This case evaluates follicular psoriasis, an uncommon variant manifesting as scaly folliculocentric
hyperkeratotic eruptions of the trunk and extremities.
Psoriasis is a common autoimmune dermatosis representing an interplay between certain genetic predisposing factors along with clonally restricted Th1 T cells responding to epidermal keratinocyte derived antigen. A unique IL-17/IL-23 cytokine rich milieu is pathogenetically significant and conducive to its salient histomorphologic features, such as epideram hyperplasia and intraepidermal influx of neutrophils. Many of the effector intraepidermal lymphocytes are of the CD8 subset; myeloid dendritic cells are also key players in the evolution of psoriasis.1
The worldwide prevalence of psoriasis depends on age and geographic location. In the United States, the incidence of psoriasis is approximately 2%, with a higher frequency in the Caucasian population.2 The classic cutaneous manifestation is that of plaque psoriasis also referred to as psoriasis vulgaris. Characteristic lesions are described as elevated well-circumscribed erythematous plaques covered by silvery scales that exhibit the Auspitz sign upon removal.
Follicular psoriasis (FP) is an uncommon variant manifesting as a scaly folliculocentric hyperkeratotic eruptions of the trunk and extremities, irrespective of the presence or absence of conventional lesions of psoriasis vulgaris.
The incidence of FP is unknown with roughly 23 reported cases emphasizing its rarity given the overall incidence of conventional psoriasis in the general population. Due to the lack of awareness, the clinical presentation is often misdiagnosed as other follicular dermatoses, including bacterial folliculitis, pityriasis rubra pilaris, keratosis pilaris, or follicular eczema.
A 61-year-old white woman presented with a sudden and self-remitting pruritic papular rash of the bilateral forearms and bilateral lower legs of several months’ duration. She denied any constitutional symptoms. The patient had no known history of kidney, liver, thyroid, or hematologic diseases. Other family members did not have a similar eruption.
Physical examination revealed numerous erythematous crusted papules that extended to the superior and inferior back (Figures 1A-D). Symptomatic palliation was seen with the use of a pimecrolimus cream (Elidel).
Multiple shave biopsies were performed on the right superior back, right inferior back, right upper arm, and right forearm. Light microscopic examination revealed an extensive pustular folliculocentric process. There was permeation of the outer root sheath epithelium by neutrophils. In addition, the ostium of the follicle was occluded by keratin intimately admixed with neutrophils (Figures 2A and B).
The background epidermis exhibited classic features of a psoriasiform diathesis, the hallmarks being those of neutrophil-imbued parakeratosis, granular cell layer loss and dilated dermal papillae capillaries lying in intimate apposition to the basal layer of the epidermis (Figures 2C and D). Direct immunofluorescence revealed entrapment of immunoglobulin and complement within the stratum corneum along with variable granular deposition of complement along the dermal epidermal junction.
A diagnosis of FP was made. The patient was placed on a tumor necrosis factor inhibitor that resulted in regression of the eruption. It was subsequently established that the patient had a remote history of psoriasis.
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