Sickle Cell Disease, SAM, and Thalassemia

1. SICKLE CELL DISEASE (SCD)

Definition & Epidemiology

Pathogenesis

• Normal adult RBC: 96% HbA (α₂β₂), 3% HbA₂, 1% HbF
• In SCD: HbA is completely replaced by HbS; in carriers (sickle trait), ~40-50% is HbS
• On deoxygenation, HbS undergoes conformational change → molecules polymerize via the abnormal valine residue → distort RBC into elongated, crescentic (sickle) shape
• Initial sickling is reversible on reoxygenation, but repeated episodes cause cumulative membrane damage (Ca²⁺ influx, K⁺ and water loss), creating irreversibly sickled cells

Three Key Factors Determining Clinical Severity

1. Intracellular levels of non-HbS hemoglobins - HbA and HbF inhibit HbS polymerization. Newborns are protected until HbF falls (~5-6 months). Carriers have HbA that greatly retards sickling.
2. MCHC (Mean Corpuscular Hemoglobin Concentration) - higher MCHC = denser cells = more polymerization. Loss of water from RBCs raises MCHC and accelerates sickling.
3. Transit time through microcirculation - slower blood flow (e.g., in hypoxic/acidotic states) gives HbS longer to polymerize.

Consequences of Sickling

Sickle Cell Trait vs. Disease

• Trait (HbAS): ~40% HbS + ~60% HbA → generally asymptomatic, minimal sickling in vivo; rare complications under severe hypoxia
• Disease (HbSS): 100% HbS → full clinical picture

Blood Smear

Management Principles

• HbF induction: Hydroxyurea (↑ HbF, reduces sickling)
• Analgesics for pain crises
• Penicillin prophylaxis + vaccinations (asplenic state)
• Blood transfusions for severe anemia/stroke
• Bone marrow transplant (curative)
• Gene therapy (emerging)

2. SEVERE ACUTE MALNUTRITION (SAM)

Definition (WHO)

SAM Spectrum: Two Ends

Additional SAM Features (Both Forms)

• Immune deficiency (especially T-cell mediated) → concurrent infections common
• Anemia and multivitamin deficiencies
• Gut microbiome alterations (play a causative role, not just consequence)
• Infections impose additional catabolic stress, worsening malnutrition

Diagnosis

• Weight-for-height Z-score (primary)
• Skinfold thickness (fat stores)
• Midarm circumference (muscle mass): <12.5 cm = severe; 12.5-13.5 cm = mild-moderate; >13.5 cm = normal
• Serum albumin/transferrin (visceral protein compartment)

Prevention (FAO/WHO Framework)

• Breastfeeding promotion
• Supplementary feeding for pregnant/lactating women
• Low-cost weaning foods
• Nutrition education
• Family planning and birth spacing

3. THALASSEMIA

Definition

Pathogenesis (Two Mechanisms of Anemia)

1. Inadequate HbA formation → small (microcytic), poorly hemoglobinized (hypochromic) RBCs
2. Accumulation of unpaired globin chains → toxic precipitates → membrane damage → apoptosis of erythroid precursors in bone marrow = ineffective erythropoiesis

• Low hepcidin → ↑ iron absorption → iron overload (even without transfusions)
• Massive extramedullary hematopoiesis → hepatosplenomegaly, skeletal deformities ("chipmunk facies" from frontal bossing in β-thalassemia major)

Classification

β-Thalassemia (mainly point mutations)

α-Thalassemia (mainly gene deletions - 2 genes per chromosome 16)

Key Lab Findings

• Microcytic hypochromic anemia (low MCV, MCH)
• Target cells on peripheral smear
• Elevated HbA₂ (>3.5%) and/or HbF on Hb electrophoresis → diagnostic for β-thal minor
• HbH inclusions (Heinz body-like, with BCB stain) in HbH disease
• No HbA₂ elevation in α-thalassemia

Management

• β-Thal major: Regular blood transfusions (every 3-4 weeks) + iron chelation (deferoxamine, deferasirox, deferiprone) + splenectomy (if hypersplenism), bone marrow transplant (curative), luspatercept (activin receptor ligand trap, reduces ineffective erythropoiesis)
• β-Thal minor: No treatment; genetic counseling
• HbH: Folic acid; transfuse during hemolytic crises; avoid oxidant drugs
• Hydrops fetalis: Intrauterine transfusion (to allow delivery); otherwise fatal

Comparison at a Glance

Diagnosis and Management of Sickle Cell Pain Crisis (Vaso-Occlusive Crisis)

What Is a Pain Crisis?

DIAGNOSIS

Clinical Diagnosis - There Is No Lab Test for Crisis

"No test is available that detects whether a patient is in a crisis - the diagnosis is based largely on clinical presentation." - Rosen's Emergency Medicine

History

• Duration and location of pain
• Fever (low-grade fever can occur in VOC itself; high fever suggests infection)
• Focal swelling or redness
• Precipitating factors: cold exposure, dehydration, infection, exertion, hypoxia, alcohol, high altitude/pressurized aircraft
• Medications already taken
• Prior episodes - is this similar to previous crises? (atypical pain = red flag)

Physical Examination

WBC >20,000/mm³ with increased bands is NOT typical for simple VOC - suggests infection.

Investigations

• Retic <3% (or below patient's usual): suggests aplastic crisis (parvovirus B19)
• Retic >12% with nucleated RBCs: suggests rapid hemolysis

Peripheral Blood Smear in SCD

MANAGEMENT

General Goals

"Rest, adequate nutrition, hydration, oxygenation, analgesia, transfusion, and therapy for infection - directed toward symptomatic relief and interrupting the cycle of deoxygenated sickling and intravascular sludging." - Rosen's Emergency Medicine

Step 1: Immediate Supportive Measures

Step 2: Analgesia (Core of Management)

"Analgesia is a major benefit and essential early therapy for acute sickle cell vaso-occlusive crises." - Rosen's Emergency Medicine

Opioid Protocol (Adults and Children >50 kg):

• IV Morphine sulfate: 5-10 mg every 2-4 hours, OR
• IV Hydromorphone: 1.5 mg every 3-4 hours

Opioid Protocol (Children <50 kg):

• IV Morphine: 0.1-0.15 mg/kg every 2-4 hours, OR
• IV Hydromorphone: 0.015-0.020 mg/kg every 3-4 hours
• Intranasal fentanyl (INF): Useful in pediatric patients - individual studies show potential benefit for timely repeat dosing and IV-sparing

Adjuncts:

• NSAIDs (ketorolac, ibuprofen): Opioid-sparing effect; reduce opioid-related adverse events; generally well accepted. Use with caution in renal impairment.
• Acetaminophen/paracetamol: Safe adjunct
• Patient-controlled analgesia (PCA): Preferred for admitted patients with severe or recurrent crises

Note: A 2026 meta-analysis (PMID: 42190636) found no significant difference between early vs delayed opioid administration in pediatric VOC for hospital admission, ED discharge, or ED length of stay - though individual studies support timely repeat dosing and use of intranasal fentanyl.

Step 3: Reassessment at 4-6 hours

• Pain controlled, tolerating oral intake → discharge with oral analgesics + close follow-up
• Pain not controlled, requiring IV opioids → admit

Indications for Admission

• Pain not controlled with IV opioids at 4-6 hours
• Acute Chest Syndrome (ACS) (new pulmonary infiltrate + fever/respiratory symptoms)
• Stroke (focal neurologic signs)
• Aplastic crisis (Hb drop >2 g/dL, reticulocyte count <3%)
• Splenic or hepatic sequestration
• Fever with suspected sepsis
• Priapism >4 hours
• Severe vomiting/dehydration, inability to tolerate oral intake

SPECIAL ACUTE PRESENTATIONS TO RECOGNIZE

Acute Chest Syndrome (ACS)

• New pulmonary infiltrate on CXR + ≥1 of: fever, cough, tachypnea, chest pain, hypoxia
• Management: O₂, hydration, antibiotics (atypical coverage: macrolide + cephalosporin), bronchodilators, simple or exchange transfusion, possible corticosteroids (controversial - ↑ readmission risk)
• Exchange transfusion if PaO₂ <60 mmHg (target HbS <30%)

Abdominal Crisis

• Generalized constant abdominal pain - can mimic cholecystitis/appendicitis
• VOC should be accompanied by MSK pain; patient often recognizes it as similar to prior episodes; no peritoneal signs
• Repeated exams are mandatory to detect developing peritonitis

Splenic/Hepatic Sequestration

• Sudden massive pooling of blood in spleen (children) or liver
• Features: acute severe anemia + organomegaly + reticulocytosis
• Tx: IV fluids + blood transfusion (exchange if hepatic)

LONG-TERM / DISEASE-MODIFYING THERAPY (Prevent Future Crises)

Summary Flow

Acute pain in known SCD patient
        ↓
Assess: vitals, SpO₂, fever, CBC, retic, CXR if respiratory symptoms
        ↓
Rule out: ACS, stroke, infection, sequestration, aplastic crisis
        ↓
Start: IV fluids + analgesia (opioid ± NSAID) + O₂ only if SpO₂ <95%
        ↓
Reassess at 4-6 hrs
        ↓
Pain controlled → Discharge with oral analgesics + follow-up
Pain uncontrolled / complications → Admit