Differential Diagnosis

The patient presents with a normal T cell count, low CD19+ (indicating low B cell count), and low IgG levels, along with a family history of pneumonia and a personal history of otitis media. This combination of immunological findings and clinical history suggests an immune deficiency. Here is a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Common Variable Immunodeficiency (CVID): This condition is characterized by impaired B cell differentiation into plasma cells, leading to low antibody levels (including IgG), recurrent infections (such as pneumonia and otitis media), and a normal T cell count. The family history of pneumonia could suggest a genetic predisposition, which aligns with some forms of CVID.

• Other Likely Diagnoses

  • Selective IgG Subclass Deficiency: Patients with this condition have deficiencies in one or more subclasses of IgG, which can lead to recurrent infections, despite normal total IgG levels. However, given the patient's low IgG, this might be less likely but still worth considering.
  • IgA Deficiency: Although the question focuses on IgG, IgA deficiency is the most common primary immunodeficiency and can present with recurrent infections, particularly of the respiratory and gastrointestinal tracts. Some patients with IgA deficiency may also have low levels of other immunoglobulins.

• Do Not Miss Diagnoses

  • X-linked Agammaglobulinemia (XLA): Although less likely given the patient's age and the fact that XLA typically presents in infancy with severe infections, it's crucial not to miss this diagnosis. XLA is characterized by very low B cell counts and all classes of immunoglobulins are severely decreased.
  • Good’s Syndrome (Thymoma with Immunodeficiency): This rare condition involves a thymoma associated with immunodeficiency, characterized by low or absent B cells and inverted CD4/CD8 T cell ratio. It's essential to consider due to its potential for severe immunocompromise and the need for thymoma treatment.

• Rare Diagnoses

  • Hyper-IgM Syndrome: Typically characterized by elevated IgM levels with low IgG, IgA, and sometimes IgE, due to a defect in the CD40 ligand on T cells or other components of the CD40-CD40L interaction. The normal T cell count and low IgG without mention of elevated IgM make this less likely.
  • Wiskott-Aldrich Syndrome: An X-linked recessive disorder characterized by eczema, thrombocytopenia, and recurrent infections, due to mutations in the WAS gene affecting T lymphocyte and platelet function. The lack of specific mention of eczema or thrombocytopenia makes this diagnosis less likely based on the provided information.