Cutaneous ossification is an unusual event that may be primary or secondary to either inflammatory or neoplastic processes. It is classified as primary when it occurs in the absence of a demonstrable preexisting lesion. Secondary lesions have been most commonly reported occurring with pilomatricoma, basal cell carcinoma, acne vulgaris, and melanocytic nevi (nevus of Nanta). Histologically, the osteomas are composed of well-formed bony spicules with prominent cement lines and calcification. They may demonstrate osteoblasts, osteoclasts, and osteocytes and occasionally may even demonstrate bone marrow elements. We searched the files of a reference dermatopathology laboratory to identify cases of either primary or secondary cutaneous ossification. We present a series of 74 cases of primary and secondary cutaneous ossification. Most cases were secondary in nature. Lesions were more common on the head and neck and in whites. Lesions were also more commonly identified in female patients. In addition, included in our series are 19 cases of nevus of Nanta. To our knowledge, this represents the largest series of such cases in the English literature. Cutaneous ossification is seen both in primary and, more commonly, in secondary conditions involving the skin. Benign neoplasms, especially melanocytic nevi, represent the most common cause of secondary osteoma formation. Women are more commonly affected than men, but the reason for this is unclear. The exact reason why osteoma formation occurs is unclear and requires further study.

Epidermolytic hyperkeratosis (EH) is a unique histopathologic alteration of the skin characterized by hyperkeratosis with perinuclear vacuolization of keratinocytes primarily in the stratum granulosum and the stratum malpighii. It is seen as an incidental finding in a variety of conditions, benign and malignant, as well as sporadic and familial. Recently, it has been reported that EH may be associated with dysplastic nevi (nevus with architectural disorder [NAD]). Cases of melanocytic nevi with epidermolytic hyperkeratosis were retrieved from the files of a referral dermatopathology laboratory over a 6-year period. We present a series of 53 cases of EH in both ordinary nevi and NAD. Epidermolytic hyperkeratosis identified in association with NAD accounted for 46 cases or 86.8% of the total lesions while ordinary nevi represented 7 or 13.2% of total cases. Our study confirms that the incidence of EH is higher in association with dysplastic nevi than in ordinary melanocytic nevi and may serve as a marker for NAD, but with lower sensitivity and only moderate specificity.