Types of host defense defects predisposing to bacterial meningitis:
(1) deficiency immunoglobulins (B cell function) – Bruton (X-linked) agammaglobulinemia, common variable immunodeficiency, X-linked hypogammaglobulinemia with elevated IgM, acquired hypogammaglobulinemia
(2) combined B and T cell immunodeficiency – severe combined immunodeficiency, Wiskott-Aldrich syndrome, immunodeficiency with ataxia and telangiectasia, immunodeficiency with adenosine deaminase or nucleoside phosphorylase deficiency
(3) complement pathway defects – early complement deficiencies (C1, C2, C3), late complement deficiencies (C4, C5, C6, C7, C8, C9), alternative pathway (properdin)
(4) splenic dysfunction – after splenectomy, autosplenectomy (sickle cell disease), congenital asplenia
Some Rules for Patient Evaluation
No workup is required if all of the following are present:
(1) the patient was previously healthy
(2) no history of recurrent infection
(3) no risk factors for HIV disease
(4) not meningococcal disease
If meningococcal disease or disseminated gonococcal infection, consider:
(1) CH50 as screening test
(2) measurement of late complement pathway proteins (C4 – C9) and properdin if suspect defective host response
If adult < 50 years of age with pneumococcal or Listeria meningitis, then screen for HIV disease.
If there is a history of recurrent invasive bacterial infections, or if a single infection occurs in a child earlier (less than 6 months) or later (age 3-4 years) than usual:
(1) measure levels of IgG, IgM, IgE and IgA
(2) CH50 as screening test for complement pathway
(3) HIV testing if risk factors in parents
Reflex testing:
(1) If the patient shows reduced immunoglobulins, then B cells should be evaluated.
(2) If IgA is reduced look for deficiency in IgG subtypes (IgG2 or IgG4).
(3) If IgE is elevated, consider Wiskott-Aldrich syndrome.
(4) measurement of complement proteins and properdin if suspect defective host response, especially after infection with an encapsulated organism
To investigate splenic function:
(1) examine a blood smear for Howell-Jolly bodies
(2) consider radionuclide scan of the spleen and accessory spleens
The presence of thrombocytopenia and abnormally small platelets may indicate Wiskott-Aldrich syndrome.
