Psoriatic Arthritis, Rheumatoid Arthritis Cause Similar Hand Impairment, but So Does Psoriasis

Patients with psoriatic arthritis (PsA) and rheumatoid arthritis (RA) experience equivalent declines in hand function, according to a new study, but investigators also found that psoriasis itself causes similar impairment of the hands.

The study, published in ACR Open Rheumatology, raises new questions about links between psoriasis and arthritis.

Both PsA and RA have well-documented impacts on patients’ physical functioning, but less has been published related to how the loss of hand function experienced by patients with RA compares with that of other diseases, according to corresponding Anna-Maria Liphardt, PhD, of the Friedrich-Alexander University Erlangen Nürnberg and University Clinic Erlangen, in Germany, and colleagues.

“The impact of inflammatory arthritis on hand function has mainly been studied in RA,” they said, “and studies comparing hand function in these diseases are sparse.”

Liphardt and colleagues therefore decided to comprehensively evaluate hand function in PsA and RA side by side, by looking at objective strength measures and also patient perceptions of hand function. In addition to comparing these measures in the 2 disease categories, the authors also compared them with healthy controls.

In the study, 299 subjects were enrolled, split nearly evenly between patients with RA (101 patients), patients with PsA (92 patients), and nonarthritic controls (106 patients). The nonarthritic patient arm was made up of 51 patients with psoriasis and 55 healthy controls.

The patients were assessed using a number of measures. A hand dynamometer was used to measure isometric grip strength. The Moberg-Picking-Up Test (MPUT) was used to assess fine-motor skills, and patients were also timed to see how long it took them to move 12 small items from a table into a box with their eyes opened. Lastly, patients were asked to rate their own hand function using the Michigan Hand Questionnaire (MHQ). Data were taken for both hands, but the investigators noted which hand was a patient’s dominant hand.

The investigators found that sex, age, disease group, and hand dominance all affected hand function. However, PsA and RA appeared to have similar influences on hand function, and in both cases the impact was greater for women than men. 

“We found that the impact of disease on hand function is particularly pronounced in older subjects, suggesting that younger individuals are better in functionally compensating their diseases,” they said. “This may be caused by generally better muscular performance and neuromuscular interaction in younger individuals, but also by disease management of RA and PsA in the last two decades.”

However, the authors also reported something they did not expect: Patients with psoriasis were experiencing significantly altered hand function.

“Although these patients did not show any clinical signs of PsA, hand function was clearly impaired and mirrored that in patients with RA and PsA but not in healthy controls,” they said.

Liphardt and colleagues said the finding suggests psoriasis patients “exhibit a functional arthritis-like phenotype.”

“Such observations back concepts that patients with psoriasis show an altered stress response not only in the skin but also in the musculoskeletal structures,” they said.

The investigators added that it is possible that functional changes in patients with psoriasis might be indicative of a more pronounced progression to PsA, but they said the question would need to be investigated with further studies.

Reference

Liphardt AM, Manger E, Liehr S, et al. Similar impact of psoriatic arthritis and rheumatoid arthritis on objective and subjective parameters of hand function. ACR Open Rheumatol. 2020;2(12):734-740. doi:10.1002/acr2.11196