What is the diagnosis breakdown for envenomation and bite injuries, including pathophysiology, physical examination findings, symptoms, first-line diagnostic tests, acute management, long-term management, red flags, potential complications, and common pitfalls in Family Medicine (Family Medicine) and Step 2 Clinical Knowledge (Step 2 CK)?

From the Guidelines

Sting and bite injuries should be managed with a focus on symptomatic treatment, including wound cleansing, pain control, and antihistamines for mild allergic reactions, with severe reactions requiring immediate epinephrine and supportive therapy. The pathophysiology of these injuries typically involves direct tissue trauma, toxin introduction, allergic reactions, or infection. Physical exam findings may include localized pain, erythema, swelling, puncture wounds, and potentially systemic symptoms like fever, nausea, or anaphylaxis in severe cases 1.

Diagnosis Breakdown

• Pathophysiology: direct tissue trauma, toxin introduction, allergic reactions, or infection
• Physical exam findings/symptoms: localized pain, erythema, swelling, puncture wounds, systemic symptoms like fever, nausea, or anaphylaxis
• First line test: thorough clinical examination, with additional testing based on specific concerns such as wound cultures for suspected infection or toxicology screens for certain venomous bites
• Acute management:
  • Wound cleansing with soap and water
  • Removing embedded stingers or foreign bodies
  • Tetanus prophylaxis if indicated
  • Pain control with acetaminophen or NSAIDs
  • Antihistamines for mild allergic reactions
  • Epinephrine (0.3-0.5mg IM for adults, 0.15mg for children) for severe reactions, as delayed administration of epinephrine has been associated with fatal sting reactions 1
• Long term management:
  • Wound care
  • Monitoring for infection
  • Completing antibiotic courses if prescribed (typically amoxicillin-clavulanate 875/125mg BID for 5-7 days for mammalian bites)
  • Follow-up for complicated wounds

Red Flags and Complications

• Red flags that alter management: signs of anaphylaxis, significant tissue necrosis, compartment syndrome, systemic toxicity, or infection spreading beyond the initial site
• Complications: secondary infection, tissue necrosis, scarring, post-inflammatory hyperpigmentation, and rarely sepsis or death
• Common pitfalls on exams: failing to recognize anaphylaxis requiring immediate epinephrine, overlooking the need for rabies prophylaxis in unprovoked mammalian bites, not considering prophylactic antibiotics for high-risk bites (especially hand wounds or cat bites), and missing the diagnosis of compartment syndrome requiring surgical consultation. Additionally, irrigation of human and animal bites with copious amounts of water is recommended 1.

It is essential to prioritize the management of sting and bite injuries based on the severity of the reaction and the presence of red flags, with a focus on preventing morbidity, mortality, and improving quality of life.

From the Research

Diagnosis Breakdown for Sting and Bite Injuries

Pathophysiology

• Insect venom induces a toxic reaction at the site of the sting, causing local and systemic reactions 2
• Anaphylaxis is a life-threatening systemic reaction, normally occurring within one to two hours of exposure to an allergen 3
• Mast cell degranulation plays a key role in the pathophysiology of anaphylaxis, with serum tryptase levels reflecting this process 3

Physical Exam Findings/Symptoms

• Urticaria, difficulty breathing, and mucosal swelling are the most common symptoms of anaphylaxis 3
• Local reactions can cause a wheal or papule, while large local reactions may ensue, but other diseases are rare 2
• Symptoms of anaphylaxis can manifest signs and symptoms related to the cutaneous, respiratory, cardiovascular, and gastrointestinal systems 4

First Line Test

• No specific first-line test is mentioned in the studies, but serum tryptase levels can be obtained when the clinical diagnosis of anaphylaxis is not clear 3

Acute Management

• Removal of the trigger and early administration of intramuscular epinephrine are crucial in the acute management of anaphylaxis 3, 4
• Supportive care for the patient's airway, breathing, and circulation, as well as a period of observation for potential biphasic reactions, are also important 3
• Antihistamines and corticosteroids can be considered as adjunct medications, but only after epinephrine administration 3, 4

Long Term Management

• Patients who have had a systemic reaction or a large local reaction due to insect allergy must take permanent measures to avoid further allergen contact, and to make sure they can treat themselves adequately if stung again 2
• Specific immunotherapy may be necessary for patients with systemic anaphylactic reactions to bee or wasp stings 2
• Developing an emergency action plan, referral to an allergist, and patient education on avoidance of triggers and appropriate use of an epinephrine auto-injector are also important 3

Red Flags that May Change Management

• Coexisting asthma, mast cell disorders, older age, underlying cardiovascular disease, peanut and tree nut allergy, and drug-induced reactions are associated with severe or fatal anaphylactic reactions 3
• Mastocytosis is found in 3% to 5% of patients with sting anaphylaxis, rendering these patients prone to very severe reactions 2

Complications

• Anaphylaxis can cause severe disease, with approximately 1500 patients dying annually in the United States from this deadly disorder 4
• Delayed epinephrine administration is a risk factor for fatal anaphylaxis 5

Common Pitfalls for Selecting the Wrong Answer

• Delaying epinephrine administration or replacing it with antihistamines or corticosteroids can be detrimental to patient outcomes 3, 4, 5
• Failing to recognize the severity of anaphylaxis or not providing adequate supportive care can also lead to poor outcomes 3, 4