Neurological & Cardiopulmonary Complications

Pathophysiology & Features	Management
- Silent cerebral infarction: MRI T2-weighted hyperintensities lacking focal deficit.- Prevalence 39% in HbSS children.- Causes neuropsychological deficits, impaired school performance.- Progresses to overt stroke.	- Neuropsychological testing, academic performance monitoring.- Chronic red cell transfusion therapy.- Target hemoglobin > 9 g/dL, HbS < 30%.

Pathophysiology & Features	Management
- Chronic anemia induces compensatory increased cardiac output.- Cardiomegaly, left ventricular hypertrophy (50% prevalence).- Prolonged QTc, systolic flow murmur.- Pulmonary hypertension: Elevated tricuspid regurgitant velocity (TRV $\ge$ 2.5 cm/s).	- Echocardiogram, right-heart catheterization.- Hydroxyurea, red cell transfusions.- Avoid Sildenafil (increases vaso-occlusive pain risk).

Pathophysiology & Features	Management
- Reduced PaO2, decreased oxygen saturation.- Chronic lung disease/pulmonary fibrosis: Major mortality cause in young adults.- Asthma: Higher prevalence, linked to acute chest syndrome/stroke.	- Pulmonary function testing.- Prophylactic transfusions to prevent end-stage fibrosis.- Aggressive asthma management (avoid systemic steroids to prevent rebound vaso-occlusion).

Renal & Hepatobiliary Complications

Pathophysiology & Features	Management
- Increased renal flow/GFR, kidney enlargement.- Hyposthenuria (concentration defect via vasa recta obliteration), causing nocturia/enuresis.- Renal tubular acidification defect, hyponatremia.- Proteinuria, nephrotic syndrome, chronic renal failure.	- Enuresis: Behavioral modifications, bedtime 1-deamino-8-D-arginine vasopressin (DDAVP).- Proteinuria (>4-8 weeks): Angiotensin-converting enzyme (ACE) inhibitors.- Diuretics for nephrotic edema.

Pathophysiology & Features	Management
- Chronic hepatomegaly, elevated AST/ALT.- Cholelithiasis: Pigmented stones from chronic hemolysis (30% prevalence by age 18).- Intrahepatic sickling crisis, hepatic necrosis, portal fibrosis, cirrhosis.- Transfusion-related hepatitis C, iron overload fibrosis.	- Sonographic screening.- Laparoscopic cholecystectomy for symptomatic gallstones.- Exchange transfusion for intrahepatic crisis.- Chelation therapy for transfusional iron overload.

Pathophysiology & Features	Management
- Marrow expansion: Cortical thinning, "hair-on-end" skull, "fish-mouth" vertebrae.- Avascular Necrosis (AVN): Femoral/humeral head destruction via ischemia-reperfusion injury.- Cumulative incidence 22%.- Chronic pain, limited joint mobility.	- Annual musculoskeletal physical exams, MRI screening.- Early stage AVN: Core decompression.- Late stage AVN: Total hip replacement utilizing cementless grafts.

Pathophysiology & Features	Management
- Cutaneous leg ulcers located over internal/external malleoli.- Result of increased venous pressure from expanded marrow blood volume.	- Rest, elevation, soft sponge-rubber doughnut.- Debridement, elastic stockings, oral zinc sulfate.- Refractory cases: Transfusion therapy (3-6 months), split-thickness skin grafts.

Pathophysiology & Features	Management
- Eyes: Nonproliferative retinopathy (small vessel occlusion).- Proliferative retinopathy: Neovascularization ("sea fans"), vitreous hemorrhage, retinal detachment.- Angioid streaks, hyphema.- ENT: High-frequency sensorineural hearing loss.- Adenotonsillar hypertrophy (compensation for splenic lymphoid loss), causing obstructive sleep apnea/hypoxemia.	- Eyes: Annual ophthalmologic exams (starting age 8 for HbSS, age 5 for HbSC).- Laser photocoagulation.- Anterior chamber paracentesis for hyphema.- ENT: Sleep study.- Early tonsillectomy and adenoidectomy.

Pathophysiology & Features	Management
- Growth: Delayed height/weight, delayed puberty. Catch-up growth by late adolescence.- Hyposplenism: Autosplenectomy via progressive fibrosis by early childhood. High risk of fatal sepsis (S. pneumoniae, H. influenzae b).- Iron Overload: Secondary to repeated transfusions.	- Infection: Oral penicillin prophylaxis, immunizations (PCV-13, PPV-23, Meningococcal).- Overload: Iron chelation (Deferoxamine, Deferasirox, Deferiprone).

Hydroxyurea: Increases Fetal Hemoglobin (HbF), decreases red cell adhesion, lowers neutrophils/reticulocytes. Reduces vaso-occlusive episodes, acute chest syndrome, and mortality. Monitor complete blood counts monthly.
L-Glutamine: Alters RBC redox state, decreases adhesion. Reduces pain episodes and hospitalizations.
Voxelotor: HbS polymerization inhibitor, reduces hemolysis.
Crizanlizumab: Anti-P-selectin antibody, prevents vaso-occlusive pain episodes.
Chronic Transfusion Therapy: Target HbS < 30%. Requires extended phenotyping (C, E, K matching) to prevent alloimmunization.

Hematopoietic Stem Cell Transplant (HSCT): Only curative therapy currently established. Indicated for stroke, recurrent acute chest syndrome, debilitating pain, severe nephropathy. Best outcomes with HLA-matched sibling donors.
Gene Therapy: Ex-vivo CD34+ modification. Uses lentiviral vectors (Lentiglobin BB305) or CRISPR/Cas9 editing (BCL11A repressor) to induce HbF or add functional $\beta$-globin variants.