Porokeratoma: A distinct variant of porokeratosis

Follicular Porokeratoma: Report of a New Variant of Porokeratoma (Porokeratotic Acanthoma) and Literature Review

“…PKM has various clinical presentations but usually presents as an asymptomatic, slowgrowing keratotic or verrucous nodule, occasionally of large size. 10,11 It is usually single (74%), but 6 patients had more than one lesion, [2][3][4]7,10,12 occasionally in a bilateral distribution. PKM most commonly develops on the limbs (lower: 41% and upper: 23%), the buttocks (18%), the face (lip and forehead), or the trunk (each location: 9%).…”

“…Interestingly, the case presented here comprised CL embedded in hair follicle infundibula, a finding that was very recently reported in one case of PKM. 11 This is reminiscent of the rare cases of follicular PK, a PK variant with CL present exclusively within hair follicles. [14][15][16][17] By analogy with these rare PK forms, we have termed this case "follicular PKM."…”

“…Amyloid deposits were found in one case, 8 as can be occasionally seen in classical PK forms, 13 and a lymphocytic dermal infiltration with hemosiderin deposits may be present. 11 PKM, therefore, shares with the classical PK forms the presence of CL but differs from them histologically because CL are multiple, embedded within the hyperplastic epidermis and because the epidermis between CL is hyperplastic, contrasting with the usual PK forms where the epidermis may be atrophic, normal, or only slightly thickened; furthermore, the clinical appearance of PKM (verrucous nodule) is distinct from that of the common PK forms, which usually manifest as annular plaques with a keratotic rim. Interestingly, the case presented here comprised CL embedded in hair follicle infundibula, a finding that was very recently reported in one case of PKM.…”

“…Hair follicle involvement is characteristic of a specific type of PK referred to as “follicular PK.” Similar to our case, follicular involvement has been observed in only one case of PKM. 11 Therefore, we consider this lesion as a new variant of PKM associated with hair follicles, which we termed follicular PKM, by analogy to follicular PK. We present a review of all published cases of PKM.…”

“…Porokeratoma (PKM), also known as porokeratotic acanthoma, is a rare, specific type of acanthoma that was first described in 2007, 1 of which 22 cases have been reported so far. [1][2][3][4][5][6][7][8][9][10][11] It manifests clinically as a well-circumscribed keratotic papulonodule and is characterized histologically by the presence of multiple cornoid lamellae (CL) within a benign epidermal acanthoma. Despite the presence of CL, which is a hallmark of the various clinical forms of porokeratosis (PK), the relationship between PKM and the classical types of PK is unknown, although both conditions coexisted in one patient.…”