🩺 OBSERVED/INTERACTIVE STATION · CPSP FORMAT · 7 MINUTES · COLD URTICARIA + POLAR PLUNGE ANAPHYLAXIS
🧊 Observed Station – “December hives after walking home, plus peanut butter candy”
👧🏻 Clinical Scenario (TOACS – read / display):
A 12-year-old girl presents in December with hives and facial/hand swelling after walking home from the bus stop (cold exposure). Mother is worried because she ate a peanut butter candy on the bus. No prior food allergy diagnosis. She feels itchy but denies abdominal pain, nausea, chest tightness, or lightheadedness. Key history: On-and-off hives for 3 years, mostly winter. Last year, after “polar plunge” into a partially frozen lake, she developed full body hives, wheezing, and hypotension – required epinephrine in ED. Family was told to see an allergist but never followed up.
Task (observed): Identify the likely diagnosis, perform/discuss the ice cube test, differentiate from food allergy, and formulate immediate & long-term management.
🧊 Ice cube test (diagnostic): Place an ice cube in a plastic bag on volar forearm for 5 minutes. Remove and observe after 10 minutes. Positive = localized wheal/urticaria at site (cold-induced urticaria). Demonstrate or verbalize to examiner.
⚠️ Critical clue: Symptoms triggered by cold exposure (winter, polar plunge) + hives + prior anaphylaxis with hypotension/wheezing = acquired cold urticaria with risk of life-threatening reactions during swimming/cold water immersion. Peanut ingestion is likely a red herring; no history of peanut allergy & symptoms not temporally linked to candy alone.
💡 Examiner prompt: “The mother is convinced it’s peanut allergy. How do you differentiate? What test confirms cold urticaria? What is the risk of cold water anaphylaxis?”
🗨️ Examiner Q&A · Cold urticaria & Anaphylaxis
❓ Q1 (Examiner): “What is the most likely diagnosis in this girl? Justify.”
✅ Acquired cold urticaria (primary cold contact urticaria). Justification: recurrent winter hives, symptoms consistently after cold exposure (walking home in December, polar plunge), prior anaphylaxis during ice-water immersion. Peanut ingestion incidental; no classic IgE-mediated food allergy symptoms (no immediate reaction after candy alone).
❓ Q2 (Examiner): “Describe the ice cube test – procedure, interpretation, pitfalls.”
✅ Apply ice cube in a plastic bag (to avoid direct wetness) on volar forearm for 5 minutes. After removal, read at 10 minutes. Positive: pruritic, well-demarcated wheal/flare. Negative test does not completely exclude atypical cold urticaria (e.g., delayed or cold-dependent dermatographism). Test should be performed after antihistamines washout.
❓ Q3 (Examiner): “What distinguishes cold urticaria from other physical urticarias?”
✅ Cold urticaria: wheals after cold air/water/objects. Cholinergic urticaria: small pinpoint papules with exercise/hot showers/sweating. Dermographism: linear wheals after stroking. Delayed pressure urticaria: swelling hours after pressure. Cold-induced anaphylaxis is distinctive (can occur during swimming).
❓ Q4 (Examiner): “Could this be peanut allergy? How to rule out?”
✅ Unlikely: symptoms occur repeatedly in winter without peanut exposure. Peanut allergy typically causes immediate reaction (minutes to 2h) with urticaria, vomiting, or anaphylaxis after ingestion. Diagnostic approach: serum peanut-specific IgE, skin prick test, or oral food challenge if history equivocal. Negative test excludes peanut.
❓ Q5 (Examiner): “What additional workup is indicated in a child with cold urticaria?”
✅ CBC with differential, ESR/CRP, cryoglobulins, cryofibrinogen, cold agglutinins, serum protein electrophoresis, complement levels (C4, CH50). Rule out underlying infections (mononucleosis, hepatitis), autoimmune disease, or hematologic disorders. Most pediatric cases are idiopathic but secondary causes need exclusion.
❓ Q6 (Examiner): “Why is the polar plunge episode so significant? What is the risk?”
✅ Total body cold exposure (swimming, polar plunge) can cause massive mast cell degranulation → cold-induced anaphylaxis with hypotension, airway compromise, loss of consciousness, and even drowning. High mortality risk if epinephrine delayed. This patient already had wheezing/hypotension, placing her at high risk for recurrence.
❓ Q7 (Examiner): “What is first-line treatment for an acute cold urticaria flare with mild hives?”
✅ Nonsedating H1 antihistamines (cetirizine, loratadine, fexofenadine). For acute anaphylaxis (wheezing/hypotension): epinephrine IM 0.01 mg/kg (max 0.3 mg). Adjunct: cold avoidance, warm rewarming, and antihistamines for pruritus.
❓ Q8 (Examiner): “Should this child be prescribed an epinephrine autoinjector? Why?”
✅ Absolutely yes. She has a history of cold-induced anaphylaxis (hypotension, wheezing). She is at risk for future severe reactions with accidental cold exposure (swimming, winter sports). Prescribe epinephrine autoinjector (0.3 mg if weight ≥25 kg) and create an emergency action plan.
❓ Q9 (Examiner): “What preventive measures do you advise for cold urticaria?”
✅ Avoid sudden cold exposure, cold drinks, ice cream, swimming in cold water (risk of drowning). Wear warm layered clothing, gloves, face mask in winter. Premedicate with antihistamines before predictable cold exposure. Inform school about cold-induced anaphylaxis. Never swim alone.
❓ Q10 (Examiner): “What is the natural history of acquired cold urticaria in children?”
✅ Spontaneous resolution occurs in ~50% of children within 5-10 years. Median duration ~5-7 years. However, severe anaphylactic reactors may have more persistent disease. Antihistamines control symptoms, but avoidance remains cornerstone.
❓ Q11 (Examiner): “What is the role of omalizumab or other biologics in cold urticaria?”
✅ For severe, refractory cold urticaria unresponsive to high-dose antihistamines, omalizumab (anti-IgE) has shown efficacy in case series and trials. Other options: cyclosporine, montelukast (less evidence). Not first-line; refer to allergy specialist.
❓ Q12 (Examiner): “How do you differentiate familial cold autoinflammatory syndrome (FCAS) from this case?”
✅ FCAS (NLRP3 mutation) presents with urticaria-like rash, fever, arthralgia, conjunctivitis after cold exposure – NOT true urticaria (more maculopapular), associated with systemic inflammation, usually autosomal dominant, onset in infancy. Ice cube test negative. Our patient has typical wheals, anaphylaxis, negative family history → acquired cold urticaria.
🗣️ Examiner probing: “What if the ice cube test is negative but history strongly suggestive?” → Atypical cold urticaria (delayed, localized, or cold-dependent dermographism). Perform cold challenge with cold water immersion of hand (10°C for 5 min). “Can cold urticaria be secondary to infection?” → Yes, post-viral (EBV, hepatitis, mycoplasma).
🚨 Epinephrine autoinjector Mandatory for any patient with prior cold-induced anaphylaxis (hypotension, wheezing, laryngeal edema). Also consider for generalized hives with risk of aquatic activities.
⭐ High-yield for TOACS (cold anaphylaxis vs food allergy):
✔ Always ask about cold, exercise, water exposure in recurrent urticaria.
✔ Ice cube test = quick bedside diagnostic.
✔ Do not dismiss as “peanut allergy” without evidence; perform allergy testing to confirm.
✔ Prescribe epinephrine + educate on cold water dangers (drowning risk).
✔ Refer to allergy for possible omalizumab if refractory.
🎭 Observed Station – Candidate Tasks & Examiner Checklist
🩺 Candidate must demonstrate:
1️⃣ Introduce self, obtain consent, take focused history (cold exposure, polar plunge details, temporal relation to peanuts).
2️⃣ Perform general physical examination – note urticaria, angioedema; assess airway/breathing/circulation.
3️⃣ Perform (or verbalize) ice cube test – explain indication and interpretation to mother.
4️⃣ Differentiate between cold urticaria and food allergy – order peanut sIgE/skin test to rule out.
5️⃣ Prescribe epinephrine autoinjector (0.3 mg) and provide written anaphylaxis action plan.
6️⃣ Educate family: avoid cold water swimming, always carry epinephrine, premedicate with antihistamines before cold exposure, inform school.
7️⃣ Arrange allergy follow-up for possible secondary workup (cryoglobulins, complement) and immunotherapy (omalizumab if severe).
✅ Refers to allergist for possible omalizumab / long-term management
✅ Addresses maternal anxiety about peanut allergy with evidence-based reasoning
💬 Role-play script excerpt (candidate to mother):
“I understand you’re worried about the peanut candy, but her hives happen only in cold weather, even without peanuts. The polar plunge reaction with wheezing and low blood pressure tells us cold can cause severe allergic reactions. We will test for peanut allergy to be sure, but I strongly suspect cold urticaria. She needs an epinephrine injector and must avoid swimming in cold water or sudden cold exposure. Let me show you the ice cube test.”
📚 Reference (Nelson Textbook of Pediatrics, Chapter 189 – Urticaria and Angioedema, Physical urticarias):
Cold urticaria accounts for 1-3% of physical urticarias. Ice cube test sensitivity ~90%. High risk of anaphylaxis during swimming. Antihistamines + epinephrine autoinjector + avoidance = standard of care.