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Updated: Jan 6 2018

Hyper IgM Syndrome

Images
https://upload.medbullets.com/topic/105012/images/hyperigm syndrome.jpg
https://upload.medbullets.com/topic/105012/images/bcellclassswitching.jpg
  • Snapshot
    • A 6-month-old boy presents with a past medical history of skin infections presents with difficulty breathing, high fever, and nonproductive cough. He is immediately started on broad-spectrum antibiotics. On further questioning, his family history includes a maternal uncle dying at age 20 from overwhelming pneumonia. Sputum is induced with hypertonic saline inhalation, and eventual staining shows Pneumocystis. He is immediately started on IVIG.
  • Introduction
    • Inherited primary combined B- and T-cell immunodeficiency characterized by increased levels of IgM
    • Genetics
      • X-linked recessive
      • mutation in gene that codes for CD40 ligand (CD40L)
    • Pathogenesis
      • CD40L is expressed on activated T-helper cells
      • defect in humoral immunity
        • CD40L is necessary to induce B-cells to undergo Ig class-switching
          • from IgM to IgG, IgA, and IgE
          • see illustration above
      • defect cell-mediated immunity
        • CD40L also required for maturation of T-cells, dendritic cells, and macrophages
    • Symptoms onset by 1 year, often with Pneumocystis infections
      • most diagnosed before 4 years
  • Presentation
    • Symptoms
      • severe pyogenic infections early in life
      • chronic diarrhea
      • opportunistic infections
        • pneumonia
        • Pneumocystis
        • Cryptosporidium
        • CMV
        • echovirus encephalitis
      • pancytopenia common
        • fatigue
        • infection
        • pallor
        • bleeding
  • Evaluation
    • Ig levels
      • ↑ IgM
      • ↓ IgA, IgG, and IgE
      • due to defect in class-switching
    • Diagnosis confirmed with flow cytometry
      • deficient expression of CD40L on activated T-helper cells
      • normal T- and B-cells
    • CBC
      • neutropenia
      • thrombocytopenia possible
  • Differential Diagnosis
    • Bruton agammaglobulinemia
    • CVID
    • SCID
  • Treatment
    • Prophylaxis of Pneumocystis
    • Regular IVIG replacement
  • Prognosis, Prevention, and Complications
    • Prognosis
      • 20% survival rate past young adulthood
      • leading cause of death
        • pneumonia
        • encephalitis
        • malignancy
    • Complications
      • increased risk of autoimmunity
      • increased risk of malignancies
        • HCC
        • carcinoid tumor
      • infection
      • bronchiectasis
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