Hyposplenism refers to reduced or absent splenic function, which leads to impaired immune response and increased susceptibility to infections. Understanding its causes, consequences, and management is essential for UKMLA.

Aetiology:

1. Congenital:
   • Asplenia or polysplenia syndromes.
2. Acquired:
   • Splenectomy: Surgical removal of the spleen (e.g., trauma, malignancy).
   • Sickle Cell Disease: Autosplenectomy due to repeated infarctions.
   • Coeliac Disease: Associated with functional hyposplenism.
   • Inflammatory Bowel Disease: Especially Crohn’s disease.
   • Systemic Lupus Erythematosus.
   • HIV/AIDS: Secondary to immune dysfunction.
   • Alcoholic Liver Disease.

Pathophysiology:

• The spleen plays a crucial role in filtering abnormal red cells and opsonising encapsulated bacteria.
• Loss of splenic function leads to reduced phagocytosis, complement activation, and antibody production.

Clinical Features:

1. Asymptomatic:
   • Many patients are asymptomatic and diagnosed during investigations.
2. Recurrent or Severe Infections:
   • Particularly with encapsulated organisms (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis).
3. Thrombocytosis:
   • High platelet count due to loss of splenic sequestration.
4. Howell-Jolly Bodies:
   • Presence of nuclear remnants in red blood cells on peripheral blood film (indicative of hyposplenism).

Investigations:

1. Peripheral Blood Film:
   • Howell-Jolly bodies, target cells, acanthocytes.
2. Full Blood Count (FBC):
   • Thrombocytosis, mild leukocytosis.
3. Imaging:
   • Ultrasound or CT to assess spleen size and structure.
4. Functional Tests:
   • Pitted red cell count or scintigraphy for functional assessment (rarely performed in routine practice).

Management:

1. Prophylactic Vaccination:
   • Vaccines against encapsulated bacteria:
     • Pneumococcal (e.g., PCV13 and PPV23).
     • Meningococcal (e.g., MenACWY, MenB).
     • Haemophilus influenzae type b (Hib).
     • Influenza vaccine annually.
2. Antibiotic Prophylaxis:
   • Lifelong low-dose penicillin V (especially for splenectomy patients and children).
3. Patient Education:
   • Awareness of infection risks and seeking prompt medical attention for febrile illness.
4. Infection Management:
   • Empirical antibiotics for febrile illnesses (e.g., amoxicillin or levofloxacin if penicillin-allergic).
5. Other Measures:
   • Malaria prophylaxis for travel to endemic areas.
   • Avoidance of animal bites (e.g., risk of Capnocytophaga canimorsus infection).

Complications:

1. Severe Infections:
   • Overwhelming post-splenectomy infection (OPSI): High mortality, rapid onset sepsis.
2. Thrombosis:
   • Increased risk of thrombotic events (e.g., deep vein thrombosis, pulmonary embolism).
3. Haematological:
   • Persistent thrombocytosis, leading to hypercoagulability.

Prognosis:

• Good with appropriate vaccination and prophylaxis.
• High risk of life-threatening infections without preventive measures.

Key Exam Points for UKMLA:

1. Diagnosis:
   • Howell-Jolly bodies on blood film and history of splenectomy or splenic dysfunction.
2. Infections:
   • High-risk pathogens are encapsulated organisms (Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae).
3. Prophylaxis:
   • Ensure vaccination and antibiotic prophylaxis in all patients with hyposplenism.
4. Complications:
   • Focus on OPSI as a medical emergency.
5. Differentials:
   • Consider other causes of recurrent infections (e.g., primary immunodeficiencies).