Nail Unit Involvement in a Porokeratosis‐Spectrum Lesion Exhibiting Porokeratotic Adnexal Ostial Nevus‐Like Features: Expanding the Clinical Spectrum

ABSTRACT

Porokeratotic Adnexal Ostial Nevus (PAON) is an uncommon disorder characterized by abnormal keratinization affecting eccrine and follicular adnexa. Initially described separately as porokeratotic eccrine ostial and dermal duct nevus and porokeratotic eccrine and hair follicle nevus, the term PAON was introduced in 2009 to encompass these conditions. PAON presents with diverse clinical manifestations, ranging from asymptomatic keratotic papules and plaques to verrucous lesions. Typically appearing at birth, PAON can rarely manifest in adulthood. We report a case of a porokeratosis‐spectrum lesion with features overlapping with PAON in a male patient in his 30s presenting with longitudinal splitting of the left thumbnail associated with an erythematous linear lesion extending from the nail matrix, alongside a scaly plaque on the proximal nail fold and dorsal thumb. This case highlights the importance of considering porokeratosis‐spectrum disorders, including lesions with PAON‐like features, in the differential diagnosis of monodactylous erythronychia and onychodystrophy, particularly due to its potential for subtle cutaneous involvement as was present in this case. This instance represents a rare presentation of a porokeratosis‐spectrum lesion involving the nail unit epithelium and contributes to the expanding clinical spectrum of porokeratosis with PAON‐like features.