A 20-year-old woman comes to the emergency department due to bloody stools. Approximately an hour ago, the patient had a bowel movement that appeared grossly bloody. For the past month, she has also had decreased energy. Temperature is 37 C (98.6 F), blood pressure is 110/60 mm Hg, pulse is 110/min, and respirations are 20/min. The patient appears tired. Cardiopulmonary examination reveals mild tachycardia. The abdomen is soft without organomegaly. Skin examination shows pallor and scattered bruises in various stages of healing throughout the trunk. Complete blood count results are as follows: Which of the following is the most likely cause of this patient's condition?

Question

A 20-year-old woman comes to the emergency department due to bloody stools.  Approximately an hour ago, the patient had a bowel movement that appeared grossly bloody.  For the past month, she has also had decreased energy.  Temperature is 37 C (98.6 F), blood pressure is 110/60 mm Hg, pulse is 110/min, and respirations are 20/min.  The patient appears tired.  Cardiopulmonary examination reveals mild tachycardia.  The abdomen is soft without organomegaly.  Skin examination shows pallor and scattered bruises in various stages of healing throughout the trunk.  Complete blood count results are as follows:  Which of the following is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

11ec160b_3970_3941_9249_3dfd43ed778b_MD0001_00 This patient has gastrointestinal bleeding and ecchymosis secondary to thrombocytopenia; although anemia (eg, pallor) would be expected with significant bleeding, her low leukocyte count indicates pancytopenia, which is generally caused by one of the following: Bone marrow aplasia: Hematopoietic stem cells in the bone marrow are unable to proliferate and differentiate into mature blood cells due to aplastic anemia, nutritional impairment, infection (eg, parvovirus, HIV), or cytotoxic medications. Bone marrow infiltration: Cancer, fibrosis, or infection (eg, tuberculosis) fills the bone marrow and crowds out hematologic cells, thereby preventing blood cell replication and maturation. Mature blood cell destruction: Circulating mature blood cells may be destroyed due to disseminated intravascular coagulation or thrombotic thrombocytopenic purpura; extravascular mature blood cells may be destroyed or sequestered in the spleen due to hypersplenism. Based on this patient's laboratory and physical examination results, several answer choices can be eliminated. The presence of a normal MCV makes vitamin B₁₂ or folate deficiency unlikely because these are associated with macrocytic (not normocytic) anemia (Choice E). Hypersplenism is also unlikely because abdominal examination would show significant splenomegaly (Choice C). Chronic myelogenous leukemia, an infiltrative cancer associated with constitutively active tyrosine kinase, is also unlikely because this condition is usually associated with dramatic leukocytosis (not leukopenia) (Choice B). Therefore, the most likely cause of this patient's pancytopenia is aplastic anemia (AA). Although AA is linked to certain medications, infections, toxins, or radiation, most cases are idiopathic and thought to be caused by autoimmune-induced loss of multipotent hematologic stem cells. In idiopathic AA, an underlying insult (eg, mutation, virus) causes alteration of surface antigens on multipotent stem cells, making them appear foreign and triggering a cytotoxic T-cell response. Cytokines released by T-helper cells (type 1 cytokines) also contribute to the pathogenesis, most notably interferon-gamma, which triggers apoptotic cell death due to the stimulation of a destructive cytokine cascade and the increased expression of the Fas receptor on the hematologic stem cell surface. (Choice D) Autoantibodies against glycoprotein IIb/IIIa cause immune thrombocytopenia, which is marked by thrombocytopenia and no change in the other cell lines. Educational objective: Aplastic anemia is a form of bone marrow failure in which patients have decreased production of all cell lines (platelets, erythrocytes, and leukocytes). It is primarily caused by the autoimmune destruction of multipotent hematologic stem cells due to an alteration in their surface antigens, leading to a cytotoxic T-cell response and release of interferon-gamma from T-helper cells (triggers apoptotic cell death).

A 20-Year-Old Woman Comes to the Emergency Department Due to Bloody