Disease Burden and Quality of Life in Psoriasis Patients With and Without Comorbid Psoriatic Arthritis: Results From National Psoriasis Foundation Panel Surveys

Approximately 3% of the US adult population, or roughly 5 million Americans, have been diagnosed with psoriasis.¹ Psoriasis has a high disease burden, with one review of 817 quality-of-life (QOL) studies concluding that the degree to which psoriasis negatively affects patients’ QOL is comparable with major diseases such as diabetes mellitus or cancer.²

Psoriatic arthritis (PsA) is a chronic, often progressive, inflammatory arthropathy that can lead to permanent joint damage and severe disability.^3,4 Psoriatic arthritis is a common comorbidity among patients with psoriasis, affecting 6% to 10% of psoriasis patients overall⁵ and 20% to 40% of psoriasis patients with more extensive skin involvement.^5-7

The comorbidity profile and overall disease impact are not well understood in psoriasis patients with and without comorbid PsA. The primary objective of this study was to compare disease characteristics, comorbidities, and psoriasis-related QOL in patients with moderate to severe psoriasis with and without comorbid PsA.

Methods

Study Design and Participants

Since 2003 the National Psoriasis Foundation (NPF) has conducted semiannual survey panels to collect patient-reported data on topics including disease characteristics, treatment utilization, and psoriasis-related QOL impact. Responses from approximately 5604 individuals have been collected and analyzed from a total of 13 survey panels conducted from 2003-2009 and 2011. No data were available for 2010. In each survey panel, responses from approximately 400 randomly selected respondents were collected, with approximately 300 respondents having moderate to severe psoriasis and 200 respondents being NPF members. Respondents were surveyed via telephone and the Internet.

This study examined 2 main patient groups: (1) adults (>18 years of age) with psoriasis alone and (2) those with comorbid PsA. The 2 study groups were subdivided according to percentage of body surface area (BSA) affected; specifically, patients with psoriasis alone were classified as having mild psoriasis (<3% BSA) or moderate to severe psoriasis (>3% BSA) and patients with PsA were classified as having mild to no psoriasis (<3% BSA) or moderate to severe psoriasis (≥3% BSA).⁸

Assessments

Comparisons of patient demographics, disease characteristics, comorbidities, psoriasis-related QOL, and symptom impact were made for patients with moderate to severe psoriasis and PsA versus those with moderate to severe psoriasis alone. The overall impact of psoriasis on patients’ physical and emotional QOL was assessed via a 12-item survey with each item rated on an 11-point scale (0=not at all; 5=somewhat; 10=very much). Total QOL scores ranged from 0 to 120. Higher scores indicated greater (ie, worse) impact of psoriasis on the patient’s QOL. To evaluate symptom impact (ie, to what degree a patient felt affected by individual symptoms), ratings from 3 symptoms—itching, irritation, and pain—that were included in the overall QOL assessment also were analyzed individually. Results also were compared for patients with mild psoriasis alone versus those with moderate to severe psoriasis alone as well as for patients with PsA and mild to no psoriasis versus those with PsA and moderate to severe psoriasis.

Statistical Analysis

Adult survey respondents who answered survey questions relevant to the analysis were included. For patient demographics and comorbidities, t tests were used for continuous variables and Χ² tests were used for categorical variables. For overall psoriasis-related QOL and symptom impact scores, differences among the study groups were compared using analyses of covariance, which adjusted for age, gender, and race. All analyses were conducted using SAS version 9.2.

Results

Patient Demographics

Of 5467 total respondents, 3532 reported moderate to severe psoriasis of which 1280 (36.2%) had comorbid PsA (Table 1). Compared to patients with moderate to severe psoriasis alone, those with moderate to severe psoriasis and comorbid PsA were older, less commonly male, less likely to be employed, had a longer duration of psoriasis, were more likely to be white, and were more likely to have health insurance coverage. Among the psoriasis alone group, those patients reporting moderate to severe psoriasis were younger, less likely to have health insurance coverage, and were less likely to be treated by a dermatologist only than those with mild psoriasis. Among the group with PsA, patients with moderate to severe psoriasis were more likely to be treated by a dermatologist only versus those with mild or no psoriasis (Table 1).