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urticaria

urticaria

introduction

  • urticaria or hives is a common pruritic wheal-type generalised rash which has many causes, the most common being viral infections (50%), food allergic reactions (25%), drug reactions (10%), idiopathic (20%), inhalants (2%), bites (1%), contact (0.2%)
  • ~9% of people develop an acute urticaria
  • ~2% of people develop a chronic urticaria (lasts >6 weeks) - mainly young children and the elderly
  • 60% of cases are also associated with angioedema which typically is painful rather than itchy as it is deeper layers of skin or mucosa, and lasts 3 days. Angioedema associated with urticaria is less worrisome than that occurring without urticaria.
  • the lesions can be confused with erythema_multiforme although these lesions are not pruritic
  • IgE hive wheals individually only last up to 24hrs, lesions lasting longer than this suggest a vasculitic aetiology or delayed pressure urticaria rather than usual urticarial mast cell release aetiology
  • an attack if urticaria usually lasts a week or two, but may last longer
  • urticaria caused by food presents within 2hrs of ingestion with 90% presenting within minutes, thus ingestions more than 2 hr prior to onset are extremely unlikely to be due to that food.
  • ~94% of cases of food allergy result in a skin reaction such as urticaria
  • delayed onset serum sickness reactions such as those following Rx with cefaclor also cause urticarial like lesions, but in association with joint effusions

Mx of acute urticaria

  • corticosteroids do not provide much benefit to acute urticaria and thus their risks generally outweigh benefits

  • remove trigger but avoid advising diet restrictions unless strongly suspect a specific NEW food - avoidance of foods increases risk of allergy if allergy does not already exist to that food in those with allergies.
  • daily non-sedating antihistamines (H1) for at least 3 days and up to 3 wks
  • consider adding promethazine dose at night
  • if poor response try changing non-sedating antihistamine and if still troublesome, consider adding ltra and referral to immunologist

chronic urticaria

Mx of chronic urticaria

  • non-sedating antihistamines (H1) for 2weeks, consider increasing dose
  • consider adding ltra
  • consider adding corticosteroids for 3-7 days
  • investigations are usually fruitless (1 in 2000 will detect treatable condition such as thyroiditis) but many do them anyway, such as FBE, ESR, CRP, LFTs, TFT but DON'T bother with total IgE levels are this is useless
  • consider referral to immunologist
  • consider skin biopsy if ? Vasculitis
  • stool for helminths
  • consider hep B, C serology
  • consider ANA, Rh factor, cryoglobulins
  • consider using cyclosporin A, dapsone, omalizumab

indications for referral to immunologist

  • strongly suspected specific trigger
  • severe attacks
  • lasting >6wks
  • lesions last > 24hrs hence need to exclude vasculitic causes
  • FH recurrent or chronic urticaria

aetiology

acute urticaria

physical urticaria

  • 5% of people develop raised wheal-like dermographism within 30min following firm stroking of the skin

pressure urticaria

  • rarely, firm pressure such as from tight clothing causes gradual onset wheal-like lesions after 6hrs following trigger and lasts 8hrs-3 days.

cholinergic or stress urticaria

  • high levels of physical or emotional stress or over-heated skin may result in urticaria, although lesions are typically smaller than usual urticarial wheals
  • spots tend to resolve after 60-90 minutes

cold urticaria

  • common form causes rapid onsert urticaria to face, neck and hands on exposure to cold
  • rare hereditary form causes generalised urticaria 9-18 hours after cold exposure

solar urticaria

  • urticaria follows UV exposure within minutes and generally resolves over a few hours, rarely lasting more than 24 hrs.

other subacute forms of urticaria

shiitake flagellate dermatitis

  • an intensely pruritic 1mm micropapular erythematous rash which looks like whip marks due to Koebnerization due to patient scratching
  • rare outside of Asia
  • occurs 12hrs to 5 days after eating shiitake mushrooms (when eaten raw or only lightly cooked) in ~2% of people and most resolve within 3 weeks
  • appears to be a reaction to lentinan, a thermolabile polysaccharide
  • similar rash can occur with:
    • use of bleomycin, peplomycin or docetaxel
    • Adult-onset Still disease

chronic urticaria

  • urticaria lasting > 6 weeks, often lasting 1-20years
  • rarely due to allergy
urticaria.txt · Last modified: 2019/05/22 10:03 by gary1