# Mosaic Darier's Disease: A Case of Unilateral Localized Type I Segmental Darier's Disease

## TL;DR

A rare case of unilateral Darier's disease is described, highlighting its unique presentation and diagnosis.

## Contribution

This paper presents a rare case of type I segmental Darier's disease with unilateral distribution and confirms the diagnosis through histopathology.

## Key findings

- The patient's lesions followed Blaschko's lines and worsened with heat, consistent with segmental Darier's disease.
- Histopathology confirmed classic features of Darier's disease, including acantholysis and dyskeratosis.
- Treatment with corticosteroids and salicylic acid improved symptoms without isotretinoin due to fertility considerations.

## Abstract

Darier's disease (DD), also known as Darier‐White disease, is a rare autosomal dominant genodermatosis resulting from mutations in the ATP2A2 gene. It commonly manifests as keratotic papules or plaques in seborrheic areas and is often triggered by heat, sweating, and trauma. A rare mosaic variant, segmental Darier's disease, occurs due to post‐zygotic mutations and presents along Blaschko's lines. We describe a 41‐year‐old male presenting with pruritic, hyperpigmented, keratotic papules distributed unilaterally on the left trunk and upper thigh. The lesions, following Blaschko's lines, worsened with heat. There was no family history of similar conditions. Histopathology revealed classic features of Darier's disease, including irregular acantholysis, dyskeratosis with corps ronds and grains, and suprabasal acantholysis, confirming the diagnosis of type I segmental Darier's disease. Treatment involved corticosteroids twice daily, salicylic acid 2% gel for hyperkeratosis, and lifestyle modifications. Isotretinoin was avoided due to fertility plans. This case highlights the distinctive presentation of type I segmental Darier's disease and underscores the importance of accurate diagnosis through clinical and histopathological correlation. Increased awareness of this rare condition is crucial for timely diagnosis, effective symptom management, and tailored treatment strategies.