Introduction

Trichilemmal keratosis, or trichilemmal horn, is a potentially underrecognized morphologic growth pattern that arises from the outer root sheath of the hair follicle and is characterized by abrupt trichilemmal maturation of keratinocytes in the absence of a granular layer [1]. It represents a proliferation of follicular epithelium with trichilemmal differentiation [2]. Clinically, it forms a horn-like, compact vertical column of keratin extending from a follicular structure. This lesion shows a female predominance, accounting for approximately two-thirds of reported cases [2,3]. While trichilemmal keratosis has been described in patients aged 16 to 83 years, it is most frequently seen in individuals over 50 years of age [3]. Trichilemmal keratosis may resemble a cutaneous horn arising from premalignant or malignant epidermal lesions such as seborrheic keratosis, hypertrophic actinic keratosis (HAK), keratoacanthoma, and squamous cell carcinoma. However, attention to the clinical context, including patient age, lesion location, and growth pattern, may provide useful diagnostic clues. Accurate recognition is important because trichilemmal keratosis may be mistaken for premalignant or malignant keratinizing lesions, potentially leading to unnecessary treatment. We report this case to highlight the diagnostic challenge and emphasize the inclusion of trichilemmal keratosis in the differential diagnosis of hyperkeratotic cutaneous lesions.