Detecting T‐cell receptor clonality in patients with severe atopic dermatitis refractory to dupilumab

Abstract Background Trials and real‐life studies demonstrated clinically meaningful improvements of disease activity in the majority of patients with moderate to severe atopic dermatitis (AD) treated with the anti‐IL‐4RA‐antibody dupilumab. However, misdiagnosis or confounding skin diseases in particular cutaneous T‐cell lymphoma (CTCL) may lead to inadequate response. Objective To investigate the clinical and pathological features of patients with AD who showed insufficient response to dupilumab. Methods We reviewed the medical records of 371 patients treated with dupilumab for severe AD. Insufficient response was defined as failure to achieve an improvement of the eczema area severity index (EASI) of at least 50% (EASI‐50) at Week 16 and of 75% (EASI‐75) at Week 52. Among 46 patients with insufficient response, 35 patients consented to a re‐evaluation including a full physical exam, biopsies and laboratory assessments including immunohistochemistry and T‐cell receptor gene rearrangement analysis to differentiate CTCL. Results Of the 371 patients treated with dupilumab, 46 (12.3%) patients showed insufficient response to dupilumab. Of these, 35 underwent further evaluation, and 19 (54.2% of inadequate responders) were finally diagnosed with mycosis fungoides (MF). In these patients, transition to or addition of conventional MF treatment led to clinical improvements. Conclusions Insufficient response to dupilumab treatment may help uncover early MF on an existing AD background.