Ki-1 positive extranodal NK/T cell lymphoma, nasal type, mistaken as dermatomyositis - A case report and literature review

We report a case of a 38-year-old male with extranodal NK/T-cell lymphoma, nasal type, showing unusual clinical and pathological features. The patient was admitted for soft tissue swelling and tenderness in both legs. The patient had been treated intermittently 8 months prior for repeated muco-cutaneous ulcers. A muscle biopsy showed medium-sized atypical lymphoid cells with bizarre nuclei and plump cytoplasm, infiltrating to the skeletal muscle fibers with angiocentricity. The immunoresults were Ki-1+, CD56+, cytoplasmic CD3+, with EBV-in situ hybridization +. The patient rapidly deteriorated and died of sepsis and respiratory failure shortly after initiation of low-dose chemotherapy. A careful review of previous biopsies revealed scarce atypical lymphoid cells around vessels with similar immunoprofiles without the presence of Ki-1 positive cells. This case emphasizes that an extranodal NK/T-cell lymphoma may have a dermatomyositis-like diffuse presentation. Ki-1 co-expression can be an unexpected event in a process of the disease course; however, this should be validated with future studies.