Immune System

Urticaria: acute and chronic management

Clinical Overview and When to Suspect Urticaria

— Individual wheals are migratory and resolve within <24 hours without bruising or scarring

— May coexist with angioedema (deeper dermal/subcutaneous swelling) in ~40% of cases

— Acute urticaria: symptoms <6 weeks; often triggered (viral URI in adults and children, foods, drugs, insect stings, contact)

— Chronic urticaria: daily or near-daily hives ≥6 weeks; subdivided into chronic spontaneous urticaria (CSU) and chronic inducible urticaria (CIndU) — dermatographism, cold, cholinergic, pressure, solar, aquagenic

— IgE-mediated (type I) — foods, drugs, latex, stings

— Non–IgE direct mast cell activation — opiates, vancomycin (red man), radiocontrast, NSAIDs

— Bradykinin-mediated angioedema (ACE inhibitor, hereditary C1 inhibitor deficiency) is not urticarial — no wheals, no pruritus

— Patient describes "blotchy, itchy welts that come and go," worse at night, individual lesions fade within hours

— New medication, recent viral illness, or stress

— Concern for anaphylaxis if hives + wheezing, hypotension, throat tightness, or GI symptoms

Board pearl: If a single wheal lasts >24 hours, is painful or burning rather than pruritic, or leaves purpura/hyperpigmentation, suspect urticarial vasculitis and biopsy — this changes management entirely toward immunosuppression and systemic workup.

Definition: Urticaria = transient, pruritic, erythematous wheals (hives) caused by mast cell degranulation in the superficial dermis, with histamine, leukotrienes, and prostaglandins driving vasodilation and plasma extravasation

Classification by duration (key Step 3 fork):

Epidemiology: Lifetime prevalence ~20%; CSU peaks in women age 20–40; strong association with autoimmune thyroid disease (Hashimoto)

Pathophysiology highlights:

When to suspect in the ambulatory clinic:

Presentation Patterns and Key History

— Sudden eruption of pruritic wheals within minutes to hours of exposure

— Triggers in adults: NSAIDs, antibiotics (β-lactams, sulfa), IV contrast, foods (shellfish, peanut, tree nut, egg), stings

— In children: viral infection is the #1 cause — often misattributed to amoxicillin given for the URI

— Wheals most days for ≥6 weeks with no identifiable external trigger in ~80–90%

— Often worse in evening, disrupts sleep, impairs quality of life comparable to ischemic heart disease on validated scales

— Ask about thyroid symptoms, autoimmune family history, recent H. pylori dyspepsia

— Dermatographism: linear wheals along scratch marks, tight clothing waistbands

— Cold urticaria: swimming in cold water, ice cream — risk of systemic anaphylaxis with full-body cold exposure (cold-water swimming death)

— Cholinergic: small 1–3 mm wheals with exercise, hot showers, anxiety; rises with core temperature, not friction

— Delayed pressure urticaria: deep painful swelling 4–6 hours after sustained pressure (purse strap, prolonged sitting)

— Solar: within minutes of UV exposure, spares chronically sun-exposed skin (face)

— Fever, arthralgia, weight loss → vasculitis, autoinflammatory syndromes (Schnitzler, cryopyrin-associated periodic syndromes)

— Lip/tongue swelling without hives on ACEi → bradykinin angioedema, stop the ACEi

— Postprandial diarrhea + flushing + hives → consider systemic mastocytosis (check tryptase)

Key distinction: Hives that are itchy and blanch = histaminergic; painful, non-pruritic, non-blanching swelling = bradykinin-mediated angioedema — antihistamines and epinephrine won't fully reverse the latter; use icatibant or C1-INH concentrate for HAE attacks.

Acute urticaria classic stem:

Chronic spontaneous urticaria (CSU):

Chronic inducible urticaria — targeted history:

Red-flag history elements:

Physical Exam Findings (and Hemodynamic Assessment when relevant)

— Wheals: raised, erythematous or porcelain-white, well-demarcated, polymorphic — round, annular, polycyclic, or geographic

— Blanch with pressure (diascopy) — confirms vasodilation, not purpura

— Mark the borders with a pen at the visit; lesions still present in the same location >24 hours later argue against simple urticaria and toward urticarial vasculitis

— Dermatographism: stroke the forearm firmly with a tongue depressor; a linear wheal in 1–3 minutes = positive

— Asymmetric, non-pitting, non-pruritic swelling of lips, periorbital tissue, tongue, hands, feet, genitals

— Bowel wall angioedema (HAE, ACEi) → colicky abdominal pain, sometimes mistaken for surgical abdomen

— Airway: stridor, hoarseness, drooling, tongue edema

— Breathing: wheeze, hypoxia, accessory muscle use

— Circulation: tachycardia, hypotension (SBP <90 or >30% drop from baseline), delayed cap refill

— GI: cramping, vomiting, diarrhea

— Anaphylaxis = involvement of ≥2 organ systems OR hypotension after exposure → IM epinephrine 0.3–0.5 mg (1:1000) into anterolateral thigh, repeat q5–15 min

— Goiter, periorbital edema → autoimmune thyroid

— Joint swelling, livedo → urticarial vasculitis, lupus

— Hepatosplenomegaly, telangiectasia macularis eruptiva perstans → mastocytosis

— Lymphadenopathy + recurrent fever → Schnitzler (monoclonal IgM)

CCS pearl: In a CCS case with hives + hypotension + wheeze, your first order is IM epinephrine, then IV access, IV fluids, supine with legs elevated, oxygen, H1 and H2 antihistamines, and methylprednisolone — diphenhydramine alone is never sufficient and giving it first is a board trap.

Skin exam:

Angioedema findings:

Anaphylaxis assessment — the critical bedside step:

Systemic clues to underlying disease:

Diagnostic Workup — Initial Labs / Imaging / ECG / Biomarkers

— History and exam alone establish diagnosis

— Avoid shotgun allergy panels and broad IgE testing in the absence of a specific suspected trigger — low pretest probability, high false-positive rate, and risk of unnecessary avoidance

— Step 3 ambulatory wisdom: targeted skin prick or specific IgE only when a temporally linked trigger is suspected (e.g., food eaten within 1–2 h, drug exposure)

— CBC with differential (eosinophilia → parasitic or drug; basopenia correlates with autoimmune CSU)

— CRP or ESR (elevation suggests urticarial vasculitis or autoinflammatory disease, not simple CSU)

— TSH ± anti-TPO antibodies — autoimmune thyroid present in ~10–15%

— Consider total IgE (predicts omalizumab response if elevated)

— Fever, arthralgia, elevated ESR → C3, C4, ANA, skin biopsy for urticarial vasculitis

— GI symptoms + flushing → serum tryptase (baseline); >20 ng/mL or persistent elevation → mastocytosis workup

— Recurrent angioedema without urticaria → C4 (low), C1 esterase inhibitor level and function, C1q — diagnose HAE types I/II vs acquired

— Recurrent fevers + bone pain + monoclonal IgM → Schnitzler syndrome

— Ice cube test (5 min on forearm) for cold urticaria

— FricTest or stroking for dermatographism

— Exercise challenge or warm bath for cholinergic

— Pressure test with weighted strap for delayed pressure

Board pearl: Routine testing for H. pylori, food allergy panels, ANA, and stool ova/parasites in unselected CSU is low yield and not recommended — order only when history suggests a specific etiology. This is a common Step 3 over-testing trap.

Acute urticaria — typically NO testing required:

Chronic spontaneous urticaria — minimal evidence-based workup per AAAAI/EAACI:

When to expand testing — symptom- or sign-driven only:

Provocation testing for inducible urticaria:

Diagnostic Workup — Advanced or Confirmatory Studies

— Intradermal injection of patient's own serum producing a wheal suggests functional autoantibodies against FcεRI or IgE — identifies autoimmune CSU subtype

— Predicts more severe disease and slower response to antihistamines; supports earlier escalation to omalizumab

— Individual wheals lasting >24 hours, painful/burning, residual hyperpigmentation, purpura

— Concern for urticarial vasculitis (leukocytoclastic vasculitis on histology) → check C3, C4, ANA, anti-C1q, hepatitis serologies, SPEP

— Histology in CSU shows perivascular lymphocytic infiltrate without vessel wall damage

— Type I (85%): low C4, low C1-INH level and function

— Type II (15%): low C4, normal C1-INH level but low C1-INH function

— Acquired (associated with lymphoproliferative disorder): low C4, low C1-INH, low C1q (distinguishes from hereditary)

— Confirm with repeat testing; screen first-degree relatives in HAE

— Serum tryptase persistently >20 ng/mL → bone marrow biopsy for KIT D816V mutation, CD25+ mast cells

— 24-hour urinary N-methylhistamine, prostaglandin metabolites

— UAS7 (Urticaria Activity Score, 7-day): scores wheals and pruritus; guides treatment escalation

— UCT (Urticaria Control Test): score ≥12 = well-controlled

— DLQI for quality-of-life impact

Step 3 management: Document a baseline UAS7 and UCT before starting therapy and reassess at 2–4 weeks — payer prior authorization for omalizumab in chronic urticaria typically requires documented failure of high-dose H1 antihistamines with objective scoring evidence.

Autologous serum skin test (ASST):

Skin biopsy — indications:

Hereditary angioedema confirmation:

Mastocytosis workup:

Disease-activity instruments (use at every CSU visit):

Risk Stratification or First-Line Management Logic

— Anaphylaxis present? → IM epinephrine, ED transfer, observation 4–6 h, epinephrine auto-injector prescription, allergy referral

— Angioedema of airway? → ED, secure airway early; if on ACEi, stop permanently and counsel that switch to ARB is generally acceptable but carries small residual risk

— Isolated cutaneous urticaria, stable? → outpatient stepwise therapy

— Step 1: Standard-dose second-generation H1 antihistamine daily (cetirizine 10 mg, loratadine 10 mg, fexofenadine 180 mg, levocetirizine 5 mg, desloratadine 5 mg, bilastine)

— Step 2: Updose the same second-generation antihistamine up to 4× standard dose (e.g., cetirizine 10 mg QID) — preferred over adding multiple agents

— Step 3: Add omalizumab 300 mg SC q4 weeks

— Step 4: Add cyclosporine (3–5 mg/kg/day) for refractory disease; consult allergy/immunology

— First-generation antihistamines (hydroxyzine, diphenhydramine) as scheduled therapy — sedation, anticholinergic burden, Beers list in elderly

— Chronic systemic corticosteroids — toxicity outweighs benefit; reserve short bursts (≤10 days, prednisone 0.5 mg/kg/day) for severe flares

— Leukotriene receptor antagonists — modest evidence; montelukast carries FDA black-box neuropsychiatric warning

— Avoid NSAIDs, alcohol, opiates, tight clothing, overheating, known specific triggers

— Acetaminophen is preferred analgesic

Board pearl: The single most common Step 3 wrong answer in CSU is "add another antihistamine" or "start prednisone taper" — the correct next step after standard-dose failure is updosing the same second-generation H1 antihistamine up to 4× before adding anything else.

Triage decision tree at the index visit:

EAACI/GA²LEN/WAO/AAAAI 4-step algorithm for CSU (memorize for boards):

Avoid as routine therapy:

Trigger mitigation counseling:

Pharmacotherapy — First-Line Drug Regimen

— Cetirizine 10 mg PO daily — most studied, mild sedation possible at high doses

— Levocetirizine 5 mg daily — active enantiomer, similar profile

— Fexofenadine 180 mg daily — least sedating, no QT issues at therapeutic doses

— Loratadine 10 mg daily, desloratadine 5 mg daily

— Bilastine 20 mg daily — non-sedating, no hepatic metabolism, good in renal impairment up to severe

— Updose to 2–4× daily dosing as a single agent before adding others — strong guideline recommendation

— Famotidine 20 mg BID — modest synergy; ranitidine withdrawn from US market (NDMA)

— Cimetidine retains use but has many CYP interactions

— Prednisone 40 mg daily ×5–7 days, no taper needed for short courses

— Avoid chronic use; rebound flares common on rapid withdrawal

— Hydroxyzine 25 mg PO at bedtime for severe nocturnal pruritus short-term

— Diphenhydramine 25–50 mg IV in acute ED settings as adjunct to epinephrine

— Avoid in elderly (Beers criteria), pregnancy first trimester, drivers, and patients on other sedatives

— 10–25 mg at bedtime for refractory pruritus; monitor QT, anticholinergic burden, interactions with MAOIs

— Montelukast 10 mg daily (NSAID/aspirin-exacerbated urticaria subtype may benefit)

— Vitamin D supplementation if deficient

Key distinction: Second-generation antihistamines at high dose are first-line for chronic urticaria; IM epinephrine is first-line for anaphylaxis — never substitute antihistamines for epinephrine in systemic reactions, even if the patient "only has hives."

Second-generation H1 antihistamines (cornerstone):

H2 antihistamines as add-on:

Short-burst systemic corticosteroids — severe acute flare only:

First-generation antihistamines — limited role:

Doxepin (tricyclic with potent H1/H2 blockade):

Adjuncts with limited evidence:

Procedures / Revascularization / Invasive Management (Biologics and Immunosuppression Expansion)

— 300 mg SC every 4 weeks, FDA-approved for CSU age ≥12 refractory to H1 antihistamines

— Onset: some patients respond within 1–2 weeks; full effect by 12–16 weeks

— Continue at least 6 months, then attempt taper or discontinuation

— Adverse effects: injection site reaction, headache, rare anaphylaxis (~0.1–0.2%) — observe 2 hours after first 3 doses, 30 minutes thereafter; prescribe epinephrine auto-injector

— Does not require baseline IgE level for CSU dosing (unlike asthma)

— 3–5 mg/kg/day divided BID, taper to lowest effective dose

— Monitor BP, serum creatinine, magnesium, potassium, lipids, CBC every 2–4 weeks initially

— Limit duration; check for gingival hyperplasia, hirsutism, tremor

— Avoid with grapefruit, statins (rhabdo risk), NSAIDs

— Dupilumab (anti-IL-4Rα) — FDA approved 2025 for CSU inadequately controlled on antihistamines

— Ligelizumab (anti-IgE, investigational)

— Remibrutinib (oral BTK inhibitor, late-stage trials)

— Plasma-derived C1-INH concentrate (Berinert), icatibant (bradykinin B2 antagonist), or ecallantide (kallikrein inhibitor)

— Long-term prophylaxis: SC C1-INH, lanadelumab (monthly), berotralstat (oral)

— Epinephrine, antihistamines, and steroids do not work for HAE

— Narrow-band UVB ×1–3 months as adjunct for refractory CSU and symptomatic dermatographism

Step 3 management: Before initiating omalizumab, document failure of 4× updosed second-generation antihistamine for ≥2–4 weeks, obtain baseline UAS7, screen for active parasitic infection (helminth risk), and counsel on injection reactions plus epi-pen co-prescription.

Omalizumab (anti-IgE monoclonal) — Step 3 of CSU algorithm:

Cyclosporine — Step 4:

Emerging/alternative biologics:

Hereditary angioedema acute attack management (not classic urticaria but high-yield):

Phototherapy:

Special Populations — Elderly and Renal/Hepatic Impairment

— Avoid first-generation H1 antihistamines (diphenhydramine, hydroxyzine, chlorpheniramine) — on Beers Criteria for falls, delirium, urinary retention, glaucoma exacerbation, dry mouth

— Prefer fexofenadine, loratadine, desloratadine, bilastine — minimal CNS penetration and anticholinergic burden

— Cetirizine and levocetirizine: low sedation but some elderly are sensitive — start half-dose

— Doxepin: avoid; orthostatic hypotension, QT prolongation, anticholinergic

— Reconcile polypharmacy: opiates, NSAIDs, ACEi all common urticaria/angioedema culprits and frequently overlooked

— Cetirizine, levocetirizine, desloratadine: reduce dose with CrCl <50 mL/min

— Fexofenadine: reduce dose at CrCl <80 (typical: 60 mg daily)

— Bilastine: no dose adjustment in renal or hepatic impairment — practical choice in CKD

— Loratadine: alternate-day dosing in severe renal/hepatic disease

— Cyclosporine: nephrotoxic — avoid or use cautiously with frequent creatinine, BP, and magnesium checks

— Loratadine and desloratadine undergo CYP3A4/2D6 metabolism — reduce dose in cirrhosis

— Fexofenadine and bilastine minimal hepatic metabolism — preferred

— Avoid doxepin (extensive hepatic metabolism, sedation, encephalopathy risk)

— ACE inhibitors: angioedema can occur years after initiation; switch to ARB (small residual risk)

— NSAIDs and aspirin: common in chronic urticaria — replace with acetaminophen

— Sulfonylureas, allopurinol, antibiotics — review medication reconciliation

Board pearl: In an 80-year-old with chronic urticaria, the right answer is almost never diphenhydramine 50 mg QID — it's fexofenadine or bilastine, dose-adjusted, with explicit deprescribing of anticholinergic culprits and review for ACEi-related angioedema.

Elderly (≥65 years):

Renal impairment:

Hepatic impairment:

Drug-induced urticaria/angioedema in older adults:

Special Populations — Pregnancy, Pediatrics, and Other Subgroups

— Chronic urticaria often flares in pregnancy due to hormonal and immunologic changes

— Preferred antihistamines: loratadine and cetirizine (Category B–equivalent, robust safety data)

— Avoid hydroxyzine in the first trimester (FDA warning for fetal harm at high doses); chlorpheniramine has long safety record but sedating

— Omalizumab: observational pregnancy registry data reassuring; can be continued or initiated when benefit outweighs risk

— Cyclosporine: crosses placenta but used in transplant pregnancies; reserve for severe refractory

— Avoid systemic corticosteroids in first trimester (cleft palate risk historically debated); short bursts in 2nd/3rd trimester acceptable for severe flares

— PUPPP (pruritic urticarial papules and plaques of pregnancy) — third trimester, striae distribution, resolves postpartum; not true urticaria

— Loratadine and cetirizine compatible

— Avoid first-generation sedating antihistamines (infant drowsiness, reduced milk supply)

— Acute urticaria in children: viral infection is the dominant trigger; reassurance and short course of cetirizine or loratadine (weight-based)

— Cetirizine: ≥6 months, 2.5 mg daily up to 10 mg

— Loratadine: ≥2 years

— Fexofenadine: ≥6 months

— Omalizumab FDA-approved for CSU age ≥12

— Chronic urticaria in young children — consider autoinflammatory syndromes (CAPS, NOMID, Muckle-Wells), mastocytosis (solitary mastocytoma, urticaria pigmentosa with Darier sign), serum sickness–like reaction post-cefaclor or amoxicillin

— Exercise-induced anaphylaxis (often food-dependent, especially wheat ω-5 gliadin) — co-trigger pattern, exercise within 4 hours of culprit food

— Latex urticaria in healthcare workers, food handlers (cross-reactive with banana, avocado, kiwi, chestnut)

Key distinction: PUPPP spares the umbilicus and resolves postpartum; pemphigoid gestationis is umbilicus-centered, blistering, autoimmune — antihistamines are insufficient and topical/systemic corticosteroids are required.

Pregnancy:

Lactation:

Pediatrics:

Athletes and occupational exposures:

Complications and Adverse Outcomes

— Most feared acute complication; biphasic reactions in 5–20% occurring 1–72 hours after initial resolution

— Observation period at least 4–6 hours after symptom resolution (longer if severe, refractory, or on β-blockers)

— β-blockers blunt epinephrine response → consider glucagon 1–5 mg IV bolus then 5–15 µg/min infusion

— Tongue, laryngeal, and supraglottic swelling — early intubation by experienced operator; have surgical airway ready

— ACEi angioedema can recur weeks after drug discontinuation

— Chronic urticaria associated with depression, anxiety, sleep deprivation, impaired work productivity — screen with PHQ-9 and address

— Comparable QoL impairment to severe coronary disease

— Chronic systemic steroids → osteoporosis, hyperglycemia, weight gain, cataracts, adrenal suppression, infection

— First-generation antihistamines → sedation, MVAs, falls, cognitive decline, anticholinergic toxicity, urinary retention, cumulative anticholinergic burden linked to dementia risk in observational data

— Cyclosporine → hypertension, nephrotoxicity, hypomagnesemia, gingival hyperplasia, hirsutism, infection, malignancy (skin, lymphoproliferative)

— Doxepin/TCAs → QT prolongation, overdose lethality

— Montelukast → black-box neuropsychiatric AEs including suicidal ideation

— Severe maternal anaphylaxis → fetal hypoxia, preterm labor, demise — IM epinephrine remains first-line in pregnancy

— Missed urticarial vasculitis → undiagnosed lupus, hepatitis C, malignancy progresses

— Missed HAE → fatal laryngeal attacks, unnecessary appendectomies for bowel-wall angioedema mistaken for surgical abdomen

CCS pearl: After any anaphylaxis event, prescribe two epinephrine auto-injectors, demonstrate use, provide a written emergency action plan, refer to allergy, and document Medic-Alert recommendation — missing any of these is a frequent CCS deduction.

Anaphylaxis:

Airway compromise from angioedema:

Quality of life and mental health:

Medication-related adverse outcomes:

Pregnancy and fetal risks:

Misdiagnosis complications:

When to Escalate Care — ICU, Consult, or Inpatient Triage

— Anaphylaxis (airway, breathing, or circulatory involvement)

— Angioedema of tongue, larynx, or symptomatic stridor

— Refractory urticaria with hypotension or syncope

— Hypersensitivity to medication required for ongoing therapy (e.g., chemotherapy) needing desensitization

— Refractory hypotension despite IM epinephrine ×2 doses → epinephrine infusion 0.1 µg/kg/min titrated

— Intubation for airway angioedema

— Biphasic anaphylaxis with hemodynamic instability

— Concurrent severe asthma exacerbation

— Persistent symptoms after ED treatment requiring continued IV antihistamines, steroids, observation

— Severe HAE attack requiring C1-INH infusion and monitoring

— Drug reaction with systemic features (DRESS, serum sickness) initially mistaken for urticaria

— Allergy/Immunology: anaphylaxis evaluation, drug allergy delabeling, food allergen identification, omalizumab initiation, HAE workup, mastocytosis

— Dermatology: urticaria persisting >6 weeks, atypical lesions, suspected urticarial vasculitis (biopsy)

— Rheumatology: suspected SLE, autoinflammatory syndromes

— Hematology/Oncology: acquired C1-INH deficiency, monoclonal gammopathy (Schnitzler)

— Stable cutaneous symptoms, no systemic involvement

— Patient understands trigger avoidance and red flags

— Antihistamine therapy tolerated and partially effective

— Reliable follow-up within 2–4 weeks for response assessment

Step 3 management: A patient discharged from the ED after anaphylaxis needs (1) two epi auto-injectors, (2) written action plan, (3) prednisone 40 mg ×3–5 days and cetirizine ×3–5 days, (4) allergy referral within 1–4 weeks, (5) primary care follow-up within 1 week — count these orders explicitly on CCS.

Emergency department / immediate transfer:

ICU admission criteria:

Hospital admission (non-ICU):

Specialty consultation:

Outpatient management appropriate when:

Key Differentials — Same-Category Causes

— Wheals >24 hours, painful/burning, residual hyperpigmentation or purpura

— Hypocomplementemic (low C3, C4, C1q antibodies) form associated with SLE, Sjögren, hepatitis C

— Diagnosis: skin biopsy showing leukocytoclastic vasculitis

— Treatment: NSAIDs (if tolerated), dapsone, colchicine, hydroxychloroquine, systemic steroids, rituximab

— Urticaria pigmentosa: brown macules with Darier sign (urtication on stroking)

— Adult systemic mastocytosis: persistent tryptase >20, KIT D816V, marrow involvement

— MCAS: episodic flushing, hives, GI symptoms with documented tryptase rise from baseline during episode

— Chronic urticaria + monoclonal IgM gammopathy + fever, bone pain, arthralgia, lymphadenopathy

— Treat with anakinra (IL-1 inhibitor)

— Familial cold autoinflammatory syndrome, Muckle-Wells, NOMID

— NLRP3 mutation; treat with IL-1 blockade

— Third-trimester primigravida, starts in striae, spares umbilicus

— Type I IgE (β-lactams), pseudoallergic (NSAIDs, opiates, vancomycin, contrast)

— Serum sickness–like reaction (cefaclor in children, minocycline)

— Cholinergic: small wheals, exercise/heat

— Adrenergic: small papules with white halo, stress-induced (rare)

Key distinction: Lesions lasting >24 hours with bruising = urticarial vasculitis → biopsy and workup; lesions lasting <24 hours, blanching, no bruising = ordinary urticaria → stepwise antihistamine management. This is the single most tested same-category fork.

Urticarial vasculitis:

Mastocytosis and mast cell activation syndrome:

Schnitzler syndrome:

Cryopyrin-associated periodic syndromes (CAPS):

Pruritic urticarial papules and plaques of pregnancy (PUPPP):

Drug-induced urticarial eruptions:

Cholinergic vs adrenergic urticaria:

Key Differentials — Other-Category Causes

— Chronic relapsing, fixed plaques in flexural areas, lichenification, xerosis — not migratory wheals

— Personal/family history of atopy (asthma, allergic rhinitis)

— Geographic distribution matching exposure (nickel under jewelry, poison ivy linear streaks)

— Vesicles, crusting, scaling rather than transient wheals

— Target lesions on palms, soles, extremities, often post-HSV; lesions fixed, last days

— Elderly patient with pruritic urticarial plaques preceding tense bullae; DIF shows linear IgG/C3 at BMZ

— Migratory tracks (larva migrans); burrows and intense nocturnal itch in web spaces (scabies)

— Unilateral, warm, tender, fixed erythema with fever — not migratory or pruritic

— Painful, edematous plaques + fever + neutrophilia; associated with malignancy, IBD, drugs

— Vasovagal syncope (bradycardia, pallor — distinguish from anaphylactic tachycardia and erythema)

— Scombroid (histamine in spoiled fish) — outbreak pattern, no IgE

— Carcinoid syndrome (flushing, diarrhea, elevated 5-HIAA) — not pruritic, not wheal-forming

— No urticaria, no pruritus, bradykinin-mediated — antihistamines and epinephrine partially effective; consider icatibant in severe airway compromise

Board pearl: Recurrent isolated angioedema without hives is bradykinin-mediated until proven otherwise — workup with C4, C1-INH level and function, C1q and review ACEi exposure; do not commit the patient to lifelong antihistamines for the wrong mechanism.

Atopic dermatitis:

Contact dermatitis (allergic or irritant):

Erythema multiforme:

Bullous pemphigoid (urticarial prephase):

Cutaneous larva migrans, scabies, parasitic infestations:

Cellulitis or erysipelas:

Sweet syndrome (acute febrile neutrophilic dermatosis):

Anaphylaxis from non-allergic causes:

ACEi-induced angioedema:

Secondary Prevention / Discharge Medications / Long-Term Plan

— Epinephrine auto-injector ×2, refills, demonstrate technique, trainer device

— Written anaphylaxis action plan specifying when to use epinephrine and call 911

— Short course oral prednisone 40 mg ×3–5 days

— Cetirizine 10 mg daily ×3–5 days (or longer if hives persist)

— Avoidance counseling for identified trigger

— MedicAlert bracelet recommendation

— Allergy/immunology referral within 1–4 weeks

— Daily second-generation H1 antihistamine, updose to 4× as needed

— Track UAS7 and UCT at each visit

— Reassess at 3–6 months for spontaneous remission (50% remit within 1 year, 80% within 5 years)

— Attempt step-down when UAS7 = 0 for 3+ months; reduce omalizumab interval or antihistamine dose gradually

— Maintain trigger diary; avoid NSAIDs, alcohol, opiates, tight clothing, overheating

— Treat autoimmune thyroid disease with levothyroxine if hypothyroid (does not reliably resolve urticaria)

— Screen and treat anxiety/depression; refer for CBT

— Optimize sleep hygiene; nocturnal antihistamine timing

— Chronic urticaria is not a contraindication to routine vaccines, including COVID-19 mRNA

— History of anaphylaxis to a vaccine component → allergy consult before re-vaccination

— Identify and substitute culprits (ACEi → ARB cautiously; NSAID → acetaminophen)

Step 3 management: In a CCS chronic urticaria case, the longitudinal expectations are 2-week, 3-month, and 6-month follow-ups with UAS7 documentation, escalation per algorithm, and step-down attempts — not indefinite maintenance without reassessment.

Post-anaphylaxis discharge bundle (write each order on CCS):

Chronic urticaria long-term plan:

Comorbidity optimization:

Vaccination considerations:

Medication reconciliation at every visit:

Follow-Up, Monitoring Parameters, and Rehab/Counseling

— Acute urticaria: phone or in-person at 1–2 weeks to confirm resolution; sooner if symptoms worsen

— Post-anaphylaxis: primary care within 1 week, allergy within 1–4 weeks

— Chronic urticaria initiation: 2–4 weeks to assess antihistamine response, repeat UAS7

— On omalizumab: every 4 weeks for injection; assess response at 12–16 weeks; consider stop attempt every 6 months

— On cyclosporine: BP and creatinine q2 weeks for first 3 months, then monthly; CBC, LFTs, lipids, magnesium, potassium periodically

— High-dose antihistamines: sedation, anticholinergic symptoms, QT (uncommon at therapeutic doses but check with hepatic dysfunction and drug interactions)

— Omalizumab: injection reactions, observe per protocol; rare anaphylaxis

— Cyclosporine: BP <140/90 target, creatinine within 30% of baseline, drug levels not routinely needed in dermatologic dosing

— Steroids: glucose, BP, weight, bone density if prolonged

— Trigger diary (food, medication, exercise, stress, sleep, hormonal cycle)

— Wear loose cotton clothing; avoid hot showers, alcohol, NSAIDs

— Cool compresses, oatmeal baths, calamine for symptomatic relief

— Stress reduction, CBT for chronic disease coping

— Demonstrate auto-injector technique annually; check expiration dates

— Allergy & Asthma Network, AAAAI patient handouts

— Urticaria Activity Score app for home tracking

— School action plan for pediatric patients with anaphylaxis history

— Workplace accommodations for cold or solar urticaria (uniform, lighting)

Board pearl: Half of CSU patients remit within 12 months and 80% within 5 years — counsel realistic expectations and plan therapy de-escalation trials, not lifelong maximum-dose therapy.

Follow-up cadence (ambulatory Step 3 framework):

Monitoring parameters by therapy:

Counseling and self-management education:

Patient resources:

Return-to-work / school accommodations:

Ethical, Legal, and Patient Safety Considerations

— Before omalizumab, discuss rare anaphylaxis risk (~0.1–0.2%), requirement for in-office observation after first doses, co-prescription of epinephrine auto-injector, pregnancy considerations, and indefinite duration uncertainty

— Document shared decision-making; cost and prior authorization may shape choice

— Once a patient has had ACEi angioedema, permanent discontinuation must be documented in the problem list and allergy section of the EHR with severity

— Counsel patient verbally and in writing; switching to ARB carries small (~5–10%) cross-reactivity risk and requires informed discussion

— Transition-of-care pitfall: ACEi inadvertently re-prescribed at hospital discharge or by another provider is a sentinel event — reconcile medications carefully

— Cost barriers to epinephrine auto-injectors disproportionately affect uninsured patients

— Discuss generic options, manufacturer assistance programs, and pharmacy substitutions; verify patient can fill the prescription before discharge

— Anaphylaxis action plan must be shared with school nurse with parental consent; stock epinephrine laws vary by state

— Suspected reactions to vaccines or drugs should be reported to VAERS (vaccines) or FDA MedWatch (drugs and biologics)

— Inaccurate "penicillin allergy" labels in the EHR drive use of broader-spectrum, more toxic, and costlier antibiotics — pursue penicillin allergy delabeling in low-risk patients (delayed mild rash, distant childhood reaction) via skin testing or graded challenge

— Document anaphylaxis severity, treatments given, observation duration, prescriptions, education, and follow-up referral; missing any element is a common litigation theme

Step 3 management: At every transition of care (ED → home, hospital → SNF, PCP → specialist), explicitly reconcile ACE inhibitors, NSAIDs, β-lactams, and known urticaria triggers, and update the EHR allergy section with reaction type and date — this single habit prevents the most common preventable harm in this population.

Informed consent for biologics:

ACE inhibitor angioedema — duty to warn and document:

Auto-injector access and equity:

Pediatric assent and school plans:

Mandatory reporting:

Drug allergy labeling:

Documentation and malpractice risk:

High-Yield Associations and Rapid-Fire Clinical Facts

Board pearl: Any stem with "isolated angioedema without hives, on lisinopril for 3 years" → stop the ACEi is the answer, even if angioedema began only recently.

Chronic spontaneous urticaria ↔ autoimmune thyroid disease (Hashimoto, anti-TPO+) in 10–15% — check TSH

Cold urticaria ↔ risk of anaphylaxis from full-body cold-water immersion — counsel against unsupervised swimming

Cholinergic urticaria ↔ rising core body temperature (exercise, hot shower, emotion) — distinguish from exercise-induced anaphylaxis

Delayed pressure urticaria — onset 4–6 h after sustained pressure; antihistamine-resistant; omalizumab helps

Solar urticaria — minutes after UV; broad-spectrum sunscreen, photoprotection, gradual induction of tolerance

Aquagenic urticaria — any water temperature; rare; barrier creams pre-shower

Vibratory angioedema — autosomal dominant, ADGRE2 mutation

NSAID-exacerbated cutaneous disease — 20–30% of CSU patients flare with NSAIDs; use acetaminophen

Schnitzler syndrome — chronic urticaria + monoclonal IgM → anakinra

Hereditary angioedema — low C4 always; C1-INH low (type I) or dysfunctional (type II); acquired form has low C1q

ACE inhibitor angioedema — risk persists for weeks after discontinuation; African American patients at 4–5× higher risk

Vancomycin "red man syndrome" — rate-related histamine release; slow infusion to ≥60 min, premedicate with H1 antihistamine — not a true allergy

Radiocontrast reactions — premedicate with prednisone 50 mg at 13, 7, 1 h pre-procedure + diphenhydramine 50 mg at 1 h

Mastocytosis — Darier sign, baseline tryptase >20, KIT D816V

Omalizumab in CSU — does not require IgE level for dosing (unlike asthma); 300 mg q4 weeks

First-generation antihistamines — on Beers list; avoid in elderly

Montelukast — black-box neuropsychiatric warning

Bilastine — no dose adjustment in renal or hepatic impairment

Omalizumab pregnancy registry — reassuring observational safety data

CSU natural history — 50% remit within 1 year, 80% within 5 years

Board Question Stem Patterns

Key distinction: Step 3 stems test next best step in the algorithm, not pathophysiology trivia — anchor every answer to the EAACI 4-step CSU algorithm or the anaphylaxis ABC + IM epinephrine reflex.

Stem 1 — Acute urticaria in a child: 5-year-old with viral URI develops generalized hives 3 days into amoxicillin. Right answer: stop amoxicillin, observe; reassure most likely viral, not true penicillin allergy; consider delabeling referral later. Wrong answer: lifelong penicillin avoidance label.

Stem 2 — Anaphylaxis after bee sting: Hypotension, wheeze, hives. First step: IM epinephrine 0.3 mg in anterolateral thigh. Wrong answers: IV diphenhydramine first, IV methylprednisolone first.

Stem 3 — Chronic urticaria on standard cetirizine for 4 weeks, still symptomatic, UAS7 = 28: Next step: updose cetirizine to 4× daily (40 mg/day). Wrong answers: add prednisone taper, start omalizumab now, add diphenhydramine.

Stem 4 — Wheals lasting 48 hours, painful, leave bruising: Diagnosis: urticarial vasculitis → skin biopsy, check C3/C4/ANA. Wrong answer: updose antihistamine.

Stem 5 — Isolated lip and tongue swelling, no hives, on lisinopril 2 years: Diagnosis: ACEi-induced angioedema → stop lisinopril permanently, secure airway. Wrong answers: continue ACEi with antihistamines, prescribe epinephrine without stopping the drug.

Stem 6 — Recurrent abdominal pain + facial swelling, low C4: Check C1-INH level and function → HAE. Acute attack: C1-INH concentrate or icatibant, not epinephrine.

Stem 7 — 75-year-old with chronic urticaria, on diphenhydramine 50 mg QID, presents with confusion and urinary retention: Replace with fexofenadine 180 mg daily (Beers).

Stem 8 — Pregnant woman, 2nd trimester, with chronic urticaria: Preferred therapy: loratadine or cetirizine; avoid hydroxyzine in first trimester.

Stem 9 — Patient after omalizumab injection develops hives, hypotension 20 min later: Diagnosis: omalizumab anaphylaxis → IM epinephrine, observation, consider alternative therapy.

Stem 10 — Patient on cyclosporine 3 months for refractory CSU has BP 152/94 and creatinine rise from 0.9 to 1.3: Action: reduce cyclosporine dose, recheck in 2 weeks, treat hypertension; do not simply continue.

One-Line Recap

Urticaria is a clinical diagnosis of transient, pruritic, blanching wheals that resolve within 24 hours, managed acutely with trigger removal and IM epinephrine for anaphylaxis, and chronically with a stepwise algorithm of standard- then 4×-updosed second-generation H1 antihistamines, then omalizumab, then cyclosporine, while always distinguishing it from urticarial vasculitis, mastocytosis, and bradykinin-mediated angioedema.

Board pearl: When in doubt on a Step 3 urticaria stem, ask "is this anaphylaxis?" — if yes, epinephrine first; if no, walk the 4-step algorithm.

Acute urticaria: Most often viral (kids) or drug/food/sting (adults) — supportive care with second-generation antihistamine; anaphylaxis = IM epinephrine first, then IV access, fluids, H1/H2 antihistamines, steroids, 4–6 h observation, two epi auto-injectors at discharge with action plan and allergy referral.

Chronic urticaria stepwise algorithm: Step 1 standard-dose second-gen H1 → Step 2 updose to 4× → Step 3 omalizumab 300 mg SC q4 weeks → Step 4 cyclosporine; document UAS7/UCT; attempt step-down every 6 months; natural remission in 50% by 1 year, 80% by 5 years.

Red flags requiring different management: wheal >24 h or painful/bruising → biopsy for urticarial vasculitis; angioedema without hives → C4, C1-INH workup and stop ACEi; persistent tryptase >20 → mastocytosis workup; chronic urticaria + monoclonal IgM + fevers → Schnitzler.

Step 3 ambulatory non-negotiables: Avoid first-gen antihistamines (Beers), avoid chronic steroids, never substitute antihistamines for epinephrine in anaphylaxis, reconcile ACEi/NSAIDs at every transition of care, and ensure documented anaphylaxis education plus auto-injector access at every discharge.