A case of localized, unilateral hyperkeratosis lenticularis perstans on a woman's breast

A 75-year-old woman presented with a 5-year history of asymptomatic lesions confined to the right breast, which caused her discomfort when wearing a bra. The patient denied any injury or trauma to the affected area. Clinical inspection showed three plaques, each of them formed by several yellowish keratotic adherent papules. The individual papules measured 1 to 2 mm in diameter, and consisted of isolated or contiguous monomorphic elements, ranging from 50 to 60 per plaque. Some of these elements were more elevated than others or showed a slight depression at their center (Figure 1). A biopsy taken from one of the plaques revealed a laminar orthokeratotic and hyperkeratotic lesion, strongly eosinophilic at its center, thus representing a contrast to the normal basket-weave stratum corneum on both sides. The epidermis below the lesion showed a loss of the rete ridges. Towards the edges of the lesion, the epidermis formed papillomatous elevations similar to a church spire. In the dermis, there was a slight perivascular lymphohistiocytic inflammatory infiltrate (Figure 2). Topical treatments including calcipotriene and urea were unsuccessful. Eventually, the lesions were removed using electrocautery and curettage. There was no recurrence. Also known by its eponym (Flegel’s disease), hyperkeratosis lenticularis perstans (HLP) is a rare disorder of keratinization described by Flegel in 1958. Most cases are sporadic in origin, although it is typically described as an autosomal dominant disorder. In some series, the minority of cases was familial [1, 2]. It characteristically affects middle-aged or older men, with bilateral lesions mainly found on the back of the feet and the anterior aspects of the legs. More rarely, the disorder has been described on the upper extremities and, as an exception, also in other locations. Clinically, it is characterized by multiple red-brown papules almost symmetrically located on the dorsum of the feet and legs. The typical HLP lesion is a well-defined red to yellow-brown papule, about 2 to 5 mm in diameter, with a keratotic adherent scale. Occasionally, it has been described involving the upper extremities [1], hands [3], back [4], ears [1], palms [5], and oral mucosa. More rarely, lesions in the axillary folds, antecubital and popliteal fossae, and on the eyelids have been reported, in addition to the more common involvement of legs and hands [6]. A case with unilateral lesions on the lower extremity – existing since puberty – has also been described [7]. Histopathologic findings characteristically show an orthokeratotic and hyperkeratotic epidermis of decreased thickness. The dermis exhibits a lymphocytic infiltrate of