Patients may not present with all of the signs and symptoms or may have clinical findings in only a few of the organ systems. Consequently, there can be considerable overlap with other disease processes that require alternate treatment strategies. The differential should include the following: 

• Urticaria: this is a cutaneous reaction that leads to raised eruptions (hives) and well-circumscribed reddened areas with pale centers (wheel and flare). Patients will have associated pruritis (itchiness). 
• Angioedema: this presents quite similarly to urticaria and is similar pathogenesis. Vasoactive mediators cause dilation of subcutaneous arterioles, and the associated capillary leak leads to skin manifestation. The pathogenesis is superficial toe the dermis and causes well-circumscribed and non-pitting edema.
• Hereditary angioedema: in this case, the edema is in the gastrointestinal system leading to significant abdominal pain and increased mucosal edema of the pulmonary system causing respiratory distress. Patients should be treated using C1 esterase inhibition concentrate or, alternatively, fresh frozen plasma. 
• Severe asthma: the bronchospasm of anaphylaxis and asthma are quite similar; however, the two disease processes must be distinguished as treatment is very different. 
• Vocal cord dysfunction: this leads to a voice change or voice loss that can mimic pharyngeal angioedema.
• Scombroid poison: this is a foodborne illness that happens following the ingestion of rotten tuna mackerel, mahi-mahi. Patients will have symptoms in under 30 minutes, including headache, urticaria, nausea, emesis, and diarrhea. The reaction is secondary to bacterial histamine production. Treatment is with antihistamines. 
• Angiotensin-converting enzyme inhibitors (ACEI): ACEI can cause laryngeal edema. The time frame is variable and can be up to years following initial use.
• Panic attack/disorder: patients can develop functional stridor due to forced vocal cord closing.
• Vasovagal reaction: a vasovagal related syncopal event can lead to a pale or flushed appearance after the collapse.