluation of patients with psoriatic arthritis (PsA) with peripheral joint involvement.2

Participants were selected from the outpatient centers of three rheumatology clinics in Italy. Included were adult patients with PsA with peripheral joint involvement (patients with sacroiliitis or axial skeleton involvement were not excluded). Diagnoses were made using the Classification Criteria for PsA, or CASPAR. Subjects were excluded from the study if they had active skin conditions other than psoriasis, inflammatory comorbidities, or co-existing neuropathic conditions. A final total of 118 patients were selected (n = 118).

An experienced rheumatologist performed a musculoskeletal examination of each participant, with focus on the subject’s functional status and neurological pain features. The number of tender joints (0 to 68) and enthesitis were assessed using the Leeds Enthesitis Index (LEI).

A second rheumatologist administered questionnaires to the patients. This physician was blinded to the results of the physical examinations. Demographic data, additional comorbidities, ongoing treatments, and inflammation markers were recorded.

Researchers also used a 0 to 10 numerical rating scale and C-reactive protein levels to calculate the PsA-specific disease activity index (DAPSA). The Health Assessment Questionnaire-Disability Index (HAQ-DI) was used to determine patients’ difficulty in performing daily activities. For assessing neuropathic pain, researchers used the painDETECT questionnaire (PDQ) which scores pain on a scale from 1 to 38.

Results

A PDQ of greater than or equal to 19 was found in more than 25% of the subjects. Roughly 17% scored between 13 and 18 on the PDQ, indicating a substantial burden of neuropathic pain.

Of the variables examined, the only statistically significant correlation with neuropathic pain in the patients studied was the presence of fibromyalgia syndrome (FM). FM was diagnosed in 30 of the participants (25%), 28 (93%) of which were women. Of these 30, 25 reported taking medications for neuropathic pain, including gabapentinoids, duloxetine, and tapentadol.

Based on these results, the researchers decided to compare the PDQ scores of the patients without FM to those with FM. Their analysis showed that the pain scores of patients with FM and PsA were significantly higher than those without. A second logistic regression analysis excluded patients with FM. In this set of 88 patients, researchers found features that indicated neuropathic pain in only 12 subjects and ambiguous features of neuropathic pain in 17 subjects. Neither disease activity nor joint or skin disease were correlated with the presence of neuropathic pain.

Practical Takeaways

The researchers pointed out in their paper that prior studies have documented a connection between fibromyalgia and neuropathic pain in people with rheumatoid arthritis. However, they noted, there is a lower prevalence of neuropathic pain in individuals with RA than with PsA. They speculated that “the extent and severity of the psoriasis [could possibly] explain this difference.”2

Practically speaking, their findings suggest that clinicians treating complex pain syndromes like fibromyalgia in patients with PsA (and vice versa) should ensure that pain assessments look at differential diagnoses where appropriate. Doing so, the researchers wrote in their final report, may be “increasingly useful to avoid overtreatment with immunosuppressive drugs and using drug therapy appropriate to the pathophysiological mechanisms” behind the pain.2

Dr. Minhas agrees, adding that, “Patients who meet the criteria for fibromyalgia, or have high scores on the fibromyalgia scale (even if they don’t meet criteria) are more likely to respond poorly to peripherally directed interventions.”

 

Last updated on: November 2, 2020
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