BI21 Intermittent and progressive pustular psoriasis during chemotherapy cycles in a toddler

Abstract An 18-month-old with high-risk stage IV neuroblastoma was referred for the difficult evaluation of an intermittent and evolving rash. He presented with erythematous, pruritic papules on his chest, under his portal catheter dressing. After a change of dressing type, this progressed, with a pustular, pruritic eruption across his scalp. Differential diagnoses included eosinophilic folliculitis, contact dermatitis and transfusion reaction. Viral and bacterial swabs and an open application test to chlorhexidine were negative. Topical betamethasone valerate 0.1% gave improvement. Just before his next chemotherapy cycle (cisplatin and etoposide), the rash recurred as a pruritic pustular eruption across the frontal and retroauricular scalp; skin biopsy suggested nonspecific subacute eczematous dermatitis. A lack of eosinophils was suspicious, but blood counts showed absent circulating eosinophils. From December to April, the rash regularly improved after chemotherapy but then recurred and progressed as counts recovered prior to his next cycle. Differentials including Demodex, Pityrosporum, dermatitis with koebnerization and chemotherapy reactions such as neutrophilic eccrine hidradenitis were considered. Topical ivermectin and ketoconazole did not help. He had partial response to topical corticosteroids including clobetasol propionate 0.05%. A second biopsy was taken due to clinical suspicion of psoriasis, and 10 days of oral prednisolone was given to try to clear his skin for autologous stem cell transplantation (HSCT). Biopsy described acanthosis and elongated rete ridges, parakeratosis with neutrophils, and blood vessels extending into dermal papillae in keeping with psoriasis. Fortunately the condition improved substantially and he successfully underwent HSCT with granulocyte colony-stimulating factor (GCSF). For the following 2 months’ cycles, the rash did not recur, but after his second HSCT with GCSF it recurred and continued to spread as cell counts normalized. A few isolated face and scalp lesions quickly spread with pruritic erythematous papules. Many had scale, some had a collarette of scale, and some were pustular and some hyperpigmented. They were extensive over the back with less abdominal involvement. Herpes simplex virus and varicella zoster virus swabs, KOH scrapes and human herpesvirus-6 were negative. He was treated with topical calcipotriol and mometasone 0.1%, with consideration of acitretin should he not improve. Fortunately, the rash settled with topical therapy and time. After completing proton radiotherapy prior to tumour resection, he had six cycles of maintenance immunotherapy (dinutuximab) with no recurrence of the rash, despite monthly GCSF, and good cell counts, and has now completed his oncological therapy.