Age of psoriasis onset decides if the skin or joints act up first

By Dr. Liji Thomas, MDNov 11 2019

People with psoriatic arthritis may initially present with either psoriasis or arthritis as the first symptom/sign of this illness. Now, a new study presented at the 2019 ACR/ARP Annual Meeting shows that the age at which psoriasis develops is a key predictor of which shows up first. Early-onset psoriasis is not strongly associated with arthritis while late-onset psoriasis is.

The finding may indicate that PsA patients who first present with skin lesions could actually be a different subgroup of this disease, and perhaps associated with poorer responses to treatment.

The researchers also say that pustular psoriasis advances arthritis onset by 2 years, while the additional involvement of the nails or appearance of plaques, or having a family member with psoriasis, is associated with a delay of 2 years each, before arthritis sets in.

The interrelationships between characteristics of skin psoriasis, arthritis and the timing of arthritis are not well studied; the research sought to explore these in a large international cohort. Image Credit: KochaTango / Shutterstock

Psoriatic arthritis

Psoriatic arthritis (PsA) refers to a chronic type of joint inflammatory condition that is typically found in people with psoriasis. Psoriasis is a condition that appears as peeling of skin in large patches with red, inflamed areas underneath, due to a genetic abnormality in the rate at which skin cells push themselves to the surface from the deeper layers where they originate. In normal skin, the skin cells take several days to mature, and migrate from deep to superficial slowly, so that the topmost layer is composed of dead skin cells. In psoriasis, things are otherwise.

PsA can occur in people without psoriasis, especially if there is a history of the skin condition in the family. However, PsA has a wide variety of manifestations, affecting different joints in different people, and progressing at different rates and in different patterns. The appearance of skin lesions is also very variable. And of course, the question of whether the psoriasis or the arthritis appears first is very unsettling.

The study

The current study aimed to answer this question – which comes first, and how is it related to the time of disease onset? The researchers took data from the PsART-International web registry of patients with PsA who are being treated in Turkey, Italy and Canada. They were thus able to delve into the details of patient history, including the type and age of onset of skin and joint manifestations. However, all patients in this group first presented with initial arthritis symptoms, before any skin lesions appeared. Thus they represent about 5-10% of all patients with PsA, who are more likely to have arthritic symptoms later in the course of the disease.

The importance of knowing how the age of onset is different in each case could help predict the course, according to the researchers, because it could indicate two different subgroups of the same clinical condition. Despite the association of psoriasis and arthritis, the illnesses could be actually quite different in their causes. This could mean they need to be treated differently and may have different outcomes as well.

The researchers obtained data on over 1,600 patients. They looked at the demographic background, looked for a family history of psoriasis or PsA, the type of skin lesion demarcating different types of psoriasis, the site of onset of skin lesions, and the first PsA manifestation to be observed. Using these details, they classified the patients in three groups.

Group 1 included those with arthritis as the initial manifestation, group 2 those with psoriasis first, and group 3 those in whom the two occurred within 12 months of each other, or synchronously. Among them, 71 were group 1, while group 2 and 3 had 309 and over 1,250 patients respectively.

Their analyzed the data to find out how much time, in months, passed before patients developed arthritis, and vice versa. The time, called the model intercept, was represented as positive and negative numbers, depending on whether the psoriasis or the arthritis occurred first, respectively.

The findings

The technique, called cluster analysis, shows that there are six different variables related to psoriasis that affect the relationship between arthritis and psoriasis. These are the age of onset of the disease, the extent of skin lesion distribution, the presence of pustular or plaque psoriasis, the involvement of nails, and the involvement of the musculoskeletal system.

The study shows that the age at which psoriasis first occurs determines whether the patient presents with arthritis or psoriasis first. Moreover, when psoriasis is the first to manifest, there is a delay of 65 months before arthritis sets in, after adjusting for other confounding variables.

When pustular psoriasis was present, arthritis occurred about 2 years earlier than predicted by the model intercept. The other factors caused a delay of 2 years each from the model intercept before arthritis sets in.

In particular, the age of onset was picked out as especially important because of its relationship with the genetic predisposition to the disease. In cases where the disease sets in early, the HLA-Cw6 gene is predominantly found, but not in late-onset cases.

Implications

The current study found that arthritis was highly dependent on psoriasis of late onset, suggesting a different origin for this condition, as well as a poorer prognosis for this subgroup.

Researcher Umut Kalyoncu says, “We need more patients to determine related factors. If patients with arthritis first are really a different subgroup, it means that treatment response and prognosis could be different from others. Indeed, in our cohort, achieving minimal disease activity is statistically less frequent in patients with arthritis first. If these results are confirmed in other, well-defined PsA cohorts, we may have determined a subgroup of this highly heterogeneous disease.”