Case 14

Published on 18/02/2015 by admin

Filed under Allergy and Immunology

Last modified 18/02/2015

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CASE 14

Josh is a 19-year-old man who has been rushed to your emergency department from a local Italian restaurant, where he had become acutely “ill” while eating. On arrival he is pale, cool, and clammy and has a low blood pressure. There is no medic-alert bracelet to be seen. Putting your stethoscope to his chest you find he has wheezes throughout his lung fields but very poor air intake. A friend who is with him says this has never happened before, and, to his knowledge, no one in Josh’s family has ever been like this. What are your thoughts on how to proceed?

QUESTIONS FOR GROUP DISCUSSION

1. Describe specific conditions/circumstances that could lead to vasodilation and the patient’s symptoms as described.
2. Someone who is pale, cool, and clammy is not perfusing his peripheral tissue with blood. Explain how/why this happens in (a) trauma cases and (b) immunologic reactions in which biologic vasodilators are released.
3. Explain why vasodilatation is followed by sweating.
4. A deficiency in one of the complement regulatory proteins might present in this spontaneous manner. Name the protein and explain why a deficiency would lead to the symptoms observed.
5. Shellfish and nuts are two of the most potent mediators of food allergies. However, reactions as described in this case depend on re-exposure to a previously sensitized individual. Explain.
6. Ingestion of shellfish/nuts in a previously sensitized individual can lead to anaphylactic shock. There are a number of drugs you need to consider giving at this time, each acting in a slightly different manner and with different times of onset. What are they? Describe their mode of action and how long it takes for the effect to take place.
7. Note that food allergies will often present as nausea, stomach cramps, and diarrhea. Explain.
8. How would you determine the immediate precipitant of this reaction?
9. Individuals with allergies to shellfish/nuts and insect stings should carry three things. List these and provide a rationale for each.
10. Many allergic reactions are inconvenient but not life threatening. How do these types of allergic reactions manifest clinically?

RECOMMENDED APPROACH

Implications/Analysis of Family History

Other than the fact that his friend is unaware of any other family member presenting with similar conditions, we have no information regarding family history. A first time presentation in a 19-year-old, with no apparent family history, suggests that an inherited immune defect is unlikely (e.g., anaphylatoxins of the complement cascade). The absence of the medic-alert bracelet signifies that this is not a condition that has been previously diagnosed.

Implications/Analysis of Clinical History

Pale, cool, and clammy are the cardinal signs of impending shock and indicate that the patient is not perfusing the peripheral tissues with blood, hence pale and cool skin. A number of conditions can induce these symptoms, particularly blood loss during trauma, as the peripheral vasculature constricts to conserve remaining blood flow to the central key organs (e.g., brain/heart). However, even in the absence of severe blood loss, release of inflammatory mediators that induce vasodilatation and increase vascular (capillary) permeability can lead to a reduction in blood volume and cessation of blood flow to the periphery, with a concomitant drop in blood pressure (see Etiology). The low blood pressure triggers an increase in sympathetic nervous system activity and release of catecholamines from the adrenal medulla.

A number of nontrauma conditions can manifest in this manner. For example, patients experiencing septic shock as a result of gram-negative bacterial infection, dehydration, or heart damage may also present with similar symptoms. Josh’s illness, however, occurred suddenly while eating at an Italian restaurant, and this should steer us away from these causes. The acute presentation of Josh’s symptoms while eating is a strong indication that something this patient ate is most likely the precipitating factor. Ingested toxins (poisons) or a protein to which Josh had been previously sensitized are both in the realm of possibilities because these stimuli can induce the observed clinical “picture.”

Italian restaurants (and other exotic restaurants) are environments where nuts and shellfish are commonly on the menu. These are two of the most potent mediators of food allergies. Reaction depends on re-exposure of a previously sensitized individual, so your patient must have (at least once) eaten similar foods without a response (see Etiology). Drug or food allergies present like this more commonly than do toxins or poisons.

In addition to the signs of impending shock, Josh is wheezing and has poor air intake, suggesting the bronchi and bronchioles of the respiratory “tree” are constricting, which is consistent with an allergen-induced anaphylaxis.

Implications/Analysis of Laboratory Investigation

Up to this point, no laboratory tests have been requested, first, because we have been dealing with a life-threatening situation, and, second, because this is essentially a clinical diagnosis (made based on history and physical examination).

Additional Laboratory Tests

In situ/vivo Tests

At some stage you need to try to figure out the immediate precipitant of this reaction, with a focus on food allergies. In general, patients with suspected food allergies are screened with “skin prick tests.” In this test, a result is interpreted as positive if the allergen used to prick the skin leads to the formation of a wheal that is 3 mm (or greater) than that produced by the control substance. For this test, and any other “in vivo

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