Hematology & oncology Clinical Case / MCQS / Uworld for Usmle step 2 / case 2 with answer and explanation and references and Educational objective
A
5-year-old boy is brought to the emergency department for increasing fatigue.
He was well until 2 weeks ago when he had an upper respiratory infection from
which he has not recovered. He has had poor appetite and lost 1 kg (2.2 lb)
over the last 3 weeks. His past medical history is unremarkable. His
temperature is 39.4° C (103° F), blood pressure is 100/70 mm Hg, pulse is
134/min, and respirations are 18/min. Height and weight are at the 80th
percentile. The oropharynx is clear. His conjunctivae and skin are pale, and
petechiae are present on the extremities. Rubbery, nontender lymph nodes are palpable
in the cervical, axillary, and inguinal regions. Lungs are clear to
auscultation.
Hepatosplenomegaly
is present. Laboratory results are as follows:
Hemoglobin 7.8 g/dL
Hematocrit 24%
Platelets 30,000/IJL
Leukocytes 34,000/IJL
Lymphocytes 65%
Atypical lymphocytes 6%
Lymphoblasts 26%
Chest x-ray shows a
widened mediastinum. Which of the following is the best method of confirming
the diagnosis?
|
A. Bone marrow biopsy. B. Computed tomography scan of the chest . C. Lymph node biopsy . D. Magnetic resonance imaging of the
abdomen . E. Peripheral blood smear . F. Serology for Ebstein-Barr virus . G.
Serum uric acid . |
Answer : A
Explanation:
|
Acute Lymphoblastic Leukemia |
|
|
Epidemiology |
• Most common childhood cancer • Peak age: 2-5 years • Male > female |
|
Clinical features |
• Nonspecific systemic symptoms • Bone pain • Lymphadenopathy • Hepatosplenomegaly • Pallor (from anemia) •
Petechiae (from thrombocytopenia) |
|
Diagnosis |
• Bone marrow biopsy with >25%
Lymphoblasts |
|
Treatment |
•
Multi-drug chemotherapy |
Based on
clinical presentation and cancer epidemiology, this patient most likely has acute
lymphoblastic leukemia (ALL). ALL is the most common cancer in children.
The peak
incidence occurs at age 2-5 years. Boys are at increased risk of developing ALL.
Patients with Down syndrome are also at increased risk. On physical
examination, pallor and petechiae may be present due to bone marrow
infiltration resulting in anemia and thrombocytopenia, respectively. Half of
patients with ALL may have leukocytes <10,000/J.IL but >20% have
leukocytes >50,000/ J.IL. Lymphadenopathy and hepatosplenomegaly can result
from extramedullary leukemic spread. The chest x-ray finding in this patient suggests
lymphadenopathy in the mediastinum. Bone marrow biopsy is required to confirm
the type of leukemia. The presence of >25% lymphoblasts is diagnostic of
ALL.
(Choices B
and D) Imaging is performed when there is concern for metastatic
spread beyond the blood and bone marrow. However, biopsy is the only method of
determining the underlying malignancy.
(Choice
C) Because leukemia can be diagnosed by evaluation of the blood and bone marrow,
lymph node biopsy is usually unnecessary. If lymphoma is suspected or bone marrow
biopsy is equivocal for leukemia, lymph node biopsy should be performed.
(Choice E)
Peripheral blood smear is an excellent, quick, and noninvasive initial step
to assess cytopenias. Abnormal findings, such as blasts on peripheral smear,
may support the diagnosis of leukemia, but bone marrow biopsy is still required
for confirmation.
(Choice F)
Fever, hepatosplenomegaly, and atypical lymphocytosis can be seen in infectious
mononucleosis caused by Epstein-Barr virus (EBV). Hemolytic anemia and thrombocytopenia
can also be seen in EBV infection. However, the lymphadenopathy
associated
with nonmalignant illnesses is typically mobile and tender. Also, atypical lymphocytosis
is nonspecific and can be seen in many conditions. The absence of pharyngitis
and the presence of significant leukocytosis with lymphoblasts suggest leukemia
rather than EBV infection.
(Choice G) Tumor lysis syndrome is an oncologic emergency that results from tumor cell breakdown and the release of dangerous amounts of potassium, phosphate, and uric acid into the circulation. This can occur spontaneously in patients with massive lymphoma or leukemia burden or more commonly after initiation of chemotherapy. Measurement of electrolytes is extremely important but does not identify the underlying malignancy.
Educational objective:
Acute
lymphoblastic leukemia is the most common leukemia in children. The presence of
>25% lymphoblasts on bone marrow biopsy confirms the diagnosis.
|
References: 1. Acute lymphoblastic leukaemia. New
link : |
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