Missed diagnosis in anaphylaxis

It's largely due to non-textbook presentations according to this paper:

..the pathophysiology of anaphylaxis may cause patients to have symptoms that are consistent with anaphylaxis at the start of the reaction but may not be identified as such when seen later in the ED.

In addition, because anaphylaxis has such a wide range of possible symptoms, its differential diagnosis is lengthy and includes conditions such as asthma, vocal cord dysfunction, acute coronary syndrome (ACS), hereditary angioedema, vasovagal episode, and panic attack.5, 16 Atypical presentations make diagnosis particularly challenging.5 For example, acute airway obstruction during an anaphylactic event has sometimes been mislabeled as a “foreign body” in the airway. Vocal cord dysfunction also may present with a sensation of throat swelling and can be challenging to differentiate clinically from anaphylaxis, though fiberoptic laryngoscopy (if available) will determine whether swelling actually is present.

Exercise-induced anaphylaxis has been known to present as syncope and should be considered as part of the differential diagnosis in appropriate circumstances.5 Cardiac manifestations of anaphylaxis may mimic the symptoms of ACS, including arrhythmias in some cases, and this, in particular, takes time and effort to differentiate. Anaphylaxis can be especially low on the list of considerations when symptoms mimic ACS. Other conditions that may mimic anaphylaxis symptoms include flush syndromes (eg, carcinoid or disulfiram reactions), “restaurant syndromes” (eg, reactions to monosodium glutamate, sulfites, or scombroid), autonomic epilepsy, and vasomotor rhinitis. Additionally, anaphylaxis can sometimes cause nonspecific symptoms such as confusion, nausea, and dyspnea, which might be misattributed to more common conditions.