Linear Porokeratosis: An Unusual Presentation

Sir,

Linear porokeratosis is listed as a rare disease by the Office of Rare Diseases (ORD) of the National Institutes of Health, which means that affects fewer than 20000 people in the US. In India also, very few cases of linear porokeratosis have been reported.[1]

Linear porokeratosis is a disorder that is characterized clinically by sharply demarcated hyperkeratotic annular lesions with distinct keratotic edges corresponding histologically to the presence of cornoid lamella. Of the five types, linear porokeratosis is the rarest. The unilateral linear form resembles linear verrucous epidermal nevus. It has an autosomal dominant mode of inheritance and affects men twice as often as women.[2]

We present a 12-year-old female with asymptomatic, nonpruritic, hyperpigmented annular plaques in a linear and grouped array over the entire length of her right lower limb along the line of Blaschko. One lesion measured 25 × 2 inches, extending from the lateral malleolus to the mid-thigh on the right lower limb; there were a few discrete lesions present on the gluteal region also [Figures 1 and 2].

Figure 1.

Asymptomatic linear porokeratotic lesion measuring approximately 25 × 2 inches over the right lower limb

Figure 2.

Grouped annular lesion with broad base over the right mid-thigh

No other area was involved. There were no hair or nail changes. Systemic examination is normal. There was no history of consanguinity, and there was no family history of any similar disease.

The lesion, which initially started as grouped annular plaques over the lateral side of the right ankle in childhood, gradually extended upwards in linear fashion up to the mid-thigh, with some lesions also occurring in the gluteal region.

Histological examination of biopsy from the edge of the hyperkeratotic annular lesion showed parakeratotic column of cells (cornoid lamella) traversing the stratum corneum and a thin granular epidermis [Figures 3 and 4].

Figure 3.

Porokeratosis: parakeratotic column of cells (coronoid lamella) (hematoxylin and eosin; 10×)

Figure 4.

Porokeratosis: parakeratotic column of cells (coronoid lamella) with markedly attenuated granular layer hematoxylin and eosin; 45×)

This case is reported for its rarity as well as the unusual presentation; the lesion had broad base and there was involvement of nearly the entire limb. This is the longest linear porokerototic lesion to be reported to date.