You’re doing a Q-bank block, you see an infant with eczema and “weird” bleeding, and your brain immediately goes to Wiskott-Aldrich. Perfect—except the question writers know that too. The real score comes from being able to defend why Wiskott-Aldrich is right and why each distractor is wrong based on the vignette’s details.
Tag: Immunology > Immunodeficiencies
The Clinical Vignette (Classic Q-Bank Style)
A 6-month-old boy has recurrent otitis media and pneumonia. He has eczema on his trunk and flexor surfaces. Parents report easy bruising and prolonged bleeding after circumcision. Exam shows petechiae. Labs reveal thrombocytopenia with small platelets. Immunoglobulins: low IgM, high IgA and IgE.
Most likely diagnosis? → Wiskott-Aldrich syndrome (WAS).
Why Wiskott-Aldrich Is the Correct Answer
The “Triad” You Must Recognize
Wiskott-Aldrich classically presents with:
- Eczema
- Recurrent infections (combined immunodeficiency)
- Thrombocytopenia with small platelets (microthrombocytes)
A quick way to remember is: WAS = Worse platelets (small) + Atopic dermatitis + Susceptibility to infections.
Pathophysiology That Explains the Whole Picture
- X-linked recessive
- Mutation in WAS gene → defective WASP (Wiskott-Aldrich syndrome protein)
- Leads to impaired actin cytoskeleton reorganization in leukocytes
- Poor T-cell activation and impaired immune synapse formation
- Abnormal platelet formation → small platelets and thrombocytopenia
Immunoglobulin Pattern (High Yield)
Typical pattern:
- ↓ IgM
- ↑ IgA and ↑ IgE
- IgG often normal or variable
USMLE-Level Complications
Patients are at increased risk for:
- Encapsulated organisms (due to humoral dysfunction)
- Autoimmune disease (immune dysregulation)
- Malignancy, especially lymphoma
Management (You Should Know This)
- Hematopoietic stem cell transplant is definitive
- Supportive:
- IVIG in some cases
- Antibiotic prophylaxis (case-dependent)
- Avoid platelet-affecting meds; manage bleeding risk
The Q-Bank Power Move: Why Each Distractor Is Wrong
Below are common answer choices that can look tempting if you anchor on one feature (like eczema or infections) and ignore the rest.
Distractor 1: Bruton's Agammaglobulinemia (X-linked agammaglobulinemia)
Why it’s tempting: recurrent bacterial/enteroviral infections in a boy.
Why it’s wrong here:
- Bruton's is a B-cell maturation defect (BTK mutation) → absent B cells and very low immunoglobulins across the board
- Presents after 6 months when maternal IgG wanes (that part overlaps), but:
- No eczema as a signature feature
- No thrombocytopenia
- Would expect absent tonsils/adenoids (lack of lymphoid tissue)
Key differentiator:
Bruton = no B cells, no immunoglobulins, no lymph nodes/tonsils.
WAS = eczema + small platelets + abnormal Ig pattern.
Distractor 2: Hyper-IgE Syndrome (Job syndrome)
Why it’s tempting: eczema-like dermatitis + recurrent infections + high IgE.
Why it’s wrong here: Hyper-IgE (STAT3 mutation → Th17 deficiency) features:
- Coarse facies
- Cold (noninflamed) staphylococcal abscesses
- Retained primary teeth
- Eczema
- ↑ IgE
But you should not see:
- Thrombocytopenia
- Small platelets
- The characteristic low IgM pattern
Key differentiator:
Job = “FATED” (coarse Facies, cold Abscesses, retained Teeth, ↑ E/IgE, Dermatologic problems).
WAS = bleeding + microthrombocytes.
Distractor 3: DiGeorge Syndrome (22q11 deletion)
Why it’s tempting: recurrent infections (T-cell dysfunction).
Why it’s wrong here: DiGeorge is thymic aplasia/hypoplasia → T-cell deficiency with:
- Hypocalcemia (↓ PTH) → tetany/seizures
- Conotruncal cardiac defects (truncus arteriosus, TOF)
- Absent thymic shadow
It does not classically cause:
- Eczema + thrombocytopenia with small platelets
- The WAS immunoglobulin pattern
Key differentiator:
DiGeorge = cardiac + calcium + thymus.
WAS = skin + platelets + infections.
Distractor 4: Chronic Granulomatous Disease (CGD)
Why it’s tempting: recurrent infections in a young child.
Why it’s wrong here: CGD is a phagocyte NADPH oxidase defect → decreased respiratory burst.
- Susceptible to catalase-positive organisms
- Often presents with recurrent pneumonia, lymphadenitis, skin infections, granulomas
But CGD does not explain:
- Thrombocytopenia with small platelets
- Classic eczema as a defining finding (CGD can have skin infections, but the triad isn’t there)
- The IgM low / IgA+IgE high pattern
Key differentiator:
CGD = catalase-positive infections + abnormal oxidative burst tests (DHR).
WAS = platelet size abnormality + eczema.
Distractor 5: Leukocyte Adhesion Deficiency (LAD)
Why it’s tempting: recurrent bacterial infections.
Why it’s wrong here: LAD (CD18 integrin defect) features:
- Delayed separation of umbilical cord
- No pus
- Impaired wound healing
- Neutrophilia (can’t exit bloodstream)
Not expected:
- Eczema triad
- Thrombocytopenia
- Small platelets
Key differentiator:
LAD = “No pus, no performance” + delayed cord separation.
WAS = microplatelets and bleeding.
Distractor 6: Severe Combined Immunodeficiency (SCID)
Why it’s tempting: severe/recurrent infections early in life.
Why it’s wrong here: SCID presents with:
- Severe infections (bacterial, viral, fungal, protozoal)
- Chronic diarrhea, failure to thrive
- Absent thymic shadow
- Low T cells (and often B/NK depending on type)
SCID doesn’t classically cause:
- Small platelets and thrombocytopenia
- Eczema + bleeding as the key combo (though chronic rashes/candidiasis can occur)
Key differentiator:
SCID = profound infections + absent thymus + severe FTT.
WAS = eczema + bleeding + infections with characteristic Ig changes.
High-Yield Table: Rapid Differentiation (USMLE Favorite)
| Disorder | Inheritance/Defect | Key Clues | Labs/Associations |
|---|---|---|---|
| Wiskott-Aldrich | XLR, WASP (actin cytoskeleton) | Eczema + recurrent infections + thrombocytopenia with small platelets | ↓ IgM, ↑ IgA/IgE, lymphoma risk |
| Bruton (XLA) | XLR, BTK (B cell maturation) | Recurrent bacterial/enteroviral infections after 6 months, absent tonsils | ↓ all Igs, ↓ B cells |
| DiGeorge | 22q11 deletion | Conotruncal defects, hypocalcemia, absent thymus | ↓ T cells |
| Hyper-IgE (Job) | STAT3, Th17 defect | Cold abscesses, coarse facies, retained teeth, eczema | ↑ IgE |
| CGD | NADPH oxidase | Catalase+ infections, granulomas | Abnormal DHR |
| LAD | CD18 integrin | Delayed cord separation, no pus, neutrophilia | Impaired adhesion/migration |
| SCID | IL-2Rγ (XLR) or ADA | Severe infections, diarrhea, FTT | ↓ T cells (± ↓ B/NK) |
Exam Strategy: How to “Lock In” Wiskott-Aldrich
When you see this combo, stop overthinking:
- Eczema (atopic dermatitis)
- Bleeding/petechiae with thrombocytopenia
- Platelets are small
- Recurrent infections + characteristic Ig pattern (↓ IgM, ↑ IgA/IgE)
If the stem includes small platelets, it’s basically the test writer highlighting the answer in bold.