Chief Complaint: Infections, Recurrent*
| Pivotal Assessment | Findings | ||
|---|---|---|---|
| History | Poor protein diet | ||
| Physical Exam | Pale streaks in hair and skin | ||
* pneumonia, meningitis, sepsis) caused by both common and opportunistic pathogens.
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Severe Combined Immunodeficiency (SCID) is a group of rare, inherited disorders characterized by severe abnormalities in both the cellular and humoral components of the immune system. It is often diagnosed in infancy due to the severe and recurrent infections the child may experience. Here's how SCID is typically diagnosed:
### 1. **Clinical Presentation**
- **Recurrent Infections:** Infants with SCID often have severe, recurrent infections (e.g., pneumonia, meningitis, sepsis) caused by both common and opportunistic pathogens.
- **Failure to Thrive:** Poor growth or development may be noticed due to frequent illnesses.
- **Chronic Diarrhea:** Persistent diarrhea is common.
- **Family History:** A family history of SCID or early deaths due to infections might raise suspicion.
### 2. **Laboratory Tests**
- **Complete Blood Count (CBC) with Differential:**
- **Lymphopenia:** A low lymphocyte count is a hallmark of SCID. In infants, a lymphocyte count below 3,000 cells/µL is concerning.
- **Flow Cytometry:**
- Used to analyze the different types of immune cells (T cells, B cells, NK cells). In SCID, T cells are usually profoundly decreased or absent, and B cells may be present but non-functional.
- **Immunoglobulin Levels:**
- Low or absent levels of immunoglobulins (IgG, IgA, IgM) due to the lack of functional B cells.
- **Newborn Screening:**
- Many countries now include SCID in newborn screening programs. The test measures T-cell receptor excision circles (TRECs), which are by-products of T-cell receptor gene rearrangement. Low TREC levels indicate a lack of functional T cells.
### 3. **Genetic Testing**
- **Molecular Diagnosis:**
- Genetic testing can identify mutations in the genes known to cause SCID (e.g., IL2RG, ADA, RAG1, RAG2). This confirms the diagnosis and can guide treatment, such as identifying suitable candidates for gene therapy or bone marrow transplantation.
### 4. **Additional Tests**
- **Delayed Hypersensitivity Skin Testing:**
- In older children, tests like the Mantoux test for tuberculosis may show anergy (lack of response), which is consistent with cellular immune deficiency.
- **Radiography:**
- Chest X-rays might show the absence of a thymic shadow, which is common in SCID due to the lack of a functional thymus gland.
### 5. **Consultation with an Immunologist**
- If SCID is suspected based on initial tests, referral to a pediatric immunologist is essential for further evaluation and management.
### 6. **Early Intervention**
- Early diagnosis is crucial for SCID as it allows for prompt treatment, which may include bone marrow transplantation, enzyme replacement therapy, or gene therapy. Without treatment, SCID is typically fatal in the first year of life.
### 7. **Confirmatory Testing:**
- Sometimes additional functional assays, such as the assessment of specific antibody responses to vaccines, may be needed to confirm the diagnosis.
SCID is a medical emergency. If suspected, it requires immediate action to prevent severe infections and improve the chances of survival.