Pustular Psoriasis Occurring on the Striae Distensae: Isotopic Phenomenon/Koebner's Phenomenon.

Sir,

Occurrence of new skin disorder at the site of previously healed disease is called Wolf's isotopic phenomenon. Occurrence of lesions at the site of trauma is called Koebner's phenomenon. Herein, we report a unique presentation of pustular psoriasis involving the striae distensae.

A 23-year-old male patient reported to the dermatology clinic with complaints of recurrent episodes of generalized pustular eruptions since the age of 15 years. The crops of pustules were preceded or accompanied by fever and constitutional symptoms. The biopsy of the pustular lesion showed Munro's micro abscess and spongiform pustule of Kogoj, thus confirming the diagnosis of generalized pustular psoriasis.

His disease was relatively recalcitrant which required frequent administration of systemic steroids and cyclosporine during acute exacerbation. Thus, he developed steroid-induced striae over the anterior abdomen, arms, and thighs.

The current episode of generalized pustulation is characterized by the striking occurrence of pustular eruptions on the striae over anterior abdomen in the infraumbilical region, the flanks, arms, and thighs [Figures 1–3]. The initial crops of pustules in the striate were followed by pustular lesions elsewhere. The previous two episodes over the past 3 years (since the time the striae made its onset) were characterized by the involvement of striae by pustular eruptions initially followed by the occurrence of pustular lesions elsewhere in a generalized fashion. Thus, the predilection of the striae by the pustular eruptions is what is interesting and unique in this patient.

Figure 1

Pustules involving the striae on the anterior abdomen

Figure 3

Closer view of the pustules on the striae

Pustules involving the striae on the left flank

Striae distensae are linear smooth bands of atrophic dermis that at first are red, then purple, and finally white. There are several conditions which are reported to involve the striae, namely psoriasis, lichen planus, vitiligo, warts, molluscum contagiosum, urticarial vasculitis, leukemia cutis, pruritic urticarial papules and plaques of pregnancy, lupus erythematosus, chronic graft versus host disease, and keloids.[12]

The occurrence of the lesions of another disease on the striae distensae is described by some authors as Koebner's phenomenon, i.e., occurrence of the lesions (psoriasis) on the site of trauma (striae),[23] whereas the other school of authors describe this phenomenon as Wolf's isotopic phenomenon, i.e., occurrence of a new unrelated disease (psoriasis) at the site of previously healed disease (striae).[1] The current presentation can thus be explained as both Koebner's phenomenon as well as isotopic phenomenon.

The exact etiology for the predilection of pustular psoriasis to involve the striae is a mystery. The possible hypothesis put forth by Verma includes imperceptible micro-trauma to the epidermis during the process of striae formation, mast cell infiltration, increased CD4+ T-cells infiltration, increased dermal vascularity, and augmented local production of adhesion molecules.[4]

Thus, this case illustrates the rare and unique presentation of pustular psoriasis on the striae distensae.

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Conflicts of interest

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