# Unveiling a Therapeutic Breakthrough: Baricitinib in the Treatment of Acute and Recurrent Pustulosis Associated with Atopic Dermatitis—A Case Report, Literature Review, and Novel Clinical Insights

## TL;DR

A 40-year-old woman with a rare skin condition called ARP and atopic dermatitis showed significant improvement after treatment with Baricitinib, suggesting shared inflammatory pathways and new therapeutic possibilities.

## Contribution

This case report is the first to document ARP coexisting with atopic dermatitis and demonstrates the efficacy of Baricitinib in treating both conditions.

## Key findings

- Baricitinib treatment led to marked improvement in both ARP and atopic dermatitis symptoms.
- ARP may have a subtype triggered by heat and sweat, not just UV radiation.
- Shared inflammatory pathways between ARP and atopic dermatitis suggest potential for JAK inhibitors in treatment.

## Abstract

Acute and recurrent pustulosis (ARP), previously known as actinic folliculitis, superficial actinic folliculitis, or even acne aestivalis, is a rare, underdiagnosed dermatological condition characterized by the sudden onset of monomorphic pustular eruptions on an erythematous background localized predominantly on the upper body. While typically associated with sun exposure, ARP can also be triggered by other factors, such as heat or sweating, underscoring its multifactorial etiology. We report the case of a 40-year-old woman with ARP, presenting diagnostic challenges due to overlapping clinical features and the coexistence of atopic dermatitis (AD), an association not previously documented in the literature. The patient exhibited recurrent pustular episodes localized on sun-exposed and non-exposed areas, unresponsive to conventional therapies. Comprehensive microbiological, histopathological, and clinical assessments excluded infectious, drug-induced, and other inflammatory pustular dermatoses, confirming the diagnosis of ARP. Importantly, treatment with Baricitinib, a Janus kinase (JAK) inhibitor primarily prescribed for AD, resulted in marked improvement in both conditions, suggesting shared inflammatory pathways. This therapeutic response highlights the potential role of JAK inhibitors in ARP management, particularly in cases resistant to standard interventions. This report also proposes the inclusion of heat- and sweat-induced ARP as a distinct subtype, expanding the understanding of its diverse triggers beyond UV radiation. Furthermore, it underscores the need for standardized diagnostic criteria and a structured approach to differential diagnosis, given the condition’s underdiagnosed and often misinterpreted nature. By shedding light on the clinical and therapeutic aspects of ARP, this case contributes to a more nuanced understanding of this rare entity and its potential interplay with inflammatory skin disorders such as AD.