Clinical Scenario:
n 8-year-old boy with homozygous sickle cell disease (HbSS) presents with increasing lethargy and pallor for 2 days. One week earlier, he had a low-grade fever and a mild erythematous rash that resolved spontaneously. There is no history of bone pain or respiratory symptoms.
On examination:
- Temperature: 37.2°C
- Heart rate: 138/min
- Blood pressure: 100/60 mmHg
- Marked pallor
- Mild scleral icterus
- Spleen is not enlarged compared with previous examinations.
Investigations:
- Hemoglobin: 3.9 g/dL (baseline 8.2 g/dL)
- Reticulocyte count: 0.2%
- WBC count: 6.8 × 10⁹/L
- Platelets: 290 × 10⁹/L
- Bilirubin: 1.8 mg/dL
What is the most likely diagnosis?
A. Acute splenic sequestration crisis
B. Aplastic crisis due to parvovirus B19
C. Hyperhemolytic crisis
D. Vaso-occlusive crisis
E. Acute chest syndrome
Correct answer & Explanation:
Correct Answer: B. Aplastic crisis due to parvovirus B19
Explanation:
This child has an aplastic crisis, classically caused by parvovirus B19, which infects erythroid precursor cells and temporarily suppresses erythropoiesis.
The key diagnostic clue is:
- Profound anemia with a markedly low reticulocyte count
Patients with sickle cell disease rely on continuous reticulocytosis because of chronic hemolysis. Temporary cessation of red cell production can therefore cause a dramatic fall in hemoglobin.
The preceding viral illness with a rash further supports parvovirus B19 infection.
Management includes:
- Packed red blood cell transfusion if symptomatic or severely anemic
- Supportive care
- Recovery of erythropoiesis usually occurs within 7–10 days.
Why the other options are incorrect
A. Acute splenic sequestration crisis
- Causes sudden splenic enlargement, hypovolemia, and high reticulocyte count due to ongoing marrow compensation.
C. Hyperhemolytic crisis
- Characterized by increased hemolysis with reticulocytosis, rising bilirubin, and worsening jaundice.
D. Vaso-occlusive crisis
- Presents with severe pain and does not typically cause profound reticulocytopenia.
E. Acute chest syndrome
- Requires a new pulmonary infiltrate with respiratory symptoms, which are absent here.
High-yield pearl (MRCPCH/FCPS/MD)
| Complication | Reticulocyte Count | Spleen | Key Feature |
|---|---|---|---|
| Aplastic crisis | Low | Normal | Parvovirus B19 suppresses erythropoiesis |
| Splenic sequestration | High | Enlarged | Acute splenic pooling with hypovolemia |
| Hyperhemolytic crisis | High | Usually unchanged | Accelerated hemolysis with jaundice |
Exam tip: In a child with sickle cell disease, a sudden drop in hemoglobin with reticulocytopenia is aplastic crisis until proven otherwise.
Reference:
Yee MEM, Kalmus GG, Patel AP, et al. Increase in Diagnoses of Human Parvovirus B19–Associated Aplastic Crises in Children and Adolescents with Sickle Cell Disease. MMWR Morb Mortal Wkly Rep. 2024;73:1090–1091.
You can also solve another MCQ on Sickle Cell Anemia.
