Clinical features, histology, and treatment outcomes of granular parakeratosis: a systematic review

BACKGROUND: Granular parakeratosis is a rare disorder characterized by erythematous‐brown hyperkeratotic papules and erythematous patches with scaling, occurring predominantly in the flexures and sites of occlusion. While the exact underlying pathogenesis remains unknown, there has been a wide variety of precipitating factors and treatment options reported in the literature. OBJECTIVE: We systematically reviewed and identified precipitants of granular parakeratosis, as well as its clinical and histologic features and treatment outcomes. METHOD: A comprehensive literature search was conducted using MEDLINE and Embase in March 2021. RESULTS: A total of 60 studies with 129 patients were included for analysis. An inciting factor was identified in 53.4%, the most common being topical agents including zinc oxide (17.1%), deodorant/antiperspirant (15.5%), and those containing benzalkonium chloride (7.0%). The majority presented with bilateral (68.2%) eruption of hyperkeratotic papules or erythematous patches and plaques, most frequently involving the axilla (56.5%). The prevailing histologic feature was retained keratohyalin granules within the stratum corneum in punch biopsy (97.2%) and curette (100%) specimens. Treatment options with reported success ranged from topical corticosteroids and systemic antibiotics to surgical interventions. CONCLUSION: We provide a systematic review of reported precipitants, clinical features, and treatment options that clinicians should consider when granular parakeratosis is considered.