Clinical scenario: Sickle cell disease | pallor | rash
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.
