DP08 Paediatric-onset lymphomatoid papulosis (LyP) in a 2 year old: a case report exploring the diagnostic difficulty of LyP in children

Abstract Lymphomatoid papulosis (LyP) is a rare primary cutaneous CD30+ T-cell lymphoproliferative disorder. Clinically it is characterized by recurrent erythematous skin nodules occurring at any body site, more commonly on the extremities [Blanchard M, Morren MA, Busschots AM et al. Paediatric-onset lymphomatoid papulosis: results of a multicentre retrospective cohort study on behalf of the EORTC Cutaneous Lymphoma Tumours Group (CLTG). Br J Dermatol 2024; 191: 233–42]. The aetiology is unknown, and hypothesized theories implicate the role of viral illnesses including human T-cell lymphotropic virus 1, herpes simplex virus and endogenous viruses. The peak of incidence is between the fourth and fifth decades, with a slight male predilection. LyP is extremely rare, with an estimated 0.1 to 0.3 cases per 1 million person-years in the paediatric population. However, it accounts for one of the two most common paediatric cutaneous lymphoproliferative disorders alongside mycosis fungoides. LyP provides a diagnostic challenge and requires clinicopathological correlation to avoid misdiagnosis. LyP may mimic many other conditions both benign and malignant. We identified a case of LyP in a 2-year-old boy, which explores the use of close clinicopathological correlation for diagnosis. Initial presentation revealed a nonpruritic papular rash beginning at 8 months old with scattered 2–4-mm papules distributed at the flexures, face and groin. There was evidence of scarring areas where papules had spontaneously resolved. There was no hepatosplenomegaly noted on examination. The patient was otherwise systemically well, meeting developmental milestones. His past medical history included being born preterm at 32 weeks’ + 6 days’ gestation, with a 19-day stay in the neonatal intensive care unit due to respiratory distress syndrome, neonatal hypoglycaemia and jaundice, treated with phototherapy. There was no significant family history. Initial differential diagnoses included pityriasis lichenoides et varioliformis acuta; however, the condition was resistant to topical corticosteroids and oral antibiotics. Two incisional biopsies were arranged, which confirmed a combination of type B and type E LyP. As the rash is widespread, troublesome and causing scarring, the plan is to commence methotrexate; this was delayed as he required chickenpox vaccination prior to commencing. Histologically, LyP is divided into five main subtypes (A to E) recognized by the World Health Organization and European Organisation for Research and Treatment of Cancer. This subdivision has not been clearly linked to disease prognosis and has no implications in management. While topical corticosteroids are the most common treatment adopted, other options include watchful waiting, phototherapy and systemic methotrexate. LyP is associated with increased risk of haematological malignancy, with mycosis fungoides and anaplastic large cell lymphoma being the most common. Clinicians should remain vigilant in diagnosing LyP. Although its course is often benign, the association with haematological malignancy requires both careful clinicopathological correlation for diagnosis and long-term follow-up.