CPC09 New-onset agminated Spitz naevi following hypopigmented pityriasis lichenoides chronica

Abstract

Abstract A 9-year-old girl presented to dermatology with erythematous scaly patches affecting her legs and arms, and hypo­pigmented patches affecting the trunk. She was otherwise fit and well, with no preceding illness or new medications. Treatment with mometasone 0.1% and an emollient was unsuccessful. Two years later, she had continued to develop new hypopigmented patches, as well as dark clustered naevi on the trunk. An incisional biopsy was taken from a hypopigmented patch of the right abdomen and one of the new naevi from the right hip. Incisional biopsy of the hypo­pigmented patch showed scattered necrotic keratinocytes in the epidermis with mild hydropic degeneration of basal cells and a mild superficial and perivascular lymphohistiocytic infiltrate in the dermis, consistent with pityriasis lichenoides chronica (PLC). Incisional biopsy of an eruptive naevus showed a junctional proliferation of melanocytes with overlying epidermal hyperplasia and hyperkeratosis and transepidermal elimination of melanin. Nests of epithelioid melanocytes were present at the rete tips, with no pagetoid spread and no atypia, consistent with an eruptive Spitz naevus. PLC is a benign lymphoproliferative disorder, typically presenting with erythematous scaly papules that relapse and remit. However, cases of PLC presenting with hypopigmentation alone have also been reported, as in this case, which can be part of a postinflammatory dyspigmentation or active disease (Elbendary A, Abdel-Halim MR, Youssef R et al. Hypopigmented lesions in pityriasis lichenoides chronica patients: are they only post-inflammatory hypopigmentation? Aust J Dermatol 2021; 63:68–73). The clustered pattern of Spitz naevi in this patient is termed agminated Spitz naevus. Eruptive disseminated and agminated Spitz naevi are much rarer than the solitary presentation. Triggers of eruptive Spitz naevi include pregnancy, blistering disorders and topical tacrolimus, and in one case following pityriasis lichenoides et varioliformis acuta (Mazzurco J, Menssen K, Schapiro B et al. Eruptive disseminated Spitz nevi in a 26-year-old African-American woman. Int J Dermatol 2012; 51:1270–1), while agminated Spitz naevi are reported to occur after radiotherapy and sunburn, and to arise in naevus spilus or congenitally hypo- or hyperpigmented patches. No cases of malignancy in agminated or eruptive disseminated Spitz naevi have been reported. In this case, the new onset of agminated Spitz naevi may have been triggered by the inflammatory process of PLC. As far as we can ascertain, there have not been previous cases of this published in the literature. Our patient’s hypopigmented areas have now started to self-resolve and we have planned for ongoing monitoring of the agminated Spitz naevi.