Porokeratoma: A Different Entity or a Variant of Verrucous (Hyperkeratotic) Porokeratosis?

Abstract

Porokeratoma (acanthoma with features of porokeratosis) is a recently described entity with a distinct pattern of cornoid lamellation and clinically different from typical porokeratosis. We present a case of multiple porokeratomas on the buttock of a 78-year-old man with paraplegia secondary to poliomyelitis and ankylosing spondylarthritis. We briefly review the characteristics and controversies of this new entity.

Introduction

What was known?

Porokeratoma is a recently described entity that usually appears as a solitary verrucous lesion. It is still controversial if it is part of the spectrum of porokeratosis or if it represents a different entity.

The term porokeratoma (defined as an acanthoma with features of porokeratosis) was coined by Walsh, et al. in 2007 as a new entity with a distinct pattern of cornoid lamellation from typical porokeratosis.[1] We present a case of multiple porokeratomas and review their characteristics and controversies.

Case Report

A 78-year-old man, with paraplegia secondary to poliomyelitis and ankylosing spondylarthritis, presented with a 4-year history of slightly painful and slowly growing lesions on his left buttock. The patient had been unsuccessfully treated with cryotherapy 2 years before. Clostridiopeptidase and protease ointment had been occasionally applied. On physical examination, there were six well-defined verrucous lesions, with central depressions filled with keratotic material [Figure 1]. There were no other skin lesions and mucous membranes were not affected. An excisional biopsy of the largest lesion was performed. The lesion consisted of an acanthotic epidermis with low papillomatosis and overlying compact orthokeratosis [Figure 2]. Scattered throughout the lesion were multiple epidermal depressions containing cornoid lamella below which the granular layer was absent and dyskeratotic keratinocytes were identified [Figures 3 and 4]. Immunohistochemical studies for human papillomavirus resulted negative. The diagnosis of porokeratoma was made.

Figure 1.

Detail of three well-defined, non-confluent papular lesions, with central depressions filled with yellowish keratotic material on the left buttock

Figure 2.

Mild papillomatosis, slight acanthosis, and multiple epidermal depressions containing keratotic material (H and E, original magnification ×40)

Figure 3.

(a and b): Transition area between cornoid lamellae and orthokeratosis. Note the absence of granular cell layer and the dyskeratosis below the column of parakeratosis (arrow) (H and E, original magnification ×200)

Figure 4.

Detail of cornoid lamellae (H and E, original magnification ×200)

Discussion

Porokeratoma is a recently described type of acanthoma containing the characteristic feature of porokeratosis: The cornoid lamella.[1,2] It usually appears as a tumor-like lesion in patients without personal or familiar history of porokeratosis and without immunosuppressive conditions.[2] The most frequent locations are extremities, followed by head and neck, chest, buttocks, and intergluteal cleft.[1,2] Clinically, porokeratoma may be present as scaling plaques, papules, or nodules with central hyperkeratosis, but lesions can occasionally have verrucous appearance.[1] With respect to the case herein presented, we highlight the peculiar appearance mimicking a perforating disease.

Microscopically, porokeratoma shows orthokeratosis, acanthosis, occasional papillomatosis, and clear demarcation from normal skin. Multiple, broad, and confluent cornoid lamellae are disposed throughout the entire lesion, and not limited to the borders. Below the cornoid lamellae, dyskeratosis and loss of granular layer are evident. There is no central epidermal atrophy. Mild vascular dilatation with surrounding lymphoid cell infiltrate is usually seen within the superficial dermis.[1]

Cornoid lamella is an expression of focal abnormal cornification and it is regarded as an epithelial reaction pattern. Although it is classically seen in porokeratosis, it is not pathognomonic of this entity. Cornoid lamella can incidentally appear in other skin lesions such as actinic keratosis, seborrheic keratosis, scars, verruca vulgaris, milia, and squamous cell carcinomas or basal cell carcinomas.[1,3]

Although porokeratomas share a similar histological feature of cornoid lamellae, they are clinically and morphologically distinct from porokeratosis and its variants.[1] Lesions of porokeratosis present as scaling annular plaques of various sizes with ridge-like hyperkeratotic edges, central hypopigmentation, and atrophy. This clinical appearance is characteristic of porokeratosis and its all variants. In addition to differences in clinical presentation, porokeratomas differ from porokeratosis at the histological level since there is no central epidermal atrophy, and the cornoid lamellae are embedded throughout the entire horny layer instead of being present only at the borders.[2]

Porokeratoma has been included in a long list of terms such as hyperkeratotic porokeratosis, genitogluteal porokeratosis, follicular porokeratosis, and more commonly porokeratosis ptychotropica. Verrucous porokeratosis has been proposed to unify all these terms.[4] Clinically, these cases of verrucous porokeratosis frequently show psoriatic-like plaques in butterfly-shape on the buttocks surrounding the anus and occasional satellite lesions.[4,5] Histopathologically, there are multiple concentric cornoid lamellae over a digitate epidermis.[4,6] Although both entities share the presence of multiple cornoid lamellae, lesions of porokeratoma clinically and histologically differ from verrucous (hyperkeratotic) porokeratosis.

The majority of previous reported cases of porokeratomas have been solitary, except for a case reported by Kanitakis, et al. who incidentally also had ankylosing spondylarthritis similar to the case presented herein.[2] To the best of our knowledge, our patient represents the second case with multiple porokeratomas and ankylosing spondylarthritis; therefore, we agree with Kanitakis, et al. that there is a possibility of an association between these two entities. Although many cases of porokeratosis have been associated with immunosuppression, heretofore, none of the cases of porokeratomas have similarly shown this association.[2]

Malignant neoplasms have been reported in different clinical variants of porokeratosis, being squamous cell carcinoma the most frequently observed.[4,7] Due to the similarities with porokeratosis, it has been suggested that porokeratoma may also have potential for malignant transformation; therefore, although malignant transformation has not yet been reported in porokeratomas, excision and close follow-up is indicated in patients with porokeratomas, especially if they are immunocompromised.[1,2,4]

In conclusion, we have presented a case of multiple porokeratomas in a patient with ankylosing spondylarthritis. This association has been previously reported. Although, so far, the terminology is not clearly defined, we agree that porokeratoma probably represents a completely different form of porokeratosis.

What is new?

1. Clinical and histopathological findings suggest that porokeratoma represents a different entity from porokeratosis.

2. Association of porokeratoma with ankylosing spondylarthritis may probably be more than a casual finding.