Linear porokeratosis with follicular involvement.

Sir,

Porokeratosis,[12] first described in 1893 by Mibelli, is a heterogeneous group of disorders of abnormal keratinization and affects the keratinous tissue, with variety of clinical presentation and potential for malignant transformation.[3] Exact heritable pattern has not been identified. It appears in infancy or childhood and boys are more frequently affected. Besides different clinical subtypes, e.g., porokeratosis of Mibelli (PM), disseminated superficial, disseminated superficial actinic porokeratosis (DSAP), linear porokeratosis, porokeratosis palmaris et plantaris disseminata (PPPD), palmo-planter punctate porokeratosis (PPPP), other varieties like pustular, pruritic papular, verrucus/porokeratosis ptycotropica, giant, follicular, bullous, hypopigmented and erosive, have been described. Exact pathogenesis is not known but an abnormal early keratinocyte apoptosis accompanied by dysregulation of terminal differentiation (keratinization) has been suggested for pathogenesis of cornoid lamella.[4] Development of the invasive squamous cell carcinoma, basal cell carcinoma and Bowen disease has been reported in all variants except punctate porokeratosis. Linear porokeratosis is particularly more susceptible to malignant degeneration.[1-3]

A 27-year-old female presented with asymptomatic small, elevated skin lesions on right upper limb. Lesions gradually increased in number and size over the period of 1 year. Cutaneous examination revealed multiple well-defined, brown-black to skin color papules and annular lesions with peripheral keratotic ridges [Figure 1], distributed linearly on flexure side of right upper arm, forearm, shoulder and axillae. Palms, soles and other body areas were free from lesions. There was no family history of similar lesion. Histopathology of skin biopsy showed cornoid lamella which is a column of tightly packed parakeratotic cells with pyknotic nuclei in epidermis and absence of granular layer below cornoid lamella. Here, cornoid lamella was localized to hair follicle [Figures 2 and 3]. Although cornoid lamella is a classical feature of porokeratosis, it may be seen in viral warts, icthyosis and other nevoid hyperkeratotic conditions.

Figure 1

Papules and annular lesions (border stain with Giemsa stain) on forearm

Figure 2

Tightly packed parakeratotic cells with pyknotic nuclei extending into hair follicle and absence of granular layer (H and E stain, ×400)

Figure 3

Parakeratotic cells involving hair follicle (H and E stain, ×400)

Clinically, various stains like gentian violet, povidone-iodine and Giemsa have been used to stain cornoid lamella. Paint the suspected lesion/s with stain, then remove the stain with alcohol; elevated keratotic ridge retains the stain and is helpful in clinical differentiation from seborrheic keratoses, stucco keratoses, disseminated granuloma annulare, atrophic annular lichen planus.[5]

Irrespective of clinical presentation, histopathological features of all subtypes are identical and include cornoid lamella along the peripheral rim. Cornoid lamella is most prominent in PM. Besides keratotic ridge, cornoid lamella may involve hair follicle as well as acrosyringium. Follicular localization of cornoid lamella is uncommon and described only in association with other subtypes such as DSAP, PM, and exclusive follicular cornoid lamella in follicular porokeratosis.[6-8] Follicular and non-follicular epidermal involvement may be due to multifocal origin of the abnormal keratinization within involved epidermis. It is not known whether lesion starts primarily form hair follicle or there is secondary involvement of follicular epidermis. Clinically involvement of hair follicle has been described in DSAP and PM.[7]

Linear porokeratosis[12] is a rare genetically determined disorder with a characteristic linear distribution and can appear at any age. Lesions may arise in infancy or childhood but the onset may be delayed and has a tendency for malignant transformation. Malignant transformation[3] is as high as 19% in linear porokeratosis, while in other types it ranges from 3 to 10%. Linear porokeratosis exists in two forms: In the more common localized form, lesions are unilateral, confined to one extremity and frequently distal in localization. In the rare generalized form,[9] lesions are multiple, affect several extremities and involve the trunk. In the present case of localized form of linear porokeratosis, cornoid lamella is localized to follicle as well as non-follicular epidermis. To the best of our knowledge, follicular localization of cornoid lamella in linear porokeratosis is rare and has been reported recently in a few case studies.[10]

Our patient was treated with topical 5-fluorouracil and advised protection from sunlight. Many drugs including topical 5-fluorouracil, calcipotriol, 5% imiquimod and oral retinoid (Acitretin) have been found effective in the treatment of porokeratosis. Surgical treatments like cryotherapy, dermabrasion, CO2 laser ablation, shave and curettage, photodynamic therapy, electrodessication, 585 nm flashlamp-pumped pulsed dye laser and frequency-doubled Nd:YAG laser are shown to be helpful in linear porokeratosis. Although topical Diclofenac (3% gel) is found to exert strong anti-neoplastic effects by inducing apoptosis of malignant cells, it is not found effective in the treatment of porokeratosis, but may have a role in prevention of malignancy.[11] Protection from sun light/UV radiation and periodic examination of patient for early detection of the malignant changes is mandatory.