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Year : 2020  |  Volume : 11  |  Issue : 2  |  Page : 50-54

Interobserver variation of psoriasis area and severity index in a clinical setting

Department of Dermatology, Father Muller Medical College, Mangalore, Karnataka, India

Date of Submission01-Jan-2020
Date of Acceptance15-Dec-2020
Date of Web Publication25-May-2021

Correspondence Address:
Dr. B Nanda Kishore
Department of Dermatology, Father Muller Medical College, Mangalore - 575 002, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjmsr.mjmsr_1_20

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Background: Severity scoring systems are important parameters in assessing the severity of a disease aiding in categorization of disease and its prompt treatment. However, reliability of these scoring systems and inter-observer variation is a concern. In the recent years, there has been a lot of debate on reliability of Psoriasis Area and Severity Index (PASI) scoring as there is a wide range of difference in the scoring when assessed by each observer. We conducted this study to assess the inter-observer variation of PASI scoring observed in out-patient department of Dermatology at a tertiary care hospital. Methods: Total of 35 patients clinically presenting with chronic plaque type psoriasis, irrespective of disease duration and treatment taken were enrolled in the study. PASI scoring was assessed by 3 different observers (2st year, 3nd year postgraduate residents and clinical staff) independently on each patient and reliability was determined by intra-class coefficient. (ICC). Results: Our study showed an excellent reproducibility of PASI score when an inter-observer variation was performed. Most of the parameters showed an agreement of >0.9 (ICC) which was statistically significant (<0.001). However it was noted that “erythema” in head, upper limbs and lower limbs was in less agreement with ICC when compared to other parameters, yet excellent. Mean PASI score was 10.96, 10.78 and 10.47 among observer 1, 2 and 3 respectively. Conclusion: Our study concludes that PASI is a reproducible and reliable clinical tool with less inter-observer variation if done by trained qualified observers to assess the severity of chronic plaque type psoriasis although its application gets tedious and difficult in busy dermatology clinics. Limitation: A small sample size.

Keywords: Inter-observer variation, ICC, inter-rater reliability, PASI score, reliability, psoriasis area and severity index, psoriasis severity

How to cite this article:
Dias NS, Kishore B N, Sukumar D. Interobserver variation of psoriasis area and severity index in a clinical setting. Muller J Med Sci Res 2020;11:50-4

How to cite this URL:
Dias NS, Kishore B N, Sukumar D. Interobserver variation of psoriasis area and severity index in a clinical setting. Muller J Med Sci Res [serial online] 2020 [cited 2021 Aug 5];11:50-4. Available from: https://www.mjmsr.net/text.asp?2020/11/2/50/316687

  Introduction Top

Psoriasis area and severity index (PASI) is the most widely used tool in the assessment of severity of chronic plaque-type psoriasis in a clinic for choosing a suitable treatment modality and it is very helpful in clinical trials of newer drugs to assess the treatment response.[1],[2],[3] In 1978, Fredriksson and Petersson first developed it to assess the treatment efficacy of a new retinoid drug in a clinical trial.[2]

PASI scoring helps to evaluate the severity of psoriasis by considering three parameters in morphology of a lesion which includes erythema (redness), scaling (desquamation), and induration (thickness) which is observed in four different anatomic sites of the body (head, upper limbs, trunk, and lower limbs) taking the area of involvement into consideration. These scores are combined to generate a score which determines severity which can be between 0 and 72, most cases falling between 0 and 15. It becomes important to know whether a particular drug is effective or not by considering the severity of disease that comes down following treatment, mainly in clinical trials.[2]

Although PASI is a gold standard tool for psoriasis, its reliability is criticized as it is nonlinear, complex, and lengthy, making it more tedious to be used in clinics. It is also observed that scoring varies when observed by different observers and also intraobserver variations are noted when time-to-time assessments are done, making its reliability a question. Further, PASI is a complex equation without any automated calculating tool which gives a calculating error. This implies the need for expertise training for all clinicians and its use needs to be employed more frequently to get a better understanding and reduce inaccurate recordings.[3] Current guidelines tend to categorize psoriasis patients according to PASI, with moderate-to-severe patients having scores between 10 and 12.[4]

PASI score was considered more superior than the physician's global assessment (PGA) and equally good as the Copenhagen Psoriasis Severity Index in earlier studies.[5] Few other studies showed that the Lattice system PSA to be a better modality than PASI.[6] When various scoring systems are studied together for psoriasis, it is observed that none of them gave excellent concordance with reliability deeming it ideal in assessment; however, PASI score was most extensively studied.[7]

This study is conducted to evaluate the reliability of scoring system when observed by three different observers of different years of experience in practice to highlight the role of knowledge and experience in its assessment which deems a proper training to budding clinicians.

  Materials and Methods Top

This is an observational prospective type of study enrolling a minimum of 35 patients of chronic plaque-type psoriasis conducted at the Outpatient Department of Dermatology, Venereology, and Leprosy of Father Muller Medical College Hospital, Kankanady, Mangalore, from October 2017 to March 2018.

Patients of chronic plaque psoriasis irrespective of age, gender, chronicity, and severity are enrolled in the study. Three different observers (including postgraduate residents and clinicians) evaluate the same patients and determine the PASI score for each patient separately.

Four sites of affection, the head (h), upperlimb (u), trunk (t), and lower limbs (l), are separately scored using three parameters, erythema, induration, and desquamation, each of which is graded on a severity scale of 0–4, where 0 = nil, 1 = mild, 2 = moderate, 3 = severe, and 4 = very severe. The area-wise percentage involvement of the involved sites is calculated as: 1 = less than 10% area; 2 = 10%–29%; 3 = 30%–49%; 4 = 50%–69%; 5 = 70%–89%; and 6 = more than 90%.

The final formula for the PASI score is:

PASI = 0.1 (Eh + Ih + Dh) Ah + 0.2 (Eu + Iu + Du) Au + 0.3 (Et + It + Dt) At + 0.4 (El + Il + Dl) Al

The PASI score varies from 0 to 72.

The interobserver variation of PASI is evaluated based on intraclass correlation coefficient (ICC), which allowed the assessment of consistency and reproducibility of the measurements.

Statistical analysis

Data were analyzed for statistical significance to assess interobserver reliability and consistency using mean, standard deviation, and intraclass coefficient (ICC).

  Results Top

The results are based on assessment done by three observers with 5, 3, and 2 years of experience. [Table 1] shows mean and standard deviation of each parameter of PASI score at different anatomical locations as observed by three observers. The mean scores of observers 1, 2, and 3 were 10.96, 10.78, and 10.47, respectively, which shows an excellent concordance as depicted in [Figure 1]. PASI scoring of 35 subjects assessed by three different observers is depicted in [Table 2], showing that higher PASI scores showed more discrepancy. [Figure 2] shows PASI values among three observers in a scatter plot which shows that observations for each subject by three observers are close to each other, almost replicating each other.
Table 1: Mean and standard deviation of psoriasis area and severity index scores in three different observers

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Figure 1: Psoriasis area and severity index score mean values among three observers

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Table 2: Intraclass correlation coefficient of psoriasis area and severity index scoring

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Figure 2: Scatter plot chart for psoriasis area and severity index scoring for three observers among 35 patients

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Analysis for interobserver variation was done using ICC, which assessed if there was significant agreement among three different observers. [Table 3] depicts the ICC at a confident interval of 95% with its respective significance level (P value). If the ICC value is close to 1, it represents stronger agreement and if closer to 0, it represents a poor agreement among the observers.
Table 3: Psoriasis area and severity index scores of 35 patients as observed by three different observers

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ICC <0.20 – no agreement

ICC = 0.2–0.4 – weak agreement

ICC = 0.4–0.6 – moderate agreement

ICC = 0.6–0.8 – good agreement

ICC >0.8 – excellent agreement

In our study, ICC was 0.963 at 95% CI, showing an excellent agreement. Erythema shows a lower ICC in the head, upper limb, and lower limb (<0.9) yet an excellent agreement.

  Discussion Top

Interobserver variability shows the strength of agreement among various observers on the same subjects applying the same tool for assessment. Intrarater reliability is the degree of agreement with multiple repetitions of test performed by a single observer. Our study showed an excellent degree of agreement among the observers proving that the PASI score is a reliable tool to assess the severity of psoriasis. However, for “erythema,” the agreement was comparatively low, suggesting that erythema is difficult to quantify and this can be a parameter in the scoring which may lead to a discrepancy in results.

Patients with higher PASI scoring showed more variability in scoring indicating that reliability of PASI scoring decreases with the severity of the disease.

PASI score lacks various parameters such as nail changes, arthropathy, and symptoms associated with the scoring which may add to the severity of disease and may aid in proper suitable therapy.

Even though PASI is proven reliable in various studies, it depends on the quality of assessment done by observers hampering the treatment choice and clinical trials; hence, a proper training is required for the postgraduates and more frequent usage improves its quality in assessment.

We feel that there is a need of a simpler diagnostic tool to assess the severity of psoriasis, as it can minimize calculating errors and helps in assessing patients in busy clinics and is also reliable at the same time.

  Conclusion Top

Our study concludes that PASI scoring is an excellent tool to assess the severity of psoriasis with less interobserver variation provided the observers are well trained in its assessment, although it is tedious to employ it without a calculator in a busy dermatology clinic. The limitation of our study included the low sample size.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Cabrera S, Chinniah N, Lock N, Cains GD, Woods J. Inter-observer reliability of the PASI in a clinical setting. Australas J Dermatol 2015;56:100-2.  Back to cited text no. 1
Faria JR, Aarao AR, Jimenez LM, Silva OH, Avelleira JC. Inter-rater concordance study of the PASI. An Bras Dermatol 2010;85:625-9.  Back to cited text no. 2
Youn SW, Choi CW, Kim BR, Chae JB. Reduction of inter-rater and intra-rater variability in psoriasis area and severity index assessment by photographic training. Ann Dermatol 2015;27:557-62.  Back to cited text no. 3
Gourrand PA, Le Gall C, Puzenat E, Aubin F, Ortonne JP, Paul CF. Why statistics matter: Limited inter-rater agreement prevents using the psoriasis area and severity index as a unique determinant of therapeutic decision in psoriasis. J Invest Dermatol 2012;132:2171-5.  Back to cited text no. 4
Berth Jones J, Thompson J, Papp K. A study examining inter-rater and intra-rater reliability of a novel instrument for assessment of psoriasis. Br J Dermatol 2008;159:407-12.  Back to cited text no. 5
Puzenat E, Bronsard V, Prey S, Gourraud PA, Aractingi S, Baqot M. What are the best outcome measures for assessing plaque psoriasis severity? A systematic review of the literature. J Eur Acad Dermatol Venereol 2010;24:10-6.  Back to cited text no. 6
Langley RG, Ellis CN. Evaluating psoriasis with psoriasis area and severity index, psoriasis global assessment and lattice system physician's global assessment. J Am Acad Dermatol 2004;51:563-9.  Back to cited text no. 7


  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3]


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