Sickle Cell Vaso-Occlusive Crisis
Hematology
Illness script · Hematology
Sickle Cell Vaso-Occlusive Crisis
Acute pain crisis in sickle cell disease caused by sickling of RBCs occluding microvasculature, causing ischemia and infarction.
This illness script for Sickle Cell Vaso-Occlusive Crisis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Homozygous HbSS (most severe) > HbSC, HbS-β-thalassemia
- Triggers: infection (esp. parvovirus B19), cold exposure, dehydration, hypoxia, stress
- More frequent crises in patients with higher baseline WBC or lower HbF
- African descent predominantly; ~1/365 Black Americans born with SCD
- Prior crisis frequency predicts future crisis risk
02
Presentation
- Severe, acute bone pain (back, chest, extremities, abdomen) — most common complaint
- Dactylitis (hand-foot syndrome): earliest manifestation in infants <2 years
- Fever may accompany crisis (but always rule out infection)
- Acute chest syndrome: fever + chest pain + new pulmonary infiltrate — life-threatening
- Splenic sequestration: acute left upper quadrant pain + splenomegaly + rapid anemia in young children
- Avascular necrosis of femoral/humeral head with recurrent crises
03
Pathophysiology
- HbS polymerizes under low O₂ tension → RBCs deform into sickle shape
- Sickled cells are rigid, adhesive → occlude small vessels → ischemia/infarction
- Hemolysis → anemia + endothelial dysfunction → NO depletion → vasoconstriction
- Reperfusion injury and inflammation amplify pain and organ damage
04
Diagnostics
- Diagnosis is clinical in known SCD patient with typical pain pattern
- CBC: normocytic anemia (baseline Hgb ~7-8), elevated reticulocyte count
- Peripheral smear: sickle cells, target cells, Howell-Jolly bodies (functional asplenia)
- Chest X-ray + SpO₂ essential to exclude acute chest syndrome
- Newborn screen (Hgb electrophoresis/HPLC) is gold standard for SCD diagnosis
- Parvovirus B19 infection causes aplastic crisis: reticulocyte count drops to near zero
05
Management
- IV hydration (correct dehydration, avoid overload — risk of acute chest syndrome)
- Aggressive multimodal analgesia: IV opioids (morphine/hydromorphone) + NSAIDs + acetaminophen; avoid meperidine
- Incentive spirometry to prevent splenic sequestration and acute chest syndrome
- Acute chest syndrome: O₂, antibiotics (covers atypicals), exchange transfusion if severe
- Hydroxyurea (increases HbF): long-term disease-modifying therapy, reduces crisis frequency
- Hematopoietic stem cell transplant: only curative option; gene therapy emerging
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Acute Chest Syndrome
New pulmonary infiltrate on CXR + hypoxia distinguishes ACS from uncomplicated VOC
Aplastic Crisis (Parvovirus B19)
Reticulocyte count near zero (not elevated) despite worsening anemia — bone marrow suppression
Osteomyelitis
Dactylitis or bone pain in SCD mimics OM; MRI + bone culture distinguish; Salmonella is classic SCD pathogen
Acute Abdomen / Mesenteric Ischemia
Abdominal VOC has normal bowel sounds and no peritoneal signs; surgical abdomen has guarding/rigidity
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.