A 39-year-old woman sees her physician because of acute onset of severe dyspnea. On physical examination, she is afebrile and has marked laryngeal stridor and severe airway obstruction. The medical history indicates that she has had similar episodes since childhood and episodes of colicky gastrointestinal pain. Her mother and her brother are similarly affected. There is no history of severe or recurrent infections. She does not have urticaria. Laboratory studies show normal WBC count, hematocrit, and platelet count. A deficiency in which of the following plasma components is most likely to produce these findings?
A 39-year-old woman sees her physician because of acute onset of severe dyspnea. On physical examination, she is afebrile and has marked laryngeal stridor and severe airway obstruction. The medical history indicates that she has had similar episodes since childhood and episodes of colicky gastrointestinal pain. Her mother and her brother are similarly affected. There is no history of severe or recurrent infections. She does not have urticaria. Laboratory studies show normal WBC count, hematocrit, and platelet count. A deficiency in which of the following plasma components is most likely to produce these findings?
💡 Explanation
## **Core Concept**
The patient's symptoms of acute onset severe dyspnea, marked laryngeal stridor, severe airway obstruction, and a history of similar episodes since childhood, along with a family history, suggest an inherited condition affecting the immune system or a specific plasma component. The absence of severe infections or urticaria helps to narrow down the differential diagnosis. This scenario points towards a condition related to **plasma component deficiency**, likely involving the complement system or a related pathway.
## **Why the Correct Answer is Right**
The clinical presentation of recurrent episodes of severe airway obstruction, laryngeal stridor, and gastrointestinal pain, coupled with a familial component, is highly suggestive of **Hereditary Angioedema (HAE)**. HAE is caused by a deficiency or dysfunction of **C1 inhibitor (C1-INH)**, a plasma protein that regulates the complement, coagulation, kinin, and fibrinolytic systems. C1-INH deficiency leads to overproduction of bradykinin, a potent vasodilator that increases vascular permeability, resulting in the characteristic angioedema. The condition often presents in childhood and can affect various systems, including the skin, respiratory tract, and gastrointestinal tract.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not directly relate to the described condition of Hereditary Angioedema or a known plasma component deficiency leading to similar symptoms.
- **Option B:** This option is incorrect as it does not specify a known plasma component deficiency associated with the patient's symptoms.
- **Option D:** This option is incorrect because it does not correspond to a plasma component deficiency that would cause the described clinical picture.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in this case is that **Hereditary Angioedema** can present with life-threatening airway obstruction and is often misdiagnosed as allergic reactions or infections. Recognizing the familial component and the specific symptoms of angioedema without urticaria or significant infections is crucial. Also, note that **C1-INH deficiency** can be due to quantitative (Type I) or qualitative (Type II) defects, both leading to similar clinical manifestations.
## **Correct Answer:** .
✓ Correct Answer: B. C1 inhibitor
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