Behçet’s disease（BD） is a multi organ involvement, recurrent syndrome with vasculitis as the underlying histopathological lesion. We report a case of a 39-year-old man who presented with a diagnostic dilemma simulating Behcet's disease. Invalid antirheumatic treatment raising the suspicion of a malignant neoplasm. The bone marrow pathologic examination revealed flower-like atypical lymphocytes. Finally, the diagnosis of adult T cell leukemia clinically could be made when recognized the hallmarks laboratory examination. The concurrent presentation of these two entities seems to be more than extremely rare

A 35-year-old chinese man，presented with complaints of oral ulceration for 2 years. (usually 1–2 aphthae healing within 10 days) recurrent up to 6–7 times per year, occasional red papules on both upper arms, not taking any regular medications. He developed genital ulcers, diarrhea and had intermittent low-grade fever of 38°C for the past 2 weeks, associated with night sweats, and expressed loss of weight was observed. Ophthalmologic examination was normal. The patient was admitted to Rheumatology division, where, based on international classification criteria(ICBD 2014) , Behçet’s disease was be considered.

At admission, his body temperature was 38.3°C , blood pressure was 125/75 mmHg and heart rate 85 and regular respiration. The cardiopulmonary examination was normal, no tenderness in abdomen. A ulcer about 1 cm x 0.5 cm in size could be seen on the right side of the tongue tip (Fig. 1), and an ulcer about 1.5 cm x 0.7 cm in size could be seen on the foreskin of the glans (Fig. 2). Acupuncture test was positive.

Blood tests showed leukocytosis up to 27.01 × 109/L (normal range: 3.5–9.5 × 109/L), The lactate dehydrogenase level was 530 IU/l (normal range: 109–245 IU/l), and he had elevated serum ionized calcium (3.76 mmol/L; normal range: 2.10–2.25 mmol/L). The autoantibody spectrum was negative. Colonoscopy: Sigmoid colon occasionally has ulcers of about 0.5 cm x 0.5 cm in size (Fig. 3). X-ray computed tomography (CT) was performed for abdomen regions. The scanner revealed several lymph node chains in retroperitoneum and mesentery. 

In these situations, further investigation of such cases is needed to clarify the pathogenesis of ATL simulating BD. In summary, ALT can mimic the clinical features of BD. It should be proposed for those ”BD”patients with poor response to routine therapy, it is necessary to take into account other system diseases, and also should not be excluded imprudently as hematological malignancies．