Sickle Cell Disease: Acute Complications & Chronic Management

Pathophysiology and pain crises

Mechanism. A glutamate-to-valine substitution at position 6 of β-globin produces HbS, which polymerizes when deoxygenated. Rigid, sickled cells obstruct small vessels (vaso-occlusion) and are destroyed early (chronic hemolysis). Hypoxia, dehydration, acidosis, cold, and infection promote sickling, whereas fetal hemoglobin (HbF) blocks polymerization. Symptoms therefore start after about 6 months of age as HbF falls; dactylitis—painful swelling of the hands and feet—is often the first sign.

Vaso-occlusive crisis (VOC). Treat pain as an emergency: give parenteral opioids (IV, subcutaneous, or intranasal) within 60 minutes of arrival, reassess every 15–30 minutes, and use patient-controlled analgesia when repeated doses are needed; NSAIDs can be added if kidney function allows, while oral acetaminophen alone is inadequate and meperidine is avoided. Hydrate carefully—at no more than maintenance rates once euvolemic—because overhydration can precipitate acute chest syndrome. Give oxygen only for hypoxemia, prescribe incentive spirometry, and do not transfuse for an uncomplicated crisis.

Acute chest syndrome and stroke

Acute chest syndrome (ACS). A new segmental infiltrate plus fever, chest pain, tachypnea, cough, or hypoxemia, often developing 1–3 days into a pain crisis. Causes include infection (atypical organisms such as Chlamydophila and Mycoplasma, and viruses), fat embolism from infarcted marrow, and hypoventilation from rib infarcts or opioid sedation. A vicious cycle follows: lung injury causes hypoxemia, which deoxygenates more HbS and worsens pulmonary vaso-occlusion. ACS is a leading cause of death in sickle cell disease.

Treating ACS. Give a third-generation cephalosporin plus a macrolide (ceftriaxone + azithromycin), adding vancomycin for severe illness; oxygen for hypoxemia; incentive spirometry; and analgesia. Simple transfusion is used for moderate disease or a falling hemoglobin; exchange transfusion for severe or rapidly worsening hypoxemia or progressive infiltrates. Do not overhydrate, and do not transfuse above 10 g/dL.

Stroke. Ischemic stroke risk peaks in childhood, while hemorrhagic stroke is more common in young adults. Acute ischemic stroke calls for urgent exchange transfusion to lower HbS below 30% while keeping hemoglobin near 10 g/dL, followed by chronic transfusion to prevent recurrence; thrombolysis is not the standard in children with sickle cell stroke.

Primary prevention. Screen children with HbSS or HbSβ0-thalassemia by transcranial Doppler (TCD) every year from age 2 to 16. A time-averaged mean velocity ≥200 cm/s in the internal carotid or middle cerebral artery warrants chronic transfusion to keep HbS below 30%, which reduced first strokes by about 90% in the STOP trial. After at least 1 year of transfusions without severe vasculopathy, hydroxyurea can replace transfusion (TWiTCH trial).

Other acute emergencies

Aplastic crisis. Parvovirus B19 enters erythroid precursors through the P antigen and halts red cell production; because sickle cells survive only days to weeks, hemoglobin plunges and reticulocytes almost disappear.

Splenic sequestration. Red cells pool in the spleen before it autoinfarcts, so the classic patient is a young child with HbSS (older children and adults with HbSC keep their spleens longer). As the episode resolves, the spleen releases trapped cells, so transfuse small aliquots to avoid overshooting the hemoglobin. Teach parents to palpate the spleen.

Priapism. Sickled cells trapped in the corpora cause ischemic priapism. Hydration and analgesia are started but must not delay urologic aspiration beyond 4 hours, because prolonged ischemia causes fibrosis and impotence. Exchange transfusion alone is not recommended as primary therapy.

Infection. Repeated splenic infarction produces functional asplenia by about age 5 (Howell-Jolly bodies on smear), leaving patients vulnerable to encapsulated organisms—S. pneumoniae, H. influenzae, N. meningitidis—and to Salmonella.

Osteomyelitis vs bone infarction. Infarction is far more common, but osteomyelitis—classically Salmonella (seeded from bowel microinfarcts and poorly filtered by the damaged spleen), also S. aureus—must be excluded when fever persists. MRI cannot reliably separate the two, so obtain blood cultures and bone aspirate or biopsy cultures.

Chronic complications

• Bone. Avascular necrosis of the femoral (and humeral) head causes groin pain with weight bearing; MRI detects early disease. Treat with analgesia and core decompression, then arthroplasty.
• Skin. Chronic leg ulcers near the malleoli heal slowly.
• Kidney. Medullary sickling causes isosthenuria—a fixed urine specific gravity near 1.010—with nocturia, enuresis, and rapid dehydration, plus papillary necrosis with painless hematuria. Hyperfiltration leads to albuminuria, FSGS, and CKD; treat albuminuria with an ACE inhibitor or ARB.
• Eye. Proliferative retinopathy, most common in HbSC disease despite its milder anemia; dilated eye exams every 1–2 years from age 10.
• Lung and heart. Pulmonary hypertension; a tricuspid regurgitant jet ≥2.5 m/s on echocardiography predicts higher mortality.
• Gallbladder. Pigment gallstones from chronic hemolysis; cholecystectomy for symptomatic disease.
• Iron overload. From chronic transfusion; follow ferritin and liver MRI, and chelate with deferasirox or deferoxamine.

Sickle cell trait

People with HbAS have no anemia or pain crises but can develop isosthenuria and painless hematuria from papillary necrosis, exertional rhabdomyolysis and heat illness with extreme exertion (prevented by hydration and acclimatization), and renal medullary carcinoma—an aggressive tumor of young adults seen almost exclusively with sickle hemoglobinopathies.

Disease-modifying therapy and prevention

Hydroxyurea. This ribonucleotide reductase inhibitor raises HbF and reduces pain crises, ACS, transfusion needs, and mortality. Offer it to all children with HbSS from 9 months of age and to adults with ≥3 painful crises a year, prior ACS, or severe symptomatic anemia. Myelosuppression is dose-limiting, so the dose is titrated to the maximum tolerated level with CBC, differential, and reticulocyte monitoring for neutropenia and thrombocytopenia. It is teratogenic, so contraception is required. A rising MCV and HbF are expected and serve as a check on adherence.

Other agents and cures. L-glutamine (which reduces red cell oxidative stress) and crizanlizumab (an anti-P-selectin antibody; its confirmatory trial did not show fewer crises) are add-on options. Voxelotor, an HbS polymerization inhibitor, was withdrawn from the market in 2024 over safety concerns. Matched-sibling allogeneic HSCT is curative and works best in children. Gene therapy is available for patients ≥12 years with recurrent crises: exa-cel uses CRISPR editing to raise HbF, and lovo-cel adds an anti-sickling β-globin gene.

Transfusion principles

Alloimmunization. Repeated exposure to donor antigens makes patients with sickle cell disease prone to alloantibodies, so give leukoreduced units matched for an extended phenotype (at least Rh C and E and Kell).

A delayed hemolytic transfusion reaction 5–14 days after transfusion mimics a pain crisis—pain, dark urine, jaundice, a new alloantibody (e.g., anti-E), and hemoglobin falling below the pretransfusion level (hyperhemolysis). Avoid further transfusion if possible, because it can worsen hemolysis.