Hematology & oncology Clinical Case / MCQS / Uworld for Usmle step 2 / case 4 with answer and explanation and references and Educational objective
A
44-year-old-man comes to the emergency department due to fever and cough. The patient
reports progressive fatigue and dyspnea on exertion over the past several weeks
to the point that he was unable to mow the lawn last weekend. He started having
fever, chills, and productive cough yesterday. The patient has no prior medical
problems and takes no medications. He does not use tobacco, alcohol, or illicit
drugs. Temperature is 38.8 C (102 F), blood pressure is 100/60 mm Hg, pulse is
110/min, and respirations are 24/min. Physical examination shows mucosal pallor
and scattered ecchymoses. Lung auscultation reveals left-sided crackles and
bronchial breath sounds. There is no lymphadenopathy or splenomegaly.
Laboratory results are as follows :
Complete blood count
Hemoglobin 6 g/dL
Mean corpuscular
volume 98 µ
Reticulocytes 0.3%
Platelets 17,000/m
Leukocytes 2,000/m
Serum chemistry
Creatinine 0.8 mg/dL
Calcium 8.8
mg/dL
Coagulation studies
INR 1.0
(normal 0.8-1.2)
Activated PTT 23 sec
Lactate dehydrogenase, serum 85 U/L
Left
lower lobe consolidation is seen on chest x-ray. Peripheral blood smear reveals
decreased leukocytes and platelets but is otherwise unremarkable. Which of the following
is the most likely mechanism of this patient's hematologic abnormalities?
|
A. Acquired
deficiency of pluripotent stem cells. B. Excessive
collagen deposition in the bone marrow . C. Impaired
DNA synthesis in precursor cells . D. Malignant
proliferation of mature lymphocytes . E. Replacement
of bone marrow by plasma cells . |
Answer : A
Explanation:
|
Aplastic anemia |
|
|
Pathogenesis |
Bone marrow failure due to hematopoietic stem cell deficiency (CD34+) |
|
Causes |
•
Autoimmune •
Infections (eg, parvovirus B19, Epstein-Barr virus) •
Drugs (eg, carbamazepine, chloramphenicol,
sulfonamides) •
Exposure to radiation or toxins (eg, benzene,
solvents) |
|
Clinical findings |
Symptoms result from pancytopenia: •
Anemia (fatigue, weakness, pallor) •
Thrombocytopenia (mucosal bleeding, easy
bruising, petechiae) •
Leukopenia (recurrent infections) |
|
Diagnosis |
Biopsy showing hypocellular bone marrow composed mainly of fat &
stromal cells |
This
patient most likely has aplastic anemia as he has pancytopenia (decrease in all
3 blood cell lineages) with no splenomegaly and no abnormal cells on peripheral
smear. Aplastic anemia is an acquired deficiency or absence of pluripotent stem
cells. It is associated with exposures (eg, drugs, toxins, radiation), viral
infections (eg, parvovirus 819, HIV, Epstein-Barr virus), and autoimmune
conditions (eg, lupus, eosinophilic fasciitis). Direct damage to and autoimmune
targeting of stem cells are 2 potential mechanisms that result in aplasia.
Patients
manifest the following sequelae of pancytopenia :
• Anemia (eg, severe fatigue, pallor)
• Leukopenia (eg, infections such as
pneumonia)
• Thrombocytopenia (eg, mucocutaneous
bleeding)
The
complete blood count and peripheral smear are notable for pancytopenia and inadequate
erythropoiesis demonstrated by a low reticulocyte count; however, the cells are
all morphologically normal and the anemia is usually normocytic. A definitive diagnosis
is made by bone marrow biopsy demonstrating hypocellular marrow with a few
normal hematopoietic cells, no myeloid infiltration or fibrosis, and
predominantly stroma and adipocytes.
(Choice
B) Myelofibrosis, characterized by collagen or reticulin deposition in the bone
marrow, presents with fatigue, fevers, and hepatosplenomegaly from extramedullary
hematopoiesis. Peripheral blood cell counts may be either elevated or
decreased.
(Choice
C) Impaired DNA synthesis in precursor cells can result from nutrient deficiencies
(eg, 8,, folate) and antimetabolite drugs (eg, azathioprine, methotrexate).
However,
this leads to a megaloblastic anemia (mean corpuscular volume >100 1.1m')
with macrocytic erythrocytes, mild thrombocytopenia, and multilobed neutrophils
on peripheral smear.
(ChoiceD
) Malignant proliferation of mature lymphocytes is seen in chronic lymphocytic leukemia
(CLL) and hairy cell leukemia (HCL). Both present with bleeding, anemia, fevers,
and splenomegaly. On peripheral smear, HCL has lymphocytes with hairy projections
and CLL has smudge cells and numerous mature lymphocytes.
(Choice
E) Replacement of bone marrow by plasma cells is seen in multiple myeloma, which,
unlike in this patient, usually manifests with hypercalcemia, anemia, renal
disease, and lytic bone lesions.
Educational
objective:
Aplastic
anemia is an acquired deficiency of pluripotent stem cells that can result from
certain exposures, viral infections, or autoimmune conditions. The
manifestations, including fatigue, infection, and mucocutaneous bleeding, are
due to pancytopenia. Cellular morphology is normal and splenomegaly is absent.
|
References: 1. How I treat acquired aplastic anemia. New
link : |
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