Hematology · Bone Marrow Failure Syndromes
The facts most likely to be tested
Aplastic anemia is characterized by pancytopenia with a hypocellular bone marrow replaced by fatty infiltration.
The gold standard for diagnosis is a bone marrow biopsy showing a hypocellular marrow without evidence of malignancy or fibrosis.
Patients present with symptoms of pancytopenia, including fatigue (anemia), mucocutaneous bleeding (thrombocytopenia), and recurrent infections (neutropenia).
Physical examination is notable for the absence of hepatosplenomegaly and lymphadenopathy, which helps distinguish it from leukemia or lymphoma.
The pathophysiology involves T-cell mediated autoimmune destruction of hematopoietic stem cells.
First-line treatment for young patients with a matched sibling donor is allogeneic hematopoietic stem cell transplantation.
Patients who are not candidates for transplant are treated with immunosuppressive therapy using anti-thymocyte globulin (ATG) and cyclosporine.
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A 22-year-old male presents to the clinic with a two-week history of worsening fatigue, easy bruising, and a low-grade fever. Physical examination reveals petechiae on the lower extremities and pallor, but there is a notable absence of hepatosplenomegaly or lymphadenopathy. Laboratory studies demonstrate a hemoglobin of 7.2 g/dL, a platelet count of 18,000/µL, and an absolute neutrophil count of 450/µL. A peripheral blood smear shows normocytic, normochromic red blood cells with no abnormal circulating blasts.
What is the most appropriate next step in the management of this patient?
Bone marrow biopsy
The patient presents with classic signs of pancytopenia without organomegaly, necessitating a bone marrow biopsy to confirm the diagnosis of aplastic anemia by demonstrating a hypocellular marrow.
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Etiology / Epidemiology
Characterized by bone marrow failure due to hematopoietic stem cell destruction. Often idiopathic or secondary to toxic exposures.
Clinical Manifestations
Presents with pancytopenia leading to fatigue, bleeding, and infection. Pancytopenia without splenomegaly is the classic hallmark.
Diagnosis
Bone marrow biopsy showing hypocellular marrow (<25% cellularity) is the gold standard.
Treatment
Allogeneic hematopoietic stem cell transplantation is curative for young patients. Antithymocyte globulin (ATG) plus cyclosporine is first-line for others.
Prognosis
High mortality if untreated. Clonal evolution to myelodysplastic syndrome or paroxysmal nocturnal hemoglobinuria is a major risk.
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Epidemiology & Etiology
Most cases are idiopathic (immune-mediated). Secondary causes include radiation, chemotherapy, and exposure to toxins like benzene. Medications such as chloramphenicol, sulfonamides, and carbamazepine are classic triggers. Viral triggers include hepatitis and Epstein-Barr virus.
Pertinent Anatomy
The disease involves the bone marrow stroma and hematopoietic stem cells. The marrow becomes replaced by fatty tissue, resulting in a profound reduction in all three cell lines.
Pathophysiology
T-cell mediated autoimmune destruction of hematopoietic stem cells is the primary mechanism. This leads to a failure of hematopoiesis, resulting in pancytopenia. The lack of compensatory marrow hyperplasia distinguishes this from peripheral destruction syndromes.
Clinical Manifestations
Patients present with anemia (fatigue, pallor), thrombocytopenia (petechiae, ecchymosis, mucosal bleeding), and neutropenia (recurrent infections). Fever in the setting of neutropenia is a medical emergency. A key physical exam finding is the absence of hepatosplenomegaly or lymphadenopathy, which helps rule out malignancy.
Diagnosis
The bone marrow biopsy is the gold standard, revealing a hypocellular marrow with <25% cellularity replaced by fat. Peripheral blood counts show pancytopenia with a low reticulocyte count. Flow cytometry is required to rule out paroxysmal nocturnal hemoglobinuria (PNH) clones.
Treatment
For patients <40 years with a matched sibling donor, allogeneic hematopoietic stem cell transplantation is the treatment of choice. For those ineligible for transplant, antithymocyte globulin (ATG) combined with cyclosporine is the standard immunosuppressive regimen. Avoid unnecessary blood transfusions to prevent alloimmunization prior to transplant.
Prognosis
Untreated severe disease has a high mortality rate due to sepsis or intracranial hemorrhage. Long-term survivors face a significant risk of clonal evolution into myelodysplastic syndrome or acute myeloid leukemia.
Differential Diagnosis
Myelodysplastic syndrome: usually shows hypercellular marrow with dysplasia
Paroxysmal nocturnal hemoglobinuria: presence of hemolysis and CD55/CD59 deficiency
Fanconi anemia: associated with congenital anomalies and DNA repair defects
Hairy cell leukemia: presents with massive splenomegaly and pancytopenia
Acute leukemia: marrow is typically hypercellular with blasts