Regarding Anaphylaxis...

Regarding Anaphylaxis answer the following questions:
1. What is the clinical presentation in a typical case of anaphylaxis?
2. What is the underlying pathophysiologic process?
3. What conditions should be considered in the differential diagnosis?

Answers:


1. What is the clinical presentation in a typical case of anaphylaxis?
Answer: In the most severe cases, the clinical presentation consists of sudden hypotension with or without cutaneous signs, bronchospasm, or laryngeal obstruction. Patients occasionally report a “sense of impending doom.” This may occur within minutes of the ingestion of a specific food, injection of an antigen (e.g., an antibiotic), or an insect sting, and may be fatal.
A less rapid onset can begin w ith urticaria, angioedema, shortness of breath, hoarseness, and moderate hypotension.
If the offending substance has been ingested, there can be abdominal cramps, vomiting, and diarrhea. The diagnosis of anaphylaxis should be easily made if the symptoms described appear over the course of minutes up to an hour. The blood pressure need not drop—that is, there can be anaphylaxis without shock.

2. What is the underlying pathophysiologic process?
Answer: Mast cells and basophils are activated when an antigen (e.g., penicillin) combines with the antigen-combining site of immunoglobulin E (IgE) antibodies that are bound to FcεRI, the high affinity receptor for IgE.
Vasoactive mediators such as histamine, leukotriene C4 (LTC4), and prostaglandin D2 (PGD 2) rapidly enter the circulation. In some circumstances, mast cells are activated by non-IgE mechanisms, such as may be triggered by radio contrast dye injections or by non steroidal anti inflammatory drugs (NSAIDs); this is called an anaphylactoid reaction, but the basic physiologic characteristics and treatment are otherwise similar to those of IgE-mediated anaphylaxis.

3. What conditions should be considered in the differential diagnosis?
The differential diagnosis list is not long. Collapse due to septic shock, cardiac arrhythmia, or  asystole must be considered. The most common source of error is failing to recognize vasovagal. In such a situation, the patient's pulse is slow and there is no urticaria, edema, or dyspnea. The pulse is always rapid in the setting of anaphylaxis unless the patient is taking a β-adrenergic blocker or there is an underlying conduction defect. Patients with hyperventilation do not wheeze or have hypotension. How ever, determining the cause of the anaphylactic episode can be difficult because
antecedent events are not always clear and some episodes will remain idiopathic.