Measuring Psoriasis Severity at Home

Psoriatic arthritis (PsA) is an inflammatory arthritis that develops in approximately 2.9% of patients with psoriasis each year^1,2. Early prediction of which patients will develop PsA is crucial for a patient's quality of life as a diagnostic delay of as little as six months may cause irreversible damage to the joints³. A previous study had identified features associated with early-stage PsA. The three components of the Investigator's Global Assessment (IGA)-induration (thickness), erythema (redness), and desquamation (scaliness)-were highly correlated with each other and were nominally associated with subsequent PsA development. Multivariate analysis showed that a history of fingernail psoriasis and untreated induration of psoriasis lesions were independent PsA predictors⁴. Other studies have also identified psoriasis severity as associated with psoriatic arthritis^2,5,6. The collection of these clinical factors is likely to be important in future PsA screening.

Several PsA screening tests exist^7,8,9,10, but they require physicians to conduct them. A questionnaire-based screening test that can be completed by patients without physician assistance is an ideal format because it will not burden the dermatology and primary care clinics. Previously, the authors described a questionnaire with images that depict different severities of erythema and desquamation in multiple skin tones¹¹. However, the measurement of induration requires a reference card corresponding to various plaque severities, such as that developed by the National Psoriasis Foundation¹². The reference card is characterized by multiple raised areas of varying elevations, each corresponding to a number representing induration severity. To assess a patient's psoriasis severity in terms of induration, the card user compares the thickest psoriasis patch on a patient's body to the elevated areas on the card.

However, distributing a reference card to psoriasis patients may not be the most efficient approach for reaching a broad audience, especially for patients located outside the USA and for online survey studies. For researchers and clinicians gathering induration self-assessments from numerous patients, an alternative option could involve creating a homemade induration card using inexpensive office supplies. For patients, creating a homemade device from inexpensive office supplies can be more cost-effective than purchasing commercially available alternatives. This protocol describes how to create the Psoriasis Thickness Reference Card, an induration reference card that psoriasis patients can feel to assess the severity of their psoriasis induration. The Card can be made with standard office supplies and is inexpensive to make.

This study was approved by the University of Utah Institutional Review Board (IRB_00137694). Twenty-seven psoriasis patients at the University of Utah dermatology clinic were enlisted to complete a questionnaire about psoriasis severity at the time of the questionnaire's administration. All patients provided informed consent and completed the questionnaire without instructions from research or medical personnel, either before or immediately after the dermatologist's assessment.

1. Procedure for making a Psoriasis Thickness Reference Card

1. Print the Psoriasis Thickness Reference Card template (Supplemental Figure S1) on a standard piece of printer paper. If a printer is not accessible, manually write down the numbers as in the template on any paper and follow the subsequent steps.
2. Place sticky notes.
   1. Purchase a package of sticky notes. The smallest-sized sticky notes (5.08 cm height x 5.08 cm width or 5.08 cm height x 3.81 cm width) will work. The thickness of each sticky note should be between 0.09 and 0.1 mm.
      NOTE: The authors have tested multiple brands of sticky notes (see Table of Materials) in the market and found that they all fulfill this requirement. If in doubt, one can calculate the thickness of each page by dividing the total thickness of a stack of sticky notes by the number of pages in the stack.
   2. Place a stack of three sticky notes on the box labeled "3."
   3. Place a stack of 5 sticky notes on the box labeled "5."
   4. Place a stack of 8 sticky notes on the box labeled "8."
   5. Place a stack of 10 sticky notes on the box labeled "10."
   6. Place a stack of 13 sticky notes on the box labeled "13."
3. Align the adhesive side of the sticky notes on the left side of each corresponding box and press them down to adhere each stack firmly to the sheet of paper.
4. Apply a strip of tape along the right side of each stack of sticky notes (Figure 1). Ensure the tape adheres smoothly, creating a gentle slope between the top of the stack and the paper.
   NOTE: If the left side of each stack is not adhered securely to the paper via the sticky note adhesive, tape the left side in the same way as the right side.

2. Usage of the Psoriasis Thickness Reference Card

1. Slide a finger across the taped side of each stack of sticky notes to get a sense of its thickness or elevation from the paper it is adhered to.
2. In a similar manner, slide a finger across the edge of one's thickest psoriasis patch, feeling its elevation from the surrounding, unaffected skin.
3. Identify the stack that is most similar in elevation to one's thickest psoriasis patch and record the corresponding score of 0 to 13.

To validate whether patient assessments of desquamation, erythema, and induration are comparable to those of a dermatologist, 27 psoriasis patients at the University of Utah dermatology clinic were enlisted to complete a questionnaire about psoriasis severity at the time of the questionnaire's administration. Each participant was provided with a Psoriasis Thickness Reference Card along with the questionnaire. The dermatologist provided their independent assessment of the current status of each patient using the same measuring scales.

Psoriasis severity was categorized into two groups, mild versus moderate to severe. Grouping moderate and severe psoriasis aligns with the clinical management of psoriasis patients. For induration, moderate corresponds to 5-8 sticky notes and severe corresponds to 10-13 sticky notes. The accuracy of patients' assessments of desquamation, erythema, and induration was evaluated by sensitivity (the test's ability to correctly identify an individual as having the disease) and specificity (the test's ability to correctly identify an individual as not having the disease) using the physician's assessments as the gold standard. The Wilcoxon signed-rank test was used to examine whether patient assessments of psoriasis severity differed significantly from those of the attending dermatologist. Cohen's kappa was used to evaluate whether the two assessments were comparable.

The results demonstrated that the patients' and physician's answers to some questions regarding psoriasis severity are moderately to highly concordant (Figure 2 and Table 1). The numbers of physician-patient severity assessments with matching values were 23 (85.2%), 25 (92.6%), and 22 (84.6%) for desquamation, erythema, and induration (which was answered by 26 out of 27 participants), respectively. There was no significant difference between patient and physician reports of desquamation (p = 0.42), erythema (p > 0.99), and induration (p > 0.99) by the Wilcoxon signed-rank test. Sensitivity ranged from 0.83 to 0.93 and specificity from 0.77 to 0.92. Cohen's kappa values revealed at least some level of agreement between the physician and patient assessments of all three variables (kappa scores > 0.69, p-values < 0.000002). Using Cohen's kappa interpretations suggested by McHugh¹³, moderate agreement was observed between physician and patient measurements of desquamation and induration; physician and patient measurements of erythema exhibited strong agreement.

Figure 1: Completed Psoriasis Thickness Reference Card. The number under each square in the card indicates the number of sticky notes in each stack. The stacks of sticky notes are attached to the paper using the adhesive side of the notes on the left and a piece of tape on the right. Please click here to view a larger version of this figure.

Figure 2: Proportions of patient assessments that matched or did not match physician assessments. Each patient rated the severity of their current psoriasis lesions based on three psoriatic features; the attending dermatologist also rated each patient's psoriasis severity on the same scale. Each of the three columns represents physician ratings; the width of each column represents the proportion of patients given that rating by the physician. Within each column, the different colors represent the proportion of those patients given a specific physician rating who were also given a specific patient rating, e.g. approximately 50% of the patients who were assessed as having severe erythema by a physician were self-assessed as having moderate erythema. (A) Desquamation, (B) erythema, and (C) induration. Abbreviation: NA = not applicable (patient did not provide an assessment). Please click here to view a larger version of this figure.

Table 1: Predictive value, sensitivity, and specificity of patient psoriasis severity ratings. Physician ratings were treated as the true values to which the patient ratings were compared. *Positive is moderate to severe psoriasis; negative is mild to no psoriasis. Abbreviation: CI = confidence interval.

Supplemental Figure S1: Psoriasis thickness Reference Card template. The template may be printed and used to directly place the sticky notes on, or it may be used as a guide for numbering and placing sticky notes on a sheet of paper if no printer is available. Please click here to download this File.

Protocol step 1.4 is a crucial aspect of the proper construction of the Psoriasis Thickness Reference Card. To achieve an accurate representation of plaque thickness, it is imperative to avoid placing the tape vertically or flush against the vertical edge of the stack of sticky notes. If the tape is positioned in such a manner, the sharp edge of each stack will not mimic the feel of a psoriasis plaque. The tape should be applied in a way that creates a smooth slope connecting the stack to the paper.

Since the method is relatively simple, there are limited instances where modifications and troubleshooting might be necessary. If the sheet of printer paper is too flimsy, a piece of cardstock can be used as an alternative. Furthermore, in case the left sides of the stacks of sticky notes lose their adhesiveness, the left side of each stack may be taped to the paper using the same instructions as described in protocol step 1.4.

The main alternative method for induration scoring involves the physician assessing the patients' induration severity. While this approach benefits from the expertise of a trained professional, it does require additional time during the visit, and it may not be practical for patients in remote locations. To address these challenges, the Psoriasis Thickness Reference Card offers a solution by empowering patients to conduct the induration assessment themselves before their clinic visit or even from the comfort of their home. This patient-driven approach provides a convenient and efficient means of monitoring induration severity. Moreover, research indicates that induration severity at its worst holds a greater predictive value for PsA than induration severity at the time of a clinical visit⁴. Therefore, frequent monitoring of psoriasis thickness by patients is more likely to yield data that are relevant for PsA prediction, enhancing the accuracy of the assessment and potentially leading to early detection and intervention.

Patients can utilize the card to assess the severity of induration in their psoriasis lesions, but it demonstrates only moderate concordance with the doctor's assessment. The cause of the discordance between patient and doctor assessments is not entirely clear.

A 2022 study found that a Patient-oriented Psoriasis Area and Severity Index had good interrater reliability and was positively correlated with the Psoriasis Area and Severity Index (PASI) as calculated by physicians. The present study did not include the percentage of body surface affected (BSA) and PASI. While BSA has been shown to be associated with PsA^5,14, previous research demonstrates that induration is a stronger predictor⁴. Furthermore, both BSA and PASI are more challenging to measure, making them less suitable for patient self-assessment. As a result, BSA and PASI were not incorporated into the study.

In conclusion, the use of the Psoriasis Thickness Reference Card empowers psoriasis patients to independently measure the thickness of their psoriasis lesions. This approach can be utilized in a screening test to predict PsA development in individuals with cutaneous-only psoriasis. Advantages include simplicity, cost-effectiveness, and self-reliance, enabling convenient administration even for patients situated in remote locations. This approach has the potential to expand PsA risk assessment accessibility and reduce research costs related to psoriasis and PsA.