URTICARIA

Urticaria is a heterogeneous group of disorders
characterized by itchy wheals, which develop due
to evanescent edema of dermis (and sometimes of
subcutis). 5

 

PATHOGENESIS

•  Basic pathology is vasodilatation of vessels
  and leakage of fluid into the surrounding
  tissues.
• Though several mediators are involved, histamine
  released from mast cells plays a key  role.
• Histamine is released from mast cells by several
  mechanisms:
  – Antigen-induced IgE mediated release
  – Classical complement pathway induced.
  -Direct induced by drugs and chemicals.

 

Classification of Urticaria

Urticaria is classified either based on chronicity
or on pathogenesis.

Depending on Duration

Based on its chronicity, urticaria is classified
into:

1. Acute urticaria: Urticaria of <6 weeks duration.
   Etiological trigger is more likely to be identified in acute urticaria.
2. Recurrent acute urticaria: This is recurrent
   episodes of urticaria, each episode lasting <6
   weeks.
3. Chronic urticaria: When urticaria is of >6
   weeks duration. An etiological trigger is less
   likely to be identified in chronic urticaria.

 

Depending on Pathogenesis

Depending on the probable pathogenetic mechanism,
urticaria is classified into several types

Causes of urticaria

 

Clinical features

General features

•   Symptoms: Itching is prominent, especially if wheals are superficial. However, patients tend to rub rather than scratch their lesions, so scratch marks are not seen.
• Morphology: Lesions begin as erythematous macules, which rapidly evolve into pale pink edematous wheals with a surrounding flare . Larger lesions annular with paler centre.
•  Evolution: Wheals last a few hours and resolve
  within 24–48 h leaving behind normal skin.
  Wheals of cholinergic urticaria subside within
  a few minutes.
•   Number and size: Number and size of wheals
  are variable. Cholinergic urticaria (a type of
  physical urticaria) is characterized by pinpoint
  wheals.
• Shape: Shape can be circular, annular, serpiginous
  or bizarre (Fig. 10.7). Dermographic urticaria
  is characterized by linear wheals.
• Angioedema: Half the patients with urticaria
  have associated episodes of angioedema in
  which pale pink swellings occur especially on
  the face affecting eyelids and lips (Fig. 10.8).
  May also be associated with swelling of tongue,
  pharynx, and larynx (when the patient may
  present to the medical emergency). Itching is
  minimal and the swelling may last for several
  days.
• Associated features: Urticaria may be associated
  with systemic symptoms in form of:
  –      Malaise and fever.
   –      Headache.
   –      Abdominal pain, diarrhea, and vomiting.
   –      Arthralgia.
   –      Dizziness and syncope.
   –    Anaphylaxis (with severe acute urticaria).

Other types of urticaria…………..

• Physical urticaria
• Hypersensitivity  urticaria
• Autoimmune  urticaria
• Drug induced urticaria

Physical urticaria

Physical urticaria is a subgroup of urticaria in which a specific physical stimulus produces reproducible whealing . Dermographic urticaria and cholinergic urticaria are commonvarieties of physical urticarias.

Hypersensitivity urticaria

Commonest type of acute urticaria, due to IgEmediated
hypersensitivity to specific antigens.

Causes of hypersensitivity

Autoimmune urticaria

•  Thirty percent of patients with chronic urticaria
  have circulating auto-antibodies present
  in their sera.
• Patients show a positive autologous serum skin
  test (ASST).
• Urticaria more severe, persistent often with systemic manifestations.
• May be less responsive to antihistamines and require immunosuppressive therapy.

 

Drug induced urticaria