A 60-year-old man comes to the office after he was found to have a "low blood count" when attempting to donate blood. The patient is in his usual state of health and feels well. He has no chronic medical problems but has been treated for pneumonia twice during the past year. The patient takes no medications and does not use tobacco or alcohol. Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, and pulse is 76/min. Physical examination reveals mucosal pallor. There are no enlarged lymph nodes. The abdomen is soft and nontender. The spleen tip is palpable 5 cm below the left costal margin; the liver is normal in size. Stool guaiac is negative. Complete blood count results are as follows: Peripheral blood smear shows predominant lymphocytes with features as seen in the image below. Which of the following is the most likely diagnosis?

Question

A 60-year-old man comes to the office after he was found to have a "low blood count" when attempting to donate blood.  The patient is in his usual state of health and feels well.  He has no chronic medical problems but has been treated for pneumonia twice during the past year.  The patient takes no medications and does not use tobacco or alcohol.  Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, and pulse is 76/min.  Physical examination reveals mucosal pallor.  There are no enlarged lymph nodes.  The abdomen is soft and nontender.  The spleen tip is palpable 5 cm below the left costal margin; the liver is normal in size.  Stool guaiac is negative.  Complete blood count results are as follows:  Peripheral blood smear shows predominant lymphocytes with features as seen in the image below.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d416_97a7_bc81_e9a6417b2dcd_MD0003_00 This patient with 2 recent episodes of pneumonia has splenomegaly, anemia, thrombocytopenia, mild leukocytosis, and peripheral blood smear evidence of a leukocyte with "hairy" cytoplasmic projections suggesting the diagnosis of hairy cell leukemia. Hairy cell leukemia is a chronic B-cell malignancy that occurs primarily in people age >50. Manifestations arise due to the neoplastic infiltration of the bone marrow, spleen, and peripheral blood as follows: Bone marrow infiltration - causes bone marrow fibrosis with cytopenias. This may lead to recurrent infections (granulocytopenia), bleeding/bruising (thrombocytopenia), or fatigue/weakness (anemia). Splenic infiltration - causes splenomegaly. Mass effect may lead to symptoms of abdominal fullness or early satiety (gastric compression). Peripheral blood infiltration - peripheral blood smear shows abnormal circulating lymphocytes with "hairy" cytoplasmic projections. Although most patients are leukopenic due to bone marrow infiltration, a minority (such as this patient) have mild leukocytosis due to increased circulating lymphocytes. Hairy cell leukemia does not typically cause hepatomegaly, lymphadenopathy, or B symptoms. Diagnosis requires bone marrow biopsy with flow cytometry. (Choice A) Acute lymphoblastic leukemia is seen primarily in children (not adults) and usually manifests with symptoms related to neutropenia, anemia, or thrombocytopenia. Lymphadenopathy is common, and peripheral blood smear typically shows lymphoblasts (small cells, scant cytoplasm), not lymphocytes with "hairy" projections. lymphoblasts (Choice B) Chronic lymphocytic leukemia is usually characterized by significant leukocytosis (often >100,000/mm³), lymphadenopathy and B symptoms (unlike this patient). Peripheral smear typically shows "smudge cells". ³ "smudge cells" (Choice C) Gaucher disease is a lysosomal storage disease that may manifest with massive splenomegaly and cytopenias. However, hepatomegaly is universal and a "hairy" leukocyte would not be seen on peripheral smear. (Choice E) Hodgkin lymphoma is a B-cell neoplasm with characteristic Reed-Sternberg cells that usually manifests with a mediastinal mass or a painless, enlarged lymph node (often cervical). Reed-Sternberg cells (Choice F) Infectious mononucleosis may be associated with splenomegaly and atypical lymphocytosis. However, patients tend to be young and have the classic triad of fever, tonsillar pharyngitis, and lymphadenopathy (unlike this patient). (Choice G) Myelodysplastic syndrome is a malignant stem cell disorder that may cause anemia, leukopenia, and/or thrombocytopenia. Splenomegaly and leukocytosis are not typical features of myelodysplastic syndrome. Educational objective: Hairy cell leukemia is a chronic B-cell neoplasm that infiltrates the bone marrow, spleen, and peripheral blood, resulting in cytopenias, splenomegaly, and peripheral smear evidence of atypical lymphocytes with "hairy" cytoplasmic projections. Hepatomegaly, lymphadenopathy, and B symptoms are uncommon. Diagnosis is made with bone marrow biopsy.

A 60-Year-Old Man Comes to the Office After He Was