Rationale:Acute promyelocytic leukaemia (APL) is a rare subtype of acute myelogenous leukaemia. With advances in treatment regimens, namely, introduction of all-trans-retinoicacid, outcomes have drastically improved, its side effects should not be ignored. Mycosis fungoides is one of the side effects of all-trans-retinoicacid treatment, but it may also be a clinical manifestation before disease progression. However, it rarely appears and is easily overlooked. This leads to being easily misled during the treatment process, affecting the treatment plan, and resulting in adverse consequences. Therefore, early identification and judgment can not only provide appropriate treatment options, but also prevent and treat further disease progression.Patient concerns:The patient was hospitalized for pancytopaenia. After completing the examination, the patient was finally diagnosed with acute promyelocytic leukaemia (acute myelogenous leukaemia-M3). We administered tretinoin and arsenous acid. Evaluation of the treatment effect on the 7th day after chemotherapy showed that the bone marrow morphology showed complete remission. After the second course of chemotherapy, the patient developed red miliary macular papules, which gradually worsened. After completing relevant inspections, Considering that the cases was complicated with skin mycosis fungoides, the patient was treated with budesonide ointment and methylprednisolone as chemotherapy.Diagnoses:Upon examination, the patient was initially diagnosed with acute promyelocytic leukaemia. Evaluation of the treatment effect on the 7th day after chemotherapy showed that the bone marrow morphology showed complete remission. After the second course of chemotherapy, we discovered the patient was diagnosed with skin mycosis fungoides.Interventions:Systemic chemotherapy is first given when a patient was diagnosed with acute promyelocytic leukaemia. After the patient happened skin mycosis fungoides, We have adjusted the treatment plan and supplemented it with other treatment plans based on the original chemotherapy, After 2 months of treatment, his condition gradually improved.Outcomes:All-trans-retinoicacid in the treatment of APL must be given attention because mycosis fungoides should not only be distinguished from infectious diseases but also be further assessed with regard to disease progression and metastasis.Lessons:Acute promyelocytic leukemia needs to be treated with arsenic trioxide. All-trans-retinoicacid in the treatment of APL must be given attention mycosis fungoides. Early diagnosis can guide accurate treatment, which is of great help in alleviating the pain of patients and improving the cure rate.
