HY lecture notes:
Recurrent varicella infections; what is the immunologic defect? –> answer = T cell dysfunction (defect in cell-mediated immunity).
T cell deficiency –> Q may mention absent thymic shadow.
B cell deficiency –> Q may say absent or scanty lymph nodes + tonsils.
Bruton X-linked agammaglobulinemia –> B cell deficiency –> bacterial infections only since ~6 months of age.
Severe combined immunodeficiency (SCID) –> X-linked (more common) or AR.
X-linked SCID = common gamma chain mutation, or IL-2 receptor deficiency.
AR SCID = adenosine deaminase deficiency.
SCID is classically all different types of infections (bacterial, viral, fungal, protozoal) from birth.
Note the contrast with Bruton.
However one of the Qs on a newer Peds form says “bacterial infections since birth” for a Bruton Q. This is “outrageous” because the timeframe has always been a classic means to distinguish Bruton from SCID, but we can’t argue with the NBME/USMLE. The key to this Q was that the infections were limited to bacterial, whereas in SCID, there will certainly be a variety of infections.
For Bruton, supply immunoglobulins to Tx. Bone marrow transplant is definitive. For SCID, must do bone marrow transplant.
Sometimes the answer for Bruton is “deficiency of humoral immunity.”
Chronic granulomatous disease (CGD; aka respiratory burst; aka NADPH oxidase deficiency) –> susceptibility to catalase (+) organisms –> SPACES
- Serratia/Staph, Pseudomonas, Actinomyces/Aspergillus, Candida, E. coli.
The bolded ones are ultra-HY as more specific for NADPH oxidase deficiency. In other words, if Q mentions Hx of Serratia sepsis, you’re likely dealing with CGD.
Dx with dihydrorhodamine test; tetrazolium blue assay is now obsolete and the WRONG answer. They have both answer choices on NBME 15 or 16 for Step 1 and dihydrorhodamine test is correct.
Newer CGD Qs on the peds forms are now giving recurrent Staph infections as the presentation.
IgA deficiency is probably the highest yield immunodeficiency for the 2CK and peds shelf.
Presentation is always recurrent sinopulmonary infections in a teenager or young adult. I will always tell students you can Dx this one because the presentation is “not that bad,” which means the vignette won’t give you a a young, sick kid as with the Bruton and SCID vignettes.
Usually a 16-35-year-old with Hx of a few pneumonias and/or several instances of sinusitis, treated with antibiotics. Patient now presents with sore cheeks (sinusitis).
Classic /easy Step 1 detail is Hx of anaphylaxis with blood transfusion, but for 2CK, you need to know IgA deficiency also presents with:
- Atopy (asthma, seasonal allergies, eczema).
- Giardia infection in the Hx
- Other autoimmune diseases (e.g., vitiligo).
- False (-) antibodies for Celiac screen, since anti-tissue transglutaminase, -gliadin/-endomysial are IgA.
Answer for IgA deficiency will be “defect in humoral immunity,” or “deficiency of mucosal immunoglobulin.” Note the former can be correct for either Bruton or IgA deficiency, but the latter would be wrong for Bruton.
