Extramedullary Relapse of Acute Promyelocytic Leukaemia (APL) at an Unusual Site (External Auditory Canal)

A 55-year-old lady diagnosed with APL-M3 variant in 2021 and treated with AIDA regimen to complete remission (CR1) and negative MRD. She maintained MRD negative results at 3 months post treatment.

Six months after treatment, she presented with persistent feeling of blocked right ear canal and otalgia. She had an inflamed right ear canal and difficulties to visualise the right tympanic membrane due to a polypoidal lesion. She did not respond to initial antibiotic treatment and had progressed to decreased auditory acuity with persistent ear pain and development of right cervical and periauricular lymphadenopathy.

Her blood counts were within normal range at this time. MRI head demonstrated in FLAIR coronal (Figure 1A) and T2 axial (Figure 1B) images, a soft tissue in right external auditory canal. The biopsy of this mass showed monomorphic cells with high nucleocytoplasmic ratio. On immunohistochemistry, these were positive for CD117(C), MPO (D), CD33 and CD68. A contemporaneous bone marrow biopsy was in morphological remission, however the flowcytometry found a population of CD33, CD117 and MPO positive cells and positive MRD of 18.5%. Cytogenetics (E) showed ongoing presence of the t (15, 17). She had a lumbar puncture and flowcytometry results of CSF analysis ruled out CNS involvement.

She commenced arsenic and ATRA treatment and achieved PET and bone marrow remission post induction. She continued with 3 further consolidation cycles, followed by consolidation with an autologous stem cell transplant and at D+100 continues to be MRD negative in bone marrow and radiological remission on PET.

This is an unusual extramedullary relapse of APL (external auditory canal), while the blood counts were normal and bone marrow was in morphological remission. This reiterates the importance of MRD monitoring and low threshold to investigate unusual or persistent auditory symptoms, as these may be the first presentation of relapse of the disease. Extramedullary relapse is infrequent in APL and relapse in auditory canal has been reported as an unusual site of relapse [1, 2], considering that usually the extramedullary relapses happen in skin or CNS.

The authors declare no conflicts of interest.