Thank you for your recent inquiry.
Unfortunately, the best I can do for you to help you understand the differences between septic shock and anaphylactic shock is to refer you to references discussing each one. There are clearly distinct differences, but it would be impossible for me to discuss these in detail in this venue. Thus the task of contrasting them for you in great detail would be impossible to perform on this website, but I will do my best to outline for you some of the clearcut differences that apply, and refer you to more detailed sources where you would need to read separate chapters about each entity.
The cause of the differences between septic shock and anaphylactic shock relate to the provocative agents in each case. In anaphylactic shock, the provocative agent, as you know, is an allergen. In septic shock, the provocative agents are bacteria. In anaphylactic shock, the allergen binds to an antibody affixed to mast cells, and the mediators of the anaphylactic reaction are released from mast cells. The major mediator is probably histamine, but clearly other mediators are also involved. These consist of leukotrienes, prostaglandins, and platelet activating factor. In septic shock, the mediators are released from monocytes, neutrophils, and macrophages, and consist of interleukins and other inflammatory molecules such as tumor necrosis factor alpha. Interleukin 6 and interleukin 1 are also operative in the production of septic shock.
Because the mediators are entirely different from one another, the clinical manifestations vary between the two events. Cutaneous manifestations occur in the vast majority of anaphylactic episodes because the major mediator is histamine. These cutaneous manifestations are itching, urticaria, and flushing. These are not components of septic shock because of the difference in the mediators. In septic shock, there is fever, and usually either a very low white count (less than 4,000) or a very high white count (above 12,000). There is no fever in anaphylactic shock, and characteristically the white count is never low, and usually normal.
These differences also make response to various therapies different. For example, the drug of choice in anaphylactic shock is epinephrine; whereas epinephrine is not employed in septic shock unless there is failure to respond to more traditional vasoconstrictive agents such as dopamine and norepinephrine. In anaphylactic shock, antihistamines can be of help, but would be of no utility in septic shock since histamine is not a known mediator of this disorder. Fibrinolysis is far more common in septic shock than in anaphylactic shock. Therefore recombinant human activating protein C is employed in this disorder, but has not, to my knowledge, ever been employed to treat anaphylactic shock.
Once again, this is a brief and incomplete summary of the differences between these two disorders. I would therefore refer you to two references which would be of help to you for further understanding of the distinction between these two quite different disorders as far as their pathogenesis and etiology are concerned.
One reference is: Dellinger RP. Septic shock: treatment and medication, available on emedicine (from WebMD). The second reference is: Lieberman P. Anaphylaxis. In: Allergy: Principles and Practice, Edition 7, edited by Atkinson F, Bochner B, Busse W, Holgate S, Lemanske R, and Simons FER (Publisher Mosby, an affiliate of Elsevier, Inc.), 2009; 1027-1051.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.