# A nurse is assessing a 28-year-old patient with suspected primary immunodeficiency syndrome. Which assessment finding would be MOST indicative of a severe combined immunodeficiency (SCID)?

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## 문제

A nurse is assessing a 28-year-old patient with suspected primary immunodeficiency syndrome. Which assessment finding would be MOST indicative of a severe combined immunodeficiency (SCID)?

## 보기

1. Chronic diarrhea with weight loss and oral thrush
2. Absence of palpable lymph nodes and tonsils with severe lymphopenia **✔ 정답**
3. Recurrent upper respiratory infections with normal white blood cell count
4. Delayed wound healing with frequent skin infections

**정답: 2**

## 해설

Absence of palpable lymph nodes and tonsils with severe lymphopenia is pathognomonic for SCID, reflecting profound T- and B-cell deficiency. Other options (e.g., chronic diarrhea, recurrent infections) are common in immunodeficiencies but not specific to SCID.

## 심화 해설

Understanding Severe Combined Immunodeficiency (SCID)

Severe Combined Immunodeficiency (SCID) represents a group of life-threatening genetic disorders characterized by profound defects in both cellular (T-cell) and humoral (B-cell) immunity. The underlying pathophysiology involves mutations in genes critical for lymphocyte development and function. For instance, mutations in RAG1/2 (Recombination Activating Genes) prevent the essential V(D)J rearrangement of antigen receptors, blocking lymphocyte maturation at an early stage [1]. Similarly, defects in the IL2RG gene disrupt the common gamma chain shared by multiple interleukin receptors (IL-2, IL-4, IL-7, IL-9, IL-15, IL-21), which is pivotal for lymphocyte development and homeostasis [3]. The clinical consequence of these molecular defects is a near-complete absence of functional T and B lymphocytes, leaving the infant vulnerable to severe, persistent infections from the first months of life.

Analysis of Assessment Findings

In evaluating a patient for SCID, the nurse must differentiate between findings suggestive of a profound combined defect versus those indicating a more selective immunodeficiency or other condition.

- **Option 1: Chronic diarrhea with weight loss and oral thrush.** While these are common clinical manifestations of SCID resulting from opportunistic infections, they are not the most specific or pathognomonic finding. These symptoms can be present in various immunodeficient states, including less severe combined immunodeficiencies (CID) or isolated T-cell defects.

- **Option 2: Absence of palpable lymph nodes and tonsils with severe lymphopenia.** This is the hallmark physical and laboratory finding for classical SCID. The genetic mutations (e.g., in RAG1/2, IL2RG, or TRAC) lead to a developmental arrest of lymphocytes [1, 2, 3]. The resulting severe lymphopenia (a critically low absolute lymphocyte count, often

## 임상 시나리오

SCID Assessment: The Lymphoid ExamAbsence of lymph nodes and tonsils is a critical red flag
In a young infant with suspected immunodeficiency, a thorough physical exam is essential. The absence of palpable lymph nodes and absent tonsillar tissue are pathognomonic for Severe Combined Immunodeficiency (SCID). This finding directly reflects the profound deficiency of T and B lymphocytes needed to populate these organs.

This physical finding is more specific than common presenting symptoms like chronic diarrhea or oral thrush. It should be correlated with a complete blood count with differential. The lab hallmark is severe lymphopenia, typically with an absolute lymphocyte count (ALC) below 2,800 cells/µL in infancy, often significantly lower.

CautionDo not administer live vaccines (e.g., rotavirus, MMR, varicella) to any infant with suspected SCID. A lack of functional immunity can lead to fatal disseminated infection from the vaccine strain. Newborn screening for SCID using the TREC assay is now standard in many regions.

## 핵심 개념

- **Severe Combined Immunodeficiency (SCID)** — A life-threatening genetic disorder characterized by profound defects in both T-cell and B-cell immunity, leading to severe lymphopenia and absent lymphoid tissue.
- **Lymphopenia** — An abnormally low level of lymphocytes in the blood, a hallmark of SCID reflecting the combined deficiency of T and B cells.
- **Pathognomonic** — A sign or symptom that is so characteristic of a disease that it can be used to make a diagnosis.
- **V(D)J Recombination** — The process by which developing lymphocytes rearrange their DNA to generate a diverse repertoire of antigen receptors; mutations in genes like RAG1/2 block this process in SCID.

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