Punctate Porokeratosis Palmaris et Plantaris.

Porokeratosis, a keratinization disorder, is probably a group of unrelated conditions with same distinctive histological appearance, featuring cornoid lamellae. A case of punctate porkeratosis in a 24 year old male patient is reported for its rarity.

What was known?

Porokeratosis, a keratinization disorder is not uncommon. However, porokeratosis affecting the palms and soles is rare.

Introduction

Porokeratosis, a keratinization disorder, is probably a group of unrelated conditions with same distinctive histological appearance, featuring cornoid lamellae.[1] Many clinical variants are described, of which punctate porokeratosis (PP) is a less often encountered condition.

Case Report

A 24-year-old male patient presented with multiple, tiny, 1-2 mm hyperkeratotic, spine like papules on both the palms and soles, of 3 years duration [Figures 1 and 2]. Papules were mainly seen in the palmar creases and were essentially asymptomatic. The lesions were moderately tender, on vertical pressure, only, when he tried to lift heavy objects. He had only a single lesion in each sole. He did not have lesions elsewhere on the body.

Figure 1

Multiple, tiny, 1-2 mm hyperkeratotic, spine like papules on both the palms

Figure 2

1-2 mm hyperkeratotic, spine like papules on the sole

The patient was born of a non-consanguineous marriage and his parents and other siblings were unaffected. However, his maternal aunt and her daughter had similar complaints. Routine biochemical and hematological investigations were not contributory.

A clinical diagnosis of punctate palmoplantar keratoderma was considered and a biopsy from a palmar lesion was carried out. However, HPE revealed the typical appearance of porokeratosis [Figure 3].

Figure 3

(a) and (b) Focal area of disruption of the granular layer, with a column of parakeratotic cells in the stratum corneum—the Cornoid lamella [×10 [Figure 3a] ×20 [Figure 3b] and ×40 [Figure 3c]

Discussion

In 1893, Mibelli first described what is now considered as classic porokeratosis. Guss, in 1971, was the first to report porokeratosis palmaris et plantaris disseminata (PPPD). In 1977, Rahbarin proposed that PP be added to the group of diseases already classified as variations of porokeratosis.[2] However, this opinion was disputed by Guss et al.[3]

Porokeratosis is sometimes inherited as an autosomal dominant disorder, but most cases appear to be sporadic.[2] Involvement of many family members of the present patient, favors an autosomal dominant mode of inheritance, though his immediate family members were spared.

Five different forms of porokeratosis are described, that is, the plaque type, disseminated superficial actinic porokeratosis (DSAP), linear porokeratosis, PPPD and PP[4] though, Guss et al. considered PP and PPPD as a single entity.[3]

PPPD is characterized by the appearance in adolescence or early adult life of many lesions on the palms and soles and subsequently by the involvement of other areas of the body with large numbers of small superficial lesions.[5] Our patient also developed the palmar papules in early adult life. Though PP may resemble PPPD, absence of involvement of other parts of the body ruled out PPPD in the present case, if these two entities were to be considered different conditions.

The palmar/plantar papules were moderately tender to pressure in our patient, as reported by other authors.[6]

Clinical differential diagnosis is from punctate keratoderma, arsenical keratoses, Cowden's disease, Darier's disease, warts and nevoid basal cell carcinoma syndrome. However, biopsy is conclusively similar to our experience. Though clinically an erroneous diagnosis of punctate palmoplantar keratoderma was considered, HPE revealed the typical features of porokeratosis.

Although many clinical variants are described, histology is more or less similar to Porokeratosis of Mibelli, but less pronounced.[7] However, in our patient, the HPE changes were very characteristic and typical. Porokeratosis is considered a disorder of keratinization, but the definitive pathogenesis remains unclear. Reed proposed that the characteristic Cornoid lamella represents the border between normal epidermis and an expanding mutant clone of cells. Another view is that porokeratosis represents an immunological response to an unidentified epidermal antigen that provides a mitotic stimulus for epidermal cells.[8]

Histologically, a focal area of disruption of the granular layer, with a column of parakeratotic cells in the stratum corneum—the Cornoid lamella is pathognomonic of porokeratosis, which was typically observed in HPE in the present patient. The presence of a clone of abnormal epidermal cells located at the base of the parakeratotic column explains the lesions of porokeratosis. Other conditions characterized by Cornoid lamellae are verruca vulgaris, actinic keratosis and porokeratotic eccrine ostial and dermal ductal nevus (PEODDN). Koilocytosis in addition to histological features is found in verruca vugaris, while epidermal cytologic atypia is seen in actinic keratosis. Both such changes were not observed in the present case. HPE of PEODDN shows epidermal invaginations containing cornoid lamella that involves the eccrine ducts which was not noted in the present case. There are reports in literature where the cornoid lamella involves eccrine ducts and hair follicles.[91011]

Porokeratosis was erroneously named so, because the column of parakeratosis known as cornoid lamella was initially described as being present over a sweat pore, which is a fixed structure that cannot expand peripherally.[2]

Overexpression of the P53 tumor suppressor protein has been found in porokeratosis.[12] Due to lack of facilities, such studies could not be undertaken.

The various treatment modalities available are, cryotherapy, other destructive measures for limited lesions, acitretin or PUVA (except for DSAP).[1] Topical 5-flourouracil solution or cream has also been used.[1013] In the present case, the patient showed significant improvement with topical salicylic acid and retinoic acid-0.25% in 8 weeks.

What is new?

Porokeratosis is a keratinization disorder encompassing a group of unrelated conditions with distinctive histological appearance, featuring cornoid lamellae. Punctate porokeratosis (PP) is rare and can be mistaken for punctuate keratoderma, clinically, as in the present case where HPE clinched the correct diagnosis, thus highlighting the significance of HPE in dermatology.