Case Presentation: A 45-year-old female with no significant medical history presented to the ED with three days of sharp epigastric pain radiating to the right lower quadrant associated with fever, chills, and multiple episodes of non-bilious, non-bloody emesis. She denied chest pain, shortness of breath, or bruising. Physical examination revealed normal vital signs except a temperature of 102.3° F. Abdominal examination revealed distension with right upper and lower quadrant tenderness without rebound; bowel sounds were hyperactive and there was no organomegaly. Remainder of the examination was unremarkable. Laboratory studies revealed a WBC 0.58 x 103/L, hemoglobin 7.5 g/dL, MCV 104.3 fl, RBC 2.32 mil/ul, and platelets 34 x 103/Lkul; WBC differential noted 9% neutrophils and 73% lymphocytes, of which 13% were atypical. Further laboratory studies demonstrated PT 14.3s, APTT 27.3s, and INR 1.4. A CT abdomen and pelvis with contrast showed wall thickening of the terminal ileum, cecum, and ascending colon; mesenteric fat stranding; and an abnormal air collection in the terminal ileum concerning for focal ischemia and/or perforation. Also noted were splenomegaly and abdominal adenopathy. The patient underwent an open right hemicolectomy. Throughout the hospitalization, her pancytopenia remained, despite filgrastim, antibiotics, and a total of 10 units of platelets and 4units of PRBC. Flow cytometry revealed monoclonal B-cells expressing CD19, CD20, CD22, CD23, CD10, and CD11c, as well as neutropenia with evidence of left-shifted maturation without blasts. Results favored low-grade follicular lymphoma and suggested hairy cell leukemia (HCL). Bone marrow biopsy noted a mutation in BRAF V600E which confirmed HCL. The patient received treatment with cladribine and rituximab. After two cycles of treatment, her bone marrow began to recover. The remainder of her hospitalization was uncomplicated and she was discharged with oncology follow-up.

Discussion: Hairy cell leukemia (HCL) is a rare chronic B-cell malignancy involving the bone marrow, peripheral blood, and the spleen. HCL is a lymphoproliferation of mature B cells- expressing CD 19, CD 20 CD 22, CD25, CD11c, and CD103. Classic HCL involves pathogenesis in the RAS-RAF-MAKP signaling pathway and a BRAF VF600E mutation leading to amplified cellular proliferation and malignancy. HCL is diagnosed in approximately 700 patients a year in the United States and accounts for 2% of all lymphoid leukemias. The median age of diagnosis is 55 and favors males. Patients present with nonspecific symptoms such as weakness, fatigue, and abdominal discomfort. The diagnosis is made by peripheral blood smear with flow cytometry and bone marrow biopsy. The characteristic cells are large with circumferential, hair-like cytoplasmic projections and a well-defined nucleus. Treatment is based on risk assessment. Currently, cladribine is used for HCL in patients with no concomitant infection. Rituximab may be incorporated as well. HCL is incurable; however, without treatment, median survival is approximately four years. With treatment, survival rates are only marginally lower than the general population.

Conclusions: Physicians should keep HCL in the differential diagnosis for a young patient who presents with nonspecific abdominal discomfort and pancytopenia