Spiky Papules on the Dorsal Feet

The Diagnosis: Hyperkeratosis Lenticularis Perstans (Flegel Disease)

Hyperkeratosis lenticularis perstans, also known as Flegel disease, is a rare dermatosis first described by Flegel¹ in 1958. This benign disorder is characterized by multiple asymptomatic 1- to 5-mm keratotic papules in a symmetric distribution favoring the dorsal aspects of the feet and distal extremities in adults. An autosomal-dominant inheritance pattern has been postulated, though many cases sporadically occur.² The characteristic spiky papules typically appear during mid to late adulthood and tend to persist. Treatment options are lacking, with reports of partial or no response to topical calcipotriol, topical 5-fluorouracil, cryotherapy, and topical and oral retinoids.^3,4

The histopathology of hyperkeratosis lenticularis perstans is distinct, showing a central discrete area of orthohyperkeratosis with patchy parakeratosis flanked by a normal stratum corneum. The underlying epidermis typically shows effacement of the rete ridge pattern with subtle basal zone vacuolization and rare necrotic keratinocytes with an underlying lichenoid infiltrate within the papillary dermis comprised of lymphomononuclear cells.

In contrast, punctate porokeratosis clinically tends to involve the palms and soles, though the arms and legs also may be involved. This entity tends to occur during adolescence. A raised hyperkeratotic papule clinically is present. Histopathologically, the epidermis has a cup-shaped depression filled with hyperkeratosis and a column of parakeratosis (coronoid lamellae)(Figure 1).

Figure 1. Punctate porokeratosis. Hyperkeratotic papule with parakeratosis (H&E, original magnification ×20).

Acrokeratosis verruciformis of Hopf clinically appears on the dorsal aspects of the hands and feet as small warty papules in association with Darier disease. It typically presents during early childhood. Histopathology shows tiered hyperkeratosis, papillomatosis, and acanthosis (Figure 2).

Figure 2. Acrokeratosis verruciformis of Hopf. Hyperkeratosis, papillomatosis, and acanthosis (H&E, original magnification ×100).

Perforating granuloma annulare presents on the dorsal aspects of the hands and fingers as scaly papules with either central umbilication or keratotic plugs. Histopathology shows transepidermal elimination of degenerated collagen (Figure 3).

Figure 3. Perforating granuloma annulare. Transepidermal elimination of degenerated collagen (H&E, original magnification ×40).

Stucco keratoses present on the dorsal aspects of the feet and ankles but are waxy smooth papules as opposed to hyperkeratotic spiky papules. Histologically, they are characterized by retention hyperkeratosis with lack of parakeratosis and regular acanthosis with a "string sign" indicating that the lesion extends to a uniform depth. (Figure 4).

Figure 4. Stucco keratosis. Retention hyperkeratosis and regular acanthosis with a “string sign” (H&E, original magnification ×40).