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Nail enthesitis offers ‘gateway’ between appendicular system, skeletal PsA
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CHICAGO — Nail enthesitis potentially offers an “intriguing gateway” connecting the appendicular system to the skeletal manifestations of psoriatic arthritis, according to a presenter at the 2019 Interdisciplinary Autoimmune Summit.
“We used to think that the nail just belongs to our dermatology friends, but I think it is a gateway to a friendship,” Gurjit S. Kaeley, MBBS, MRCP, RhMSUS, director of musculoskeletal ultrasound and the rheumatology fellowship program at the University of Florida College of Medicine, told attendees.
According to Kaeley, the key to this gateway lies in one of the two main pathologies of psoriatic nail disease, specifically the kind that affects the nail matrix; here, manifestations of the disease can include nail pitting, leukonychia and lunula red spots. In addition, the more severe nail disease has been associated with more severe psoriasis and psoriatic arthritis, as well as an increased risk for developing psoriatic arthritis, Kaeley said.
The matrix itself is formed by three distinct layers, and the individual parts in the matrix that make up each of those layers, he added.
“Why am I getting so excited about this? It’s because I can see through ultrasound the nail as this nice tri-layer — I can see the nail bed and I can see that as the nail matrix ends, the extensive tendon fibers meet it,” Kaeley said. “I can also see the changes of the nail, the obliteration of the normal tri-layer appearance.”
According to Kaeley, fibers from the extensor slip insert into the base of the phalange and have terminating fibers about the nail matrix and bed.
“We have some great histological data showing that this is perhaps a gateway from the appendicular system to the locomotor system, and indeed nail disease may be a form of enthesitis,” he added. “I think it is very exciting to think about that.”
Kaeley also noted that enthesitis is emerging as a marker of disease activity in PsA, and that enthesitis in PsA is associated with radiographic damage in the peripheral and axial joints, which can be detected through ultrasound and MRI.
He added that enthesitis occurs in approximately 35% to 50% of patients with PsA, and is one of six clinical domains highlighted by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis that should be considered when treating PsA.
“Thinking about enthesitis and looking at it, particularly through imaging, is very exciting, because it’s completely different to what we were taught in fellowship,” Kaeley said. “What we are seeing really stimulates the questions of ‘Why is this happening?’ and ‘Why is this happening where it is happening?’” – by Jason Laday
Reference:
Kaeley GS. Ultrasound Evaluation of Enthesitis in Psoriatic Arthritis. Presented at: Interdisciplinary Autoimmune Summit; April 5-7, 2019; Chicago.
Disclosure: Giles reports consulting fees from Novartis.