Hemophilia

Hemophilia – High‑Yield Study Guide for Medical Students

Definition

Hemophilia is a group of inherited bleeding disorders characterized by deficiency or dysfunction of specific coagulation factors, leading to impaired thrombin generation and defective secondary hemostasis. Classically:

• Hemophilia A: Factor VIII (FVIII) deficiency (most common).
• Hemophilia B (Christmas disease): Factor IX (FIX) deficiency.

Both are usually X-linked recessive disorders affecting males, with carrier females typically asymptomatic or mildly symptomatic depending on lyonization. Hemophilia is clinically classified by residual factor activity:

• Severe: <1% factor activity – spontaneous bleeding common.
• Moderate: 1–5% factor activity – bleeding with minor trauma.
• Mild: >5–40% factor activity – bleeding with significant trauma or surgery.

Hemophilia is a lifelong condition that requires coordinated multidisciplinary care and careful transition from pediatric to adult services to maintain optimal outcomes and continuity of prophylaxis and rehabilitation. [2]

Epidemiology

Key epidemiologic points for exam purposes:

• Hemophilia A is more common than B (roughly 4:1 to 5:1 ratio globally).
• Overall prevalence is about 1 in 5,000–10,000 live male births for hemophilia A; hemophilia B is less frequent.
• Because of the X-linked pattern, most affected individuals are males; females are typically carriers but can be symptomatic in cases of skewed X inactivation, structural X abnormalities, or compound heterozygosity. [5]
• Disease severity correlates with factor activity and is stable throughout life for a given genotype.
• Access to factor replacement and comprehensive care varies widely between high- and low-resource settings, strongly influencing morbidity and mortality.

Pathophysiology

Hemophilia results from quantitative or qualitative defects in FVIII (A) or FIX (B), which are critical components of the intrinsic pathway and tenase complex.

• Under normal conditions, FVIII/FIX complex (intrinsic tenase) activates factor X to Xa on phospholipid surfaces, amplifying thrombin generation.
• In hemophilia, deficiency of FVIII or FIX markedly reduces intrinsic tenase activity, leading to inadequate FXa and thrombin generation despite intact platelet plug formation.
• The result is defective fibrin clot stabilization and propensity to deep tissue bleeding (muscles, joints) rather than superficial mucocutaneous bleeding.

Genetics:

• X-linked recessive; mutations include large inversions (especially intron 22 inversion in F8), deletions, insertions, nonsense, or missense variants in F8 or F9.
• In female carriers, skewed X chromosome inactivation can result in lower factor levels and clinically significant bleeding, highlighting the importance of factor level testing in carriers. [5]
• In hemophilia B carriers, antenatal changes in FIX levels may differ from traditional expectations, and some data suggest that FIX can increase during pregnancy, which has implications for peripartum risk assessment and planning. [3]

Acquired complications:

• Factor inhibitors (alloantibodies) can develop after exposure to exogenous FVIII or FIX, particularly in severe hemophilia A.
• Chronic joint damage (hemophilic arthropathy) results from recurrent hemarthroses with synovial hypertrophy, cartilage destruction, and bone remodeling.

Clinical Presentation

Clinical manifestations correlate strongly with baseline factor activity.

• Severe hemophilia (<1%):
  • Spontaneous hemarthroses (knees, ankles, elbows most common).
  • Spontaneous deep muscle bleeds (iliopsoas, calf, forearm).
  • Prolonged bleeding after minor trauma, intramuscular injections, or dental work.
  • In neonates: cephalohematoma, prolonged bleeding post-circumcision, intracranial hemorrhage after relatively minor trauma.
• Moderate hemophilia (1–5%):
  • Bleeding with minor trauma and surgery.
  • Hemarthroses and muscle bleeds may occur but are less frequent and usually trauma-related.
• Mild hemophilia (>5–40%):
  • Bleeding mainly after major trauma, surgery, or invasive procedures.
  • Often diagnosed later in childhood or adulthood.

Typical features to recognize:

• Hemarthroses:
  • Joint swelling, warmth, pain, and decreased range of motion.
  • Recurrent episodes cause chronic synovitis, joint deformity, and contractures.
• Soft tissue/muscle bleeding:
  • Deep muscle hematomas can lead to compartment syndrome or nerve compression (e.g., femoral nerve with iliopsoas bleed).
• Intracranial hemorrhage:
  • Can occur spontaneously or with minor head trauma and carries high morbidity and mortality.
• Other bleeding manifestations:
  • Prolonged bleeding after dental work, tonsillectomy, or surgery.
  • Hematuria, GI bleeding, and retroperitoneal bleeding in severe cases.

Carriers and individuals with atypical X inactivation may present with menorrhagia, postpartum hemorrhage, and bleeding with procedures, emphasizing the importance of considering hemophilia carrier status in women with a suggestive family history. [5]

Diagnosis

Diagnostic evaluation integrates clinical suspicion (bleeding pattern, family history) with coagulation testing and factor assays.

• Initial screening tests:
  • Prolonged aPTT (intrinsic pathway), usually isolated.
  • Normal PT/INR, platelet count, and bleeding time/platelet function (unless another disorder coexists).
• Mixing study:
  • Patient plasma mixed 1:1 with normal plasma.
  • Correction of aPTT suggests factor deficiency (classic hemophilia).
  • Failure to correct suggests inhibitor (e.g., FVIII inhibitor) or lupus anticoagulant.
• Specific factor assays:
  • Measure FVIII and FIX activity levels to confirm hemophilia A or B and define severity.
  • Assays are also used in carriers to quantify factor levels and guide management around pregnancy or procedures. [3]
• Genetic testing:
  • Characterizes mutations in F8 or F9 (e.g., intron 22 inversion, point mutations).
  • Essential for carrier detection, prenatal diagnosis, and risk assessment for inhibitor development.
  • Also informative in families with X-linked musculoskeletal phenotypes and skewed X inactivation due to genes such as NKAP. [5]
• Inhibitor testing:
  • Bethesda assay quantifies inhibitor titer in Bethesda Units (BU).
  • High-titer inhibitors (≥5 BU) significantly impact therapeutic strategy.

In perioperative and anesthesia contexts, careful preoperative evaluation, factor assay, and plan for replacement therapy are critical, especially when other conditions (e.g., neck masses requiring surgery) co-exist. [1]

Management

Management of hemophilia centers on replacement or bypassing of the deficient factor, prevention of bleeding, treatment of acute bleeds, and management of long-term complications. Multidisciplinary comprehensive care (hematology, orthopedics, physiotherapy, dentistry, psychosocial support) is standard of care. [2]

Acute Bleeding Management

• General principles:
  • Treat suspected bleeding immediately with factor replacement before imaging or extensive work-up in high-risk areas (e.g., head, neck, iliopsoas, joints).
  • Immobilize affected joints, apply ice and analgesia (avoid NSAIDs that affect platelets).
• Factor replacement:
  • Hemophilia A: administer recombinant or plasma-derived FVIII concentrate.
  • Hemophilia B: administer recombinant or plasma-derived FIX concentrate.
  • Dosing is guided by weight, desired factor level (depending on bleed site), and pharmacokinetics; extended half-life products allow less frequent dosing.
• Adjunctive therapies:
  • Antifibrinolytics (tranexamic acid, epsilon-aminocaproic acid) for mucosal bleeding and dental procedures.
  • Desmopressin (DDAVP) for mild hemophilia A: increases endogenous FVIII and von Willebrand factor; not effective in hemophilia B.
• Management of life-threatening bleeds:
  • For intracranial hemorrhage, neck/throat bleeds, or massive GI bleeding, raise factor level rapidly to near-normal and maintain for several days.
  • Coordinate with neurosurgery, ENT, or surgery as needed.

Prophylaxis and Long-Term Management

• Primary prophylaxis:
  • Regular scheduled infusions of factor concentrate (FVIII/FIX) starting in early childhood, ideally before recurrent joint bleeding and joint damage occur.
  • Goal is to maintain trough factor levels >1% (often higher in modern regimens) to prevent spontaneous bleeds and preserve joint function.
• Secondary prophylaxis:
  • Started after onset of joint disease to reduce further bleeding and slow progression of arthropathy.
• Non-factor therapies (primarily hemophilia A):
  • Emicizumab, a bispecific monoclonal antibody that mimics FVIII cofactor function and bridges FIXa and FX, allowing for subcutaneous prophylaxis in patients with and without inhibitors.
• Inhibitor management:
  • High-titer inhibitors require bypassing agents such as activated prothrombin complex concentrate (aPCC) or recombinant activated factor VII (rFVIIa) for bleed treatment and surgery.
  • Immune tolerance induction (ITI) with frequent high-dose factor infusions aims to eradicate inhibitors over time.
• Orthopedic and rehabilitation care:
  • Physical therapy to maintain muscle strength and joint mobility.
  • Orthopedic interventions (synovectomy, joint replacement) for advanced arthropathy.
• Comprehensive care and transition:
  • Hemophilia is lifelong; structured transition from pediatric to adult care is essential to maintain adherence, address evolving comorbidities, and support independence.
  • Transition programs improve continuity of prophylaxis, adherence, and psychosocial outcomes. [2]

Perioperative and Special Situations

• Surgery and invasive procedures:
  • Require preoperative planning with hematology to define target factor levels and duration of replacement.
  • For major surgery (e.g., removal of neck masses, orthopedic procedures), FVIII or FIX levels are raised to near-normal preoperatively and maintained postoperatively with close monitoring. [1]
• Pregnancy and delivery in carriers:
  • Assess factor levels during pregnancy; FVIII usually rises, but FIX behavior in carriers of hemophilia B may differ from historical assumptions, and some carriers show increased FIX in late pregnancy. [3]
  • Delivery planning includes minimizing invasive fetal monitoring and operative vaginal delivery if the fetus is at risk.
  • Postpartum hemorrhage risk requires postpartum monitoring and sometimes prophylactic factor or antifibrinolytic therapy.
• Comorbid inherited conditions:
  • Families with X-linked musculoskeletal problems (e.g., due to NKAP mutations) may have complex phenotypes, skewed X inactivation, and overlapping skeletal and bleeding manifestations; genetic counseling is important. [5]

Key Clinical Pearls

• Isolated prolonged aPTT with normal PT and platelets in a patient with deep tissue bleeding strongly suggests hemophilia or another intrinsic pathway factor deficiency.
• Hemarthroses and deep muscle bleeds are hallmarks; mucocutaneous bleeding is less prominent than in platelet disorders or von Willebrand disease.
• Always treat suspected serious bleeds with factor replacement first; do not delay for imaging when intracranial, neck, or iliopsoas bleeding is possible.
• Inhibitors should be suspected when a previously responsive patient fails to respond to factor replacement; confirm with Bethesda assay and switch to bypassing agents.
• Carriers (especially with skewed X inactivation) can have clinically significant bleeding and require factor level assessment and tailored peripartum and perioperative management. [5]
• In hemophilia B carriers, do not assume FIX levels will remain low throughout pregnancy; recent evidence shows antenatal FIX may increase, which affects risk assessment and dosing strategies. [3]
• Early initiation of prophylaxis in children with severe hemophilia is key to preventing hemophilic arthropathy and improving long-term quality of life. [2]
• Transition from pediatric to adult care is a vulnerable period; structured programs reduce loss to follow-up and maintain adherence to prophylaxis, which is critical in a lifelong disease. [2]
• Perioperative management requires meticulous coordination between hematology, surgery, and anesthesia; challenging cases such as adult hemophilia B patients undergoing surgery for neck masses highlight the need for individualized factor replacement plans. [1]

Summary

Hemophilia is a prototypical inherited coagulation factor deficiency characterized by X-linked inheritance, defective intrinsic pathway function, and a clinical phenotype dominated by hemarthroses and deep tissue bleeding. Modern management with factor concentrates, extended half-life products, non-factor therapies, and comprehensive multidisciplinary care has dramatically improved survival and quality of life. Early diagnosis, prophylaxis, careful perioperative planning, and robust pediatric–adult transition pathways are essential to optimize outcomes in this lifelong condition. [2]