Reliability of the Ichthyosis Scoring System in Individuals With Skin of Color

This cross-sectional study assesses the reliability of the Ichthyosis Scoring System in individuals with Fitzpatrick IV to VI skin types.

Key Points

Question

Is the Ichthyosis Scoring System reliable in individuals with skin of color (ie, Fitzpatrick IV-VI skin types)?

Findings

In this cross-sectional study of 94 photographs of ichthyosis among 61 individuals, the Ichthyosis Scoring System demonstrated equal individual body site reliability when scoring scale and erythema for all phototypes.

Meaning

This study suggests that the Ichthyosis Scoring System can confidently be applied to skin of all phototypes to assess ichthyosis severity at relevant body sites in clinical and research settings to direct therapeutic decision-making, monitor treatment efficacy, and guide enrollment in clinical trials.

Abstract

Importance

The Ichthyosis Scoring System (ISS) is a reliable instrument for assessing ichthyosis severity. The ISS’s performance in individuals with skin of color (ie, Fitzpatrick IV-VI skin types) remains unknown because it was initially assessed in individuals with Fitzpatrick I to III skin types.

Objective

To assess the reliability of the ISS in individuals with Fitzpatrick IV to VI skin types.

Design, Setting, and Participants

In this cross-sectional study, 14 dermatologists used the ISS to rate 94 test photographs, 47 from individuals with Fitzpatrick I to III skin types and 47 from individuals with Fitzpatrick IV to VI skin types. The professional photographs were obtained from the National Registry for Ichthyosis and Related Disorders, which enrolls participants with ichthyosis from referral centers, patient advocacy groups, and self-referral worldwide. Test photographs represented individuals of all phototypes with ichthyosis of all severities. Due to limited comprehensive, high-quality photography among individuals with Fitzpatrick IV to VI skin types, 4 body sites were chosen: upper back, legs, upper arm, and dorsal feet. From August to December 2023, dermatologists independently scored the same test photographs and were blinded to photographic groupings. Data were analyzed in March 2024.

Main Outcomes and Measures

Interrater reliabilities were determined using interrater intraclass correlation coefficients (ICCs) using the two-way random effects model.

Results

Of the 61 individuals with ichthyosis represented in the 94 photographs, 28 (46%) were younger than 18 years and 33 (54%) were 18 years and older; 32 (52%) were female and 29 (48%) were male; and 1 (2%) was American Indian, 16 (26%) were Black, 6 (10%) were Hispanic, 1 (2%) was Pacific Islander, 5 (8%) were South Asian, 31 (51%) were White, and 1 (2%) was White and Hispanic. For individuals with Fitzpatrick I to III skin types, scale and erythema ICCs ranged from 0.97 (95% CI, 0.93-0.99) to 0.99 (95% CI, 0.98-1.00) and 0.91 (95% CI, 0.79-0.97) to 0.95 (95% CI, 0.89-0.99), respectively. For individuals with Fitzpatrick IV to VI skin types, scale and erythema ICCs ranged from 0.97 (95% CI, 0.93-0.99) to 0.99 (95% CI, 0.98-1.00) and 0.90 (95% CI, 0.80-0.96) to 0.94 (95% CI, 0.86-0.98), respectively. The overlap of ICC confidence intervals demonstrates ISS reliability across phototypes.

Conclusions and Relevance

This cross-sectional study shows that the ISS can be applied across phototypes to measure ichthyosis severity. Further studies using full-body photographs would further bolster the ISS’s reliability to assess global ichthyosis severity. These findings set the stage for increasing diversity in ichthyosis clinical trials.

Introduction

Ichthyoses are heritable epidermal differentiation disorders characterized by varying degrees of scaling and erythema.¹ Quantifying erythema and scaling severity is crucial for guiding treatment, monitoring efficacy, and clinical trial enrollment.² The Ichthyosis Scoring System (ISS) has proven to be a reliable instrument in assessing ichthyosis severity in person and with photographic evaluation.^3,4 However, the ISS’s applicability to skin of color (ie, Fitzpatrick IV-VI skin types) remains unclear, as initial validations included predominantly individuals with Fitzpatrick I to III skin types.^3,4 Because erythema evaluation in skin of color can be challenging due to increased baseline pigmentation,⁵ we assessed the ISS’s reliability in such phototypes.

Methods

Study Design

In 2023, 94 professional photographs from 61 individuals representing the full spectrum of severity were selected from the National Registry for Ichthyosis and Related Disorders dataset (Figure 1). A.J.L and K.A.C reviewed the 117 available photographs of individuals with Fitzpatrick IV to VI skin types, showcasing the upper back, upper arm, legs, and dorsal feet—sites selected for clarity and abundance. Of these, 47 high-quality photographs were chosen based on their print clarity, representation of the full severity range of scale and erythema, and even body site distribution. An additional 47 photographs of individuals with Fitzpatrick I to III skin types were then selected to match the Fitzpatrick IV to VI skin type group in both scale and erythema severity.

Figure 1. Example Test Photographs From Individuals With Fitzpatrick I to III and IV to VI Skin Types.

The ISS uses 5-point Likert scales to separately score scale and erythema severity. Severity levels are represented by photographic and written standard descriptions. Compared to prior tools, the ISS photographic standards use a greater proportion of images from individuals with skin of color (42.2%).³ Scale was assessed using ISS torso standards representing the full severity spectrum. Erythema was assessed using a single standard set representing all severity levels in Fitzpatrick I to III skin types.

ISS validation was performed by 14 board-certified dermatologists who independently scored 94 test photographs for scale and erythema. Dermatologists participated in an ISS training session and were provided with physical copies of test photographs and photographic and written standards. Test photographs were randomly ordered to reduce order bias.

This study was approved by the institutional review board at Yale University. Written informed consent and assent were obtained from participants 7 years and older and from parents of minors. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines.

Participants

Age, sex, and race and ethnicity (American Indian, Black, Hispanic, Pacific Islander, South Asian, and White) were self-reported on registry enrollment; ichthyosis classification was determined from genotype-phenotype data. Race and ethnicity were included since prior ISS validations predominantly assessed White individuals.^3,4

Statistical Analysis

We characterized patients’ demographics using frequency and percentages. The χ² test was used for group comparison, and the t test was used to compare mean erythema and scale scores between groups. Intraclass correlation coefficients (ICCs) using the two-way random effects model were calculated to determine interrater reliability and ISS reliability in both groups. The two-way random effects model was used to generalize the reliability results to raters similar to the present raters.⁶ We report ICCs for absolute agreement and their 95% CIs, which assess whether raters assigned identical scores to the same set of photographs. ICC reliability was defined as poor (ICC <0.50), moderate (ICC 0.50-0.74), good (ICC 0.75-0.90), and excellent (ICC >0.90).

Analyses were conducted in March 2024 using SAS, version 9.4.3 (SAS Institute). P < .05 was deemed statistically significant.

Results

Patient Characteristics

The 47 photographs of Fitzpatrick I to III skin types came from 35 individuals: 2 (6%) were Hispanic, 1 (3%) was South Asian, 31 (89%) were White, and 1 (3%) was White and Hispanic; 18 (51%) were younger than 18 years and 17 (49%) were 18 years and older; and 20 (57%) were female and 15 (43%) were male (Table). The 47 photographs of Fitzpatrick IV to VI skin types came from 26 individuals: 1 (4%) was American Indian, 16 (62%) were Black, 4 (15%) were Hispanic, 1 (4%) was Pacific Islander, and 4 (15%) were South Asian; 10 (38%) were younger than 18 years and 16 (62%) were 18 years and older; and 12 (46%) were female and 14 (54%) were male.

Table. Individual and Photograph Characteristics.

Characteristic	No. (%)a		P value
	Fitzpatrick IV-VI skin types (n = 26)	Fitzpatrick I-III skin types (n = 35)
Age at photograph, y
<18	10 (38)	18 (51)	.31
≥18	16 (62)	17 (49)
Sex
Female	12 (46)	20 (57)	.40
Male	14 (54)	15 (43)
Race and ethnicity
American Indian	1 (4)	0	<.001b
Black	16 (62)	0
Hispanic	4 (15)	2 (6)
Pacific Islander	1 (4)	0
South Asian	4 (15)	1 (3)
White	0	31 (89)
White and Hispanic	0	1 (3)
Body part depicted in photograph
Dorsal feet	13 (28)	13 (28)	.99
Legs	13 (28)	14 (30)
Upper arm	11 (23)	10 (21)
Upper back	10 (21)	10 (21)
Ichthyosis classification
Erythrodermic phenotypes (eg, CIE)	2 (8)	9 (26)	.17
Erythrokeratoderma phenotypes (eg, EI)	5 (19)	7 (20)
Scale predominant (eg, LI)	19 (73)	19 (54)

Abbreviations: CIE, congenital ichthyosiform erythroderma; EI, epidermolytic ichthyosis; LI, lamellar ichthyosis.

^a There was no meaningful difference between the Fitzpatrick I to III skin type and Fitzpatrick IV to VI skin type groups with regard to age, sex, photograph body site distribution, and ichthyosis subtype distribution. There was a considerable difference in race composition between the 2 groups.

^b P < .05 was statistically significant.

Mean Scale and Erythema Scores

For individuals with Fitzpatrick I to III skin types, the mean (range) scale score was 2.49 (0-4.0) and erythema score was 1.94 (0-4.0). For individuals with Fitzpatrick IV to IV skin types, the mean (range) scale score was 2.50 (0-4.0) and erythema score was 1.88 (0-4.0). Differences in mean scale and erythema scores were not statistically significant (P < .86 and P < .32, respectively).

Interrater Reliability

In individuals with Fitzpatrick I to III skin types, interrater reliabilities for scale were excellent, ranging from 0.97 (95% CI, 0.93-0.99) to 0.99 (95% CI, 0.98-1.00). Interrater reliabilities for erythema were also excellent, ranging from 0.91 (95% CI, 0.79-0.97) to 0.95 (95% CI, 0.89-0.99).

In individuals with Fitzpatrick IV to VI skin types, interrater reliabilities for scale were excellent, ranging from 0.97 (95% CI, 0.93-0.99) to 0.99 (95% CI, 0.98-1.00). Interrater reliabilities for erythema were good and excellent, ranging from 0.90 (95% CI, 0.80-0.96) to 0.94 (95% CI, 0.86-0.98). Erythema of the legs had good reliability, while all other body sites showed excellent reliability.

Scale ICCs exceeded erythema ICCs across sites. Overlapping ICC 95% CIs between groups demonstrated no meaningful difference in ISS reliability across phototypes (Figure 2).

Figure 2. Intraclass Correlation Coefficients (ICCs) for Agreement for Erythema and Scale Among Raters.

Shaded areas indicate ICC reliability, which was defined as poor (ICC <0.50), moderate (ICC 0.50-0.74), good (ICC 0.75-0.90), and excellent (ICC >0.90).

Discussion

This study evaluated the ISS’s reliability in individuals with skin of color, addressing previous ISS validation limitations.^3,4 The results show robust interrater reliability for scale and erythema across phototypes, reinforcing the ISS as an inclusive ichthyosis severity tool.

ICCs for scale exceeded those for erythema likely because erythema can be masked by melanin. Nonetheless, this study shows that even in areas with greater baseline pigment and heavier scaling, such as the legs, erythema scoring maintained good reliability. This supports the ISS as an standardized severity tool even in populations where erythema assessment is more challenging.

Reliable, validated severity scoring informs treatment selection and evaluation of response and clinical trial eligibility. Individuals with skin of color remain underrepresented in dermatology clinical trials.⁷ Inclusive assessment tools like the ISS can help address this gap by capturing disease severity reliably across phototypes, facilitating equitable access to clinical trials. This is especially important in ichthyoses, as disease burden extends beyond physical symptoms to include psychosocial impacts.⁸ While objective erythema measurements using digital imaging and spectrophotometric techniques have been explored to address melanin masking challenges, a simple clinical assessment is needed in clinical practice.^9,10,11 The ISS offers a low-cost, easy-to-use tool that can be implemented across a wide range of settings.

Strengths and Limitations

With the rise of telehealth and photography-based trial enrollment, these results are timely. A strength of this study is the inclusion of all phototypes. However, variable photograph quality for individuals with Fitzpatrick IV to VI skin types limited validation to 4 sites, underscoring the need for appropriate lighting, full-body photographs, and well-focused images.

A broader limitation in dermatologic assessment tools remains the difficulty in visualizing erythema in pigmented skin. This may lead to disease severity underestimation and underdiagnosis.^12,13 While this study demonstrated no difference in mean erythema scores between groups, studies in cutaneous lupus and atopic dermatitis have shown that subjective erythema scores were lower for Black patients compared to White patients.^14,15 Although the ISS includes erythema assessment, this study did not use an objective tool to score erythema, such as spectrophotometry. This remains a critical area of investigation, as erythema-based inclusion criteria in trials may inadvertently exclude patients with skin of color if erythema is underrecognized. However, importantly, the ISS would still offer meaningful longitudinal assessment if within-patient changes are perceptible over time.

Conclusions

This cross-sectional study shows that validating the ISS in individuals with skin of color is a critical step toward ensuring that assessment tools fully capture disease severity, which is both a criterion for trial enrollment and a measure of therapeutic efficacy. Clinical trials have historically underenrolled individuals with skin of color, limiting generalizability of findings. This study supports the ISS as a reliable scoring instrument for ichthyosis severity across phototypes, providing a foundation for increasing diversity in clinical trials. The ISS’s accessibility, ease of use, broad applicability, and robust reliability underscore its role as the standard ichthyosis severity scoring tool.

Supplement.

Data Sharing Statement