CPC07 Lines of evidence: unravelling a case of blaschkoid Darier disease

Abstract Blaschkoid Darier disease is a rare variant of Darier disease characterized by lesions following Blaschko’s lines, often presenting in a segmental distribution. Differentiating it from inflammatory linear verrucous epidermal naevus (ILVEN) can be challenging due to overlapping clinical and histopathological features. A 41-year-old woman presented with a 6-year history of a persistent papular rash localized to her right abdomen, flank and back. She reported no systemic symptoms, no mucosal or genital involvement, and no significant personal or family medical history. Previous treatments with emollients and topical steroids had been ineffective. On examination, a papular eruption was noted, following a blaschkoid distribution. A diagnostic punch biopsy revealed dyskeratotic keratinocytes overlying areas of epidermal hypergranulosis and acantholysis. The initial histopathological assessment suggested ILVEN. However, given the late-onset presentation in her late 30s and the histological presence of acantholysis, the diagnosis was reconsidered during a multidisciplinary dermatopathology meeting. The consensus favoured a diagnosis of blaschkoid Darier disease. The patient was initiated on fusidic acid–betamethasone cream, showing a strong early clinical response. Blaschkoid Darier disease is typically a segmental manifestation arising from postzygotic mutations in the ATP2A2 gene. Unlike ILVEN, which often presents in childhood and lacks acantholysis, blaschkoid Darier disease typically manifests later in life and shows acantholytic dyskeratosis on histology. Accurate differentiation is crucial for guiding appropriate treatment strategies. This case underscores the importance of correlating clinical presentation with histopathological findings and considering blaschkoid Darier disease in adults with unilateral, blaschkoid rashes. Multidisciplinary discussion played a pivotal role in achieving the correct diagnosis and guiding effective management.