Most Likely Diagnosis: Aplastic Anemia
The most likely diagnosis is aplastic anemia (option c), given the presentation of pancytopenia (fatigue, pallor, sore throat, petechiae) with severe thrombocytopenia and leukopenia in the absence of features suggesting acute leukemia or isolated ITP. 1, 2
Clinical Reasoning
Why Aplastic Anemia is Most Likely
Pancytopenia with characteristic symptoms: The patient presents with the classic triad of anemia (fatigue, pallor), neutropenia (sore throat suggesting infection risk), and thrombocytopenia (petechiae) 2, 3
Laboratory pattern: Platelets of 15,000/μL combined with WBC of 3,800/μL represents involvement of multiple cell lines, which is the hallmark of bone marrow failure syndromes 1, 3
Absence of splenomegaly: The lack of splenomegaly strongly suggests primary bone marrow pathology rather than peripheral sequestration or hypersplenism 1
Why Other Options Are Less Likely
ITP (option a) is excluded because:
- ITP presents with isolated thrombocytopenia, not pancytopenia 4
- The WBC count would be normal or elevated in ITP, not decreased at 3,800/μL 4
- Physical examination in ITP shows no other abnormalities beyond bleeding manifestations 4
Leukemia (option b) is less likely because:
- Acute leukemia typically presents with elevated WBC counts (often >20,000/μL), not leukopenia 4
- Leukemia would show abnormal cells (blasts) on peripheral smear 4
- Patients with leukemia often have hepatosplenomegaly and lymphadenopathy, which are not mentioned here 4
"Bone marrow failure" (option d) is essentially synonymous with aplastic anemia, making option c the more specific and correct answer 2, 3
Immediate Diagnostic Approach
Bone marrow aspiration and biopsy with cytogenetic analysis must be performed immediately to confirm the diagnosis and exclude other causes of pancytopenia 1, 5
Key diagnostic studies required:
Peripheral blood smear: To assess for dysplastic features, abnormal cells, or morphologic abnormalities that would suggest MDS or leukemia 1, 5
Reticulocyte count: Expected to be low (<1%) in aplastic anemia, indicating decreased bone marrow production 1, 3
Vitamin B12 and folate levels: To exclude megaloblastic anemia, a reversible cause of pancytopenia 6, 5
Viral serologies: HIV, hepatitis B and C, as viral infections can cause secondary aplastic anemia 5, 3
Critical Management Priorities
Immediate Risk Stratification
This patient requires urgent hospitalization given:
- Platelets <20,000/μL with bleeding manifestations (petechiae) 5
- WBC 3,800/μL suggesting neutropenia (absolute neutrophil count likely <1,500/μL) 1, 6
- Signs of infection risk (sore throat) 1, 6
Supportive Care Measures
Infection control for neutropenia (if ANC <500/μL):
- Implement strict infection control measures 1, 6
- Monitor temperature every 4 hours 6, 5
- Consider prophylactic antibiotics if neutropenia persists 6, 5
- Initiate Filgrastim (G-CSF) 5 μg/kg/day subcutaneously until ANC >1,000/μL 1, 6
Bleeding precautions for severe thrombocytopenia:
- Consider platelet transfusion for platelets <10,000/μL or active bleeding 1, 6
- Avoid antiplatelet agents and NSAIDs 1
Anemia management:
- Transfuse packed red blood cells if hemoglobin <7 g/dL 6
Common Pitfalls to Avoid
Do not assume ITP based solely on low platelets and petechiae: Always check the complete blood count for involvement of other cell lines 4, 1
Do not delay bone marrow examination: This is mandatory for definitive diagnosis and cannot be replaced by peripheral blood studies alone 1, 5
Do not overlook reversible causes: Megaloblastic anemia and drug-induced pancytopenia can mimic aplastic anemia but are treatable with specific interventions 6, 7
Pancytopenia with hypoplastic bone marrow requires differentiation from hypoplastic MDS: Look for dysplastic features, increased blasts (>5%), and cytogenetic abnormalities that favor MDS over aplastic anemia 4, 8
Prognostic Factors
Negative prognostic indicators in aplastic anemia include: