Abstract: The early lesions of mycosis fungoides (MF) often present as non-specific eczematous changes, which are clinically difficult to distinguish from atopic dermatitis (AD). We report a case of MF patient who was misdiagnosed as atopic dermatitis in another hospital and experienced disease exacerbation after treatment with dupilumab. After discontinuing the biological agent and NB-UVB, the patient's condition improved. This case suggests that for elderly patients diagnosed as suspected AD, if there are clinical warning features indicating the possibility of MF, routine multi-point and repeated skin tissue pathological examinations with local drug withdrawal for 2 weeks should be performed, so as to avoid disease progression caused by misdiagnosis.

Key words: mycosis fungoides, dupilumab, cutaneous T-cell lymphoma, lymphoid reactions