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

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.

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

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.

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

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.

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.