A5-year-old boy has become increasingly lethargic for past 2 months. bruising is noted on the skin of his lower legs. hb 9.2 g/dl, hct 27.8%, mcv 91 fl, platelet count 101,000/âµl, wbc count 12,128/âµl. bm biopsy shows 100% cellularity with replacement by primitive cells with large nuclei, delicate chromatin; indistinct nucleoli with scanty cytoplasm. these cells mark for cd10 (calla) antigen. which of the following is the most likely diagnosis?

Acute Lymphoblastic Leukemia (ALL)

Explanation:

The 5 year old, male patient is most likely suffering from Acute Lymphoblastic Leukemia.

INTRODUCTION:

Acute Lymphoblastic Leukemia is also known as acute lymphocytic leukemia and acute lymphoid leukemia. It is the most common cancer of children.

This disease is marked by neoplasm composed by blast cells. Blast cells are immature B or T lymphocytes.

PATHOPHYSIOLOGY:

Blast cells are marked by scant cytoplasm, larger than usual nucleus, inconspicuous (small) nucleoli and delicate chromatin. These cells stain positive for Tdt marker ( terminal deoxynucleotidyl transferase). Tdt marker is absent in mature lymphocytes but present in immature lymphocytes and acute lymphoblastic leukemic cells. Majority of ALL cells stain positive for CALLA. CALLA stands for common acute lymphoblastic leukemia antigen. CALL is also known as CD 10 (cluster of differentiation 10).

The blast cells infiltrate the bone marrow and replace it. Since RBCs are produced by the bone marrow, pathological infiltration results in the decrease in the number of RBCs produced. This may manifest as anemia with decreased Hemoglobin concentration on complete blood count/ blood complete picture test. Platelet level will also be decreased due to bone marrow infiltration. Sometimes complete blood counts may reveal increased amounts of WBCs by counting immature blast cells as WBCs.

Decreased RBCs present as symptoms of anemia with patient complaining of fatigue and lethargy. Decreased platelet counts may result in bruising on skin as the ability to heal trivial wounds is decreased.

QUESTION:

Coming back to the question, there are many cues which point towards this diagnosis.

The age of the patient i.e. 5 years old implies us to consider pediatric diseases. ALL is the most common cancer occurring in children.

Lethargy warns us to consider anemia in the patient.

Bruising points towards decreased platelets in this patient. Low blood platelet count is called thrombocytopenia.

Hb 9.2 g/dL, Hct 27.8%, MCV 91 fL confirm anemia (Normal values in children; Hgb 11-13 g/dL, Hematocrit 34%, MCV 75-90 fL) and platelet count 101,000/µL establishes thrombocytopenia (normal platelet count is 150,000-450,000 per microliter). WBC count 12,128/µL is normal ( normal values in 4-7 years children 6,000-15,000 cells per microliter) in this patient.

Replacement of bone marrow by primitive cells with large nuclei, delicate chromatin; indistinct nucleoli with scanty cytoplasm is a typical feature of Acute Lymphoblastic Leukemia.

Positive staining for CALLA establishes acute lymphoblastic leukemia in this patient as this antigen is positive in ALL cells and this disease is also implied by the symptoms, history and laboratory tests of the patient.

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