# Comment on: Proposal for a new diagnostic classification of photodistributed Stevens–Johnson syndrome and toxic epidermal necrolysis

## TL;DR

This paper comments on a new classification for Stevens–Johnson syndrome and toxic epidermal necrolysis, suggesting that blood supply reduction due to skin pressure explains the photo-distribution pattern.

## Contribution

The paper proposes an alternative explanation for the photo-distribution pattern in SJS/TEN based on localized blood supply reduction.

## Key findings

- A review of cases in the IMARI-SA register showed a similar clinical pattern to McKinley et. al.'s findings.
- Localized skin pressure reduces blood supply, limiting T lymphocytes and cytokines that cause SJS/TEN.
- The relative sparing of some skin areas is attributed to this localized blood supply reduction.

## Abstract

Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and SJS/TEN overlap (SJS/TEN), collectively referred to SJS/TEN, form a spectrum of severe life-threatening adverse drug reactions whose pathomechanism is not fully understood. The article "Photodistributed Stevens–Johnson Syndrome and Toxic Epidermal Necrolysis: A Systematic Review and Proposal for a New Diagnostic Classification" by McKinley et. al., discusses a distinct distribution of epidermal necrosis in SJS/TEN, attributable to preceding exposure to ultraviolet radiation (UVR), and relative sparing of photo-protected areas. After reviewing numerous cases within the Immune-mediated Adverse drug Reactions in African HIV endemic setting Register and Biorepository (IMARI-SA) at the University of Cape Town with a similar clinical pattern as those published by McKinley et. al., we propose that the relative sparing of some areas giving an impression of photo-distribution is due to localised increase in skin pressure that reduces the blood supply in that area below a critical threshold. A dip in blood supply below this critical threshold quantitively limited T lymphocytes and cytokines that drive SJS/TEN to reach and damage the skin.