Three Signs Point to a Diagnosis of Psoriatic Arthritis

LOS ANGELES, California — If a patient with psoriasis presents with dactylitis, inflammatory back pain, and/or tendon inflammation, think psoriatic arthritis until proven otherwise.

At the annual fall meeting of the Society of Dermatology Physician Assistants, Amanda Mixon, PA-C, said that psoriatic arthritis (PsA) occurs in 20% to 30% of individuals with psoriasis, “but my guess is that number is higher than that.” Mixon practices at the Colorado Center for Arthritis and Osteoporosis, Longmont, Colorado. Psoriasis usually precedes PsA by 8 to 10 years, and PsA affects both genders equally, usually in the fourth decade of life. Genetic and environmental factors play a role.

On clinical presentation, 95% of patients with PsA have peripheral joint disease in the form of synovitis, tenosynovitis, dactylitis, and/or enthesitis, often asymmetric. “They can have little psoriasis and terrible arthritis, or vice versa,” Mixon said. “They don’t automatically correlate with each other. The one thing that does, though, is nail psoriasis. That will correlate with dactylitis, which is basically an inflamed sausage-like finger or toe, which happens for no apparent reason. That is a classic finding of psoriatic arthritis, a slam dunk. It’s important to refer those patients to a rheumatologist.”

She went on to note that 5% of PsA patients have axial involvement. “Always ask psoriasis patients if they have inflammatory back pain, because some of them will have axial involvement exclusively,” Mixon advised. This is different from mechanical back pain, caused by manual labor or an excessive workout, for example, she noted. “Mechanical back pain gets better with rest. People with inflammatory back pain feel the worst in the middle of the night and in the morning. Inflammatory proteins peak in the middle of the night, so when you wake up you feel stiff. People will often say, ‘I feel like the Tin Man’; they have to work the [kinks] out in the morning. It improves with exercise, but not with rest.”

Mixon said that this is a sign that a patient may have PsA, “So when you see psoriasis patients, ask, ‘How’s your back? Does it wake you up in the middle of the night?'”

Because enthesitis is also common in PsA, Mixon also makes it a point to ask psoriasis patients if they’ve had any tendon problems such as plantar fasciitis or tennis elbow. Inflammation of the distal interphalangeal (DIP) joint is another clinical sign. “Rheumatoid arthritis [RA] is a symmetric disease, but that is not the case with PsA,” she said, so if a patient with an RA diagnosis has DIP involvement, “it’s not RA.”

Patients with PsA can also have asymmetric sacroiliac involvement. “They’ll complain of alternating buttock pain that wakes them up at night,” she said. “That’s an important sign that something inflammatory is going on.”

The CASPAR (Classification criteria for Psoriatic Arthritis) criteria are often used to diagnose PsA, “but in rheumatology, people don’t fit into nice little boxes, so there is a lot of gray,” she said. To meet criteria for PsA on CASPAR, patients must have inflammatory arthritis plus at least three points from the following categories: current skin psoriasis (2 points); a history of psoriasis symptoms, but no current symptoms (1 point); a family history of psoriasis and no current or past symptoms (1 point); nail symptoms, such as pitting, onycholysis, or hyperkeratosis (1 point); a negative rheumatoid factor (1 point); and juxta-articular new bone formation on radiograph (1 point).

Therefore, a patient who presents with a swollen knee or finger and also has psoriasis has almost met the criteria for PsA, said Mixon, who in 2019 cofounded Rheumatology Advanced Practice Providers (RhAPP), a national organization of physician assistants and nurse practitioners in rheumatology. “Even having a family history of psoriasis qualifies as a point.”

Common comorbidities associated with PsA are wide-ranging and include gastrointestinal disorders, steatosis, malignancies, obesity, metabolic syndrome, depression, anxiety, hypertension, cardiovascular disease, and uveitis. “The majority of patients I see with PsA and psoriasis have comorbid depression,” she said. “They’re often overweight and have cardiovascular disease. That’s why it’s so important to get these people on treatment, because with proper treatment, you can mitigate that risk.”

Mixon disclosed that she is a member of the speaker’s bureau for AbbVie, Lilly, Janssen, and Amgen. She is also a consultant for Pfizer, Sanofi, and Novartis.

Society of Dermatology Physician Assistants (SDPA) 19th Annual Fall Dermatology Conference. Presented November 4, 2021.

Doug Brunk is a San Diego–based award-winning reporter for MDedge and Medscape who began covering healthcare in 1991. He is the author of two books about the University of Kentucky Wildcats men’s basketball program.

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