What the Severity of Skin Symptoms Says About Joint Health in Psoriatic Arthritis

While skin and joint symptoms share some underlying causes in psoriatic arthritis, there’s no exact correlation between the two. But there may be patterns in psoriasis symptoms that predict who will develop psoriatic arthritis, or help predict disease activity once someone develops psoriatic arthritis.

Here’s what you should know about the link between skin and joint symptoms in psoriatic arthritis.

Historically, it was widely understood that in some people with psoriasis, psoriatic arthritis would develop later on — typically years after skin symptoms appeared. But research has shown that the relationship between skin and joint symptoms may be more complicated in some people.

“There are people who get both at the same time,” says Eric Ruderman, MD, a rheumatologist at Northwestern Medicine in Chicago. “And there are people who get joint symptoms first, that look like psoriatic arthritis, but they don’t have psoriasis. Yet a few years later they develop a patch of psoriasis, or they have a strong family history of psoriasis.”

“Psoriasis and psoriatic arthritis are increasingly understood as manifestations of a single overarching ‘psoriatic disease’ continuum,” says Rebecca Gordon, MD, a rheumatologist at UCHealth Cherry Creek Medical Center in Denver. Dr. Gordon notes that both conditions share the same set of immune system pathways, with an established biological “bridge” between skin and joint disease activity.

There are several different ways to quantify, or measure, the severity of skin disease in psoriasis and psoriatic arthritis.

• Body Surface Area (BSA) This is a marker of how much of your body is covered by active psoriasis, with an area the size of your handprint equal to roughly 1 percent.

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• Psoriasis Area and Severity Index (PASI) This tool uses both the size and severity of psoriasis lesions to create a score for each of four body regions: head and neck, upper limbs, trunk, and lower limbs.

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• Physician Global Assessment (PGA) In this rating system, doctors visually score psoriasis severity in different areas of the body.

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• Special Site Involvement Your doctor may note psoriasis in certain areas of your body, such as your scalp, face, hands, feet, nails, genitals, or skin folds. Disease in these areas is linked to worse quality of life.

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When assessing psoriasis severity, “Patient impact such as itching, sleep issues, embarrassment, or clothing choices are also taken into account,” says M. Elaine Husni, MD, MPH, a rheumatologist and the director of the Arthritis and Musculoskeletal Center at Cleveland Clinic in Ohio.

There are a few ways to measure how joints are affected in psoriatic arthritis.

• Tender/Swollen Joint Count (SJC66/TJC68) This assessment looks at swelling in 66 joints and tenderness in 68 joints throughout the body.

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• Patient Global Assessment (PtGA) This tool uses a patient’s self-reported pain and other signs of disease activity to create a score.

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• Disease Activity in Psoriatic Arthritis (DAPSA) This scoring system combines tender/swollen joint count, patient-reported pain scores, and a key measure of inflammation in the body.

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• Imaging Results Your doctor may evaluate joint damage and look for signs of inflammation, such as in the area where tendons and ligaments connect to bones (enthesitis).

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Gordon notes that there are also specialized assessments for scoring the severity of enthesitis, dactylitis (“sausage fingers” or toes), and spinal disease in psoriatic arthritis. “Oftentimes, a complete musculoskeletal and skin exam will incorporate these measures even if not formally identified as such,” she says.

A few studies have given insights into the connection between skin symptoms and joint health in psoriatic arthritis. But it’s important to note that overall trends won’t necessarily apply to an individual.

“Skin and joint disease are connected, but they do not always track together,” says Dr. Husni. “A patient may have severe psoriasis with mild arthritis, or minimal skin disease with aggressive joint inflammation.”

Practically speaking, there are a couple of key lessons from the relationship between skin and joint involvement in psoriatic arthritis — the importance of detection of psoriatic arthritis if you have psoriasis, and the importance of taking skin symptoms into account when deciding on treatment.

“Skin symptoms can strongly influence treatment choice,” says Husni. “Severe psoriasis, nail disease, or difficult sites such as the scalp, palms, soles, or genitals may favor therapies with strong skin efficacy” that also target joint inflammation.

Dr. Ruderman says that when choosing a biologic drug, in many cases, “If you’re trying to get control of the skin, you pick the drug that’s going to best control the skin without so much worrying about what’s going to happen in the joints. Because most of them will work pretty well in the joints.” But in some cases, he says, a drug can adequately control skin disease but not joint disease. “So then you might have to switch over and try a different biologic.”

Above all, Ruderman says, it’s important to make sure all aspects of a person’s psoriatic arthritis are accounted for in treatment decisions. “It really does become a conversation with the rheumatologist, the dermatologist, and the patient to try to find the best targeted treatment that’s going to manage all of the symptoms that bother them,” he says.

• Most people with psoriatic arthritis also have psoriasis and skin involvement, and some of the same biological pathways explain both skin and joint disease.
• More severe skin disease in psoriatic arthritis is linked to worse overall disease and worse quality of life.
• It’s important to follow a treatment strategy that takes all aspects of your disease into account, including skin involvement. Many available therapies target both skin and joint disease, but may not work well in both areas for all people.