Psoriatic Arthritis for the Dermatologist

In his Fall Dermatology Week 2022 session, “Psoriatic Arthritis for the Dermatologist,” Joseph F. Merola, MD, MMSc, discussed the shared pathogenesis of psoriasis (PsO) and psoriatic arthritis (PsA), the disease domains and clinical manifestations of PsA, how to conduct screening for PsA in patients with PsO, and how to formulate a treatment plan that considers disease domains and comorbidities.

Dr Merola began with an overview of the shared pathogenesis concept, “There is certainly some shared overlap of genetic risk, although there are distinct elements of PsO and PsA. There are some potentially shared environmental triggers. Ultimately, what you see are a lot of the same players, such as IL-23, IL-17, and TNF. The same innate and adaptive immune cellular players that we would expect in the skin are ultimately causing the pathogenesis in the joints.”

He then presented clinical considerations by noting that about one-third of patients with PsO go on to develop PsA, and 75% to 85% percent of patients have PsO before PsA. “As dermatologists, we need to understand that we are the providers who are seeing the at-risk population who will develop PsA and it is on us to screen and ask patients about PsA symptoms so we can either manage it or comanage it with the rheumatologist,” Dr Merola remarked. He added, “There has been at least 1 study that suggests an annual rate of conversion of about 3% per year.”

Dr Merola shared challenges for dermatologists in PsA management, such as the heterogeneity of disease; lack of a diagnostic test; limited awareness of PsA among nonrheumatologists; and treatment complications, such as limited ability to predict the response to the mechanism, variable response by disease domain, and numerous potential comorbidities to consider.

To unpack this further, he explained that PsA is characterized by diverse clinical features within 6 disease domains:

• Peripheral arthritis
• Axial disease
• Enthesitis
• Dactylitis
• Skin involvement
• Nail involvement

“A delay in diagnosis as brief as 6 months is associated with increased risk of damage, functional disability, and joint deformity,” he stressed. PsA can be a deforming arthritis in about half of patients.

Regarding differential diagnoses, Dr Merola highlighted:

• Osteoarthritis
• Rheumatoid arthritis
• Crystal athropathy
• Lyme arthritis

He also provided tips for distinguishing inflammatory from noninflammatory arthritis. With inflammatory arthritis, patients will have stiffness after a period of inactivity that improves with activity; redness, warmth, and swelling; systemic symptoms; a response to anti-inflammatory medication; and a family history. Whereas patients with noninflammatory arthritis are more likely to experience no significant period of stiffness after inactivity, stiffness that worsens with activity or at the end of the day, and specific joint patterns.

When screening for PsA, Dr Merola suggested using the mnemonic PSA, “Ask patients about joint pain, following up with a question about stiffness. Swelling and sausage digit are another 1 or 2 Ss. And then A for axial disease. Ask about back pain, especially in younger patients. If we have 2 out of 3 of these present, we should think about more formal screening or referral.”

There are several validated screening tools that can be used in the clinic, such as the 5-question Psoriatic Epidemiology Screening Tool, which is one of the easiest to use, according to Dr Merola. PsA is largely a clinical diagnosis, but tests may include ESR, CRP, RF/anti-CCP, and imaging such as X-rays and MRI.

Radiographic characteristics of PsA include:

• Joint erosion
• Joint space narrowing
• Periarticular and shaft periostitis
• “Pencil-in-cup” deformity
• Acro-osteolysis
• Ankylosis
• Spur formation
• Spondylitis

Dr Merola finished by discussing the complete treatment of PsA, “For PsA patients with PsO, optimal improvement in health-related quality of life as measured by select domains of patient-reported outcomes was dependent on successful treatment of both joint and skin symptoms.” He added that “comorbidities make the management of PsA challenging but also meaningful for patients when we can align our therapies to address multiple comorbid conditions.”

He concluded, “As dermatologists, we have to own getting the patient connected with an appropriate clinical team. One of the ways we think about that is by fostering combined clinic models and local/regional partnerships among dermatologists, rheumatologists, and other specialists.”

Reference

Merola JF. Psoriatic arthritis for the dermatologist. Presented at: Dermatology Week 2022; September 14-17, 2022; Virtual.