The human papilloma virus most frequently causes infectious etiology resulting in a verruca vulgaris. Molluscum contagiosum of the poxvirus group occasionally has formed a cutaneous horn. The only other infectious cause has been leishmaniasis. Benign idiopathic causes are frequent and include seborrheic keratosis, epidermal nevus, trichilemmal cyst, trichilemmoma, prurigo nodule, and intradermal nevus. One report of discoid lupus erythematosus at the base of a cutaneous horn exists.
Diagnosis is confirmed with a skin biopsy.
An adequate specimen usually can be obtained with a simple shave biopsy. The specimen must be of sufficient depth to ensure that the base of the epithelium is obtained for histologic examination. The horn is composed of compacted hyperkeratosis and parakeratosis. The lesion at the base will display features characteristic of the pathologic process responsible for the development of the horn. Treatment recommendation is contingent upon the type of lesion at the base.