Description

• Urticarial lesions are best described as raised, pruritic, circumscribed erythematous papules.
  • Single lesions may coalesce as they enlarge, forming generalized, raised, erythematous areas.
  • Transient, typically lasting several hours
  • Also known as “hives” or “nettle rash”
  • Acute: <6 weeks’ duration
  • Chronic: >6 weeks’ duration
• Other similar but non-urticarial entities:
  • Angioedema
    • Urticarial-like lesions
    • Form in the deep dermal, subcutaneous, and submucosal layers
  • Anaphylaxis
    • Hypersensitivity reaction after exposure to an antigen
    • Producing respiratory compromise secondary to airway edema, urticarial rash, pruritus, and hypotension; can lead to shock

Epidemiology

• Female-to-male ratio of 3:2
• No variation in race

General Prevention

When a trigger is identified, avoidance is the main preventive measure.

Pathophysiology

• Immune mediated
  • Antigen is cross-linked to IgE on a mast cell.
  • This event causes mast cell activation, leading to the release of vasoactive mediators, such as histamine, leukotrienes, prostaglandin D2, platelet-activating factor, and other vasoactive mediators.
  • These vasoactive mediators cause pruritus, vasodilatation, and capillary leak, which lead to the characteristic findings.
  • Common triggers include some medications such as penicillins, foods such as milk or eggs, and envenomations.
• Non–immune mediated
  • Degranulation of mast cells secondary to other non-IgE reactions such as physical changes, chemicals, some medications such as β-lactams and sulfa-containing drugs, and some foods
• Autoimmune mediated
  • Degranulation of mast cells caused by cross-linking of IgE by IgG or IgG binding to the high-affinity IgE (FcεRI) receptor on mast cells

Etiology

• Acute urticaria
  • Viral infections are thought to make up approximately 80% of all cases of acute urticaria in children. Most commonly isolated causes include the following viruses:
    • Picornavirus
    • Coronavirus
    • Epstein-Barr
    • Hepatitis A, B, and C
  • Parasitic infections
  • Bacterial infections (especially group A strep)
  • Medications: most frequently reported include the following:
    • NSAIDs
    • Opiates
    • β-lactams
    • Vancomycin
  • Radiocontrast
  • Foods
  • Transfusion of blood products
  • Food additives and dyes
  • Natural remedies including cranberry, feverfew, glucosamine, and ginger
  • Insect venom including bees, wasps, hornets
• Chronic urticaria
  • Idiopathic: Most have an unknown cause, but many feel that an association with an autoimmune mechanism is likely.
  • Physical (~20–30%)
    • Dermatographism (9%): Stroking of skin using mild-to-moderate pressure with fingernail or hard object causes linear urticaria at site of contact.
    • Cholinergic (5%): diffuse erythema and elevated but pale urticarial lesions; intense pruritus; associated with sweating reflex, so often associated with overheating or exertion; may be worsened in combination with other triggers in specific combinations
    • Cold (3%): urticarial lesions present at areas of skin exposed to low temperatures; familial and nonhereditary forms
    • Aquagenic: Urticarial lesions arise when the patient is exposed to water (e.g., bathtub, swimming pool).
    • Delayed pressure/vibratory: Deep or prolonged pressure on skin produces significant urticaria and often angioedema. Vibratory urticaria is a form of delayed pressure urticaria caused by repetitive vibration (e.g., use of a jackhammer).
  • Mast cell disease
    • Urticaria pigmentosa: excessive number of mast cells in skin, bone marrow, lymph nodes, and other tissues; flares characterized by pruritus, flushing, tachycardia, nausea, and vomiting
    • Systemic mastocytosis
  • Systemic disease
    • Rheumatologic
      • Urticarial vasculitis: erythematous wheals that resemble urticaria but histologically appear as leukocytoclastic vasculitis; often presents with systemic symptoms and lasts >24 hours
      • Cryopyrin-associated periodic syndromes can present with urticaria, such as Muckle-Wells syndrome: chronic recurrent urticaria, deafness, amyloidosis, and arthritis.
    • Neoplasms
    • Infections: parasites especially noted to cause chronic urticaria
    • Autoimmune: antibodies to IgE or IgE receptor (FcεRI)
    • Hashimoto disease, hypothyroidism