An uncommon diagnosis for a recurrent erythematous patch in a paediatric patient.

A 14-year-old girl presented with a circular erythematous patch over the left buttock for approximately 10 years, with ongoing ulceration and papules developing over the last 4 years. Punch biopsies were taken within and above the patch for diagnosis. Both revealed marked inflammatory infiltrates with atypical, irregular lymphocytes and increased mitosis. Immunostaining revealed CD8 positivity and a pan T helper cell phenotype. T cell receptor gene rearrangement analysis showed T cell clonality in both biopsies. These findings were consistent with mycosisfungoides and associated lymphomatoid papulosis. Both are rare conditions but have been associated in 5%-20% of cases. A definitive association has not yet been established; however, T cell monoclonality shows 50%-60% share a common origin. Management options are extensive with no one treatment showing superiority. Our patient received low-dose radiotherapy with good outcomes, but subsequently required further radiotherapy. © BMJ Publishing Group Ltd (unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.