LAUSR

Dear Editor, A 34-year-old woman complaining of a solitary pruritic lesion on her shin since 7 months was presented. She had no medical or drug history, with no other skin disease. On physical examination, a single round hyperkeratotic plaque with a yellowish white shell-like scale was observed. The lesion's scale was compact with special and interesting appearance: very thick, firmly adherent, with concentric pattern and the central part was slightly sunken with a sharp erythematous border on her shin (Figure 1). No sign of any problem was observed on other body parts and the nail examination was normal. Based on the physical examination due to the solitary state of the lesion, the differential diagnosis of Bowen's disease, keratoacanthoma, was suggested. A biopsy sample was taken. During biopsy sampling, the thick hyperkeratotic shell-like scale was separated as a shield with a sunken center and a biopsy sample was finally taken from the erythematous base of the lesion. Histopathologically, acanthosis, hypogranulosis, lymphomononuclear cells exocytosis with the red blood cells extravasation and scattered neutrophils without atypia were observed, all in favor of psoriasis disease (Figure 2). The patient was treated with the diagnosis of ostraceous psoriasis. Use of topical treatments (calcipotriol and semipotent corticosteroid creams) resulted in favorable improvement after a few weeks of follow-up. The three hyperkeratotic forms of psoriasis include the ostraceous, rupioid and elephantine morphological subtypes. Due to their rare incidence, to date, only a few case reports have been published. In ostraceous psoriasis, the lesions manifest as firmly adherent thick scales in various colors with a surface resembling an oyster shell. However, in the rupioid type, concentric, round, cylindrical hyperkeratotic areas are observed. In the elephantile form, large thick simple lesions with long-lasting (chronic) plaques are seen, more commonly on the dorsal side of the buttock and the upper extremities. Differentiation of the rupioid lesions and the ostraceous form is not easy and they are sometimes mistaken for each other. Previously, the term “exudative psoriasis” was used for both conditions. It was believed that the layers formed by serous fluid are responsible for the formation of the exudative crusts. The two types of ostraceous and rupioid psoriasis are mainly distinguished based on the clinical and pathological features, which are rarely helpful. Typical psoriasis pathological findings are the same for both types, including acanthosis along with elongation of interpapillary processes, hypo or agranulosis, hyper or parakeratosis, capillaries dilatation and perivascular infiltration of lymphocytes with or without neutrophils in the epidermis or stratum corneum; these evidences were also reported in our case. Ostraceous psoriasis drives the physician's attention toward the number of lesions, resistance to topical medications and their association with psoriatic arthritis. However, none of these three factors were observed in our patient. Contrary to the results of our study, most of the published case reports indicated resistance to topical treatments, possibly due to hyperkeratosis. On the other hand, some studies have stated that this condition responds to biologic and immunosuppressive drugs. In our case, after separation of the thick scale, single erythematous plaque was treated with topical calcipotriol and corticosteroids, resulting in complete recovery of the lesions. This patient presented with ostraceous psoriasis, which itself is a very rare type of a common disease and rarely responds to topical treatments, because of its thick scale, whereas contrary results were experienced in our patient. This indicates that limited and solitary lesions may respond better to topical therapies after lesion's scale separation.