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
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 of 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
in Indigenous peoples from northern Australia or those in the tropics, you MUST exclude strongyloidiasis BEFORE giving systemic steroids
systemic steroids has a 60% mortality in these patients ⇒ exclude this condition first!
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.
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
lesions last > 24hrs hence need to exclude vasculitic causes
FH recurrent or chronic urticaria
aetiology
acute "ordinary" urticaria
a self-limiting urticaria usually due viral infections, or, less commonly, to contact with, or ingestion of an allergen (food or medications), or following an insect sting
weals are well defined raised lesions with a smooth surface, may be red or white, surrounded by a red or white flare
weals range in size from a few millimetres to many centimetres in diameter
they are assymetric and randomly distributed on the body and may affect any site
individual weals last no more than 24 hours and do not leave any marks behind.
most will settle within 10-14 days and are best managed with avoidance of trigger and hot baths and symptomatic relief with antihistamines
it may be part of more serious allergic reactions such as anaphylaxis in which case early Rx with im adrenaline, corticosteroids and antihistamines, and hospital observation is indicated
chronic inducible "physical" urticaria
these are acute, recurrent, localised to trigger region, SHORT DURATION (last <1hr except for delayed pressure urticaria which lasts for hours to days) wheal-type reactions that occur in response to local physical stimuli such as:
5% of people develop raised linear,wheal-like dermographism within 30min following firm stroking of the skin
acetylcholine released during sweating in cholinergic urticaria
smaller wheal lesion “spots” especially on upper trunk and arms which tend to resolve after 60-90 minutes
rarely affects the palms, soles or the armpits
those who are more severely affected may experience systemic symptoms such as headaches, salivation, palpitations, fainting, shortness of breath, wheezing, abdominal cramps and diarrhoea, and rarely may develop anaphylaxis
cold air or water in cold urticaria
common form causes rapid onset urticaria to face, neck and hands on exposure to cold
rare hereditary form causes generalised urticaria 9-18 hours after cold exposure
local heat in heat urticaria
a contact factor in contact urticaria
water of any type or temperature in aquagenic urticaria
sun exposure in solar urticaria
urticaria follows UV exposure within minutes and generally resolves over a few hours, rarely lasting more than 24 hrs.
firm pressure in delayed pressure urticaria
such as from tight clothing causes gradual onset wheal-like lesions after 6hrs following trigger and lasts 8hrs-3 days
other subacute forms of urticaria
strongyloidiasis may cause urticarial lesions around the waist and buttocks
an acute eruption of target-shaped lesions on the hands, feet, knees and elbows.
unlike urticarial weals, individual lesions persist for ten days to 3 weeks and there may be mucosal lesions
may be recurrent, usually due to herpes simplex virus infection
urticarial multiforme
a morphological subtype of urticaria, a benign cutaneous hypersensitivity reaction predominantly mediated by histamine seen in paediatric patients that is characterized by the acute and transient onset of blanchable, annular, polycyclic, erythematous wheals with dusky, ecchymotic centers in association with acral oedema (hands, feet, face)
rash starts within 14 days of a new medication (except in drug hypersensitivity syndrome, when they arise within eight weeks of starting a new medication)
symmetrical and tends to be most severe on the trunk
peeling may occur as it resolves and dark marks may persist for days to weeks
urticaria pigmentosa
mainly seen in infants, and is a form of cutaneous mastocytosis in which there are brown macules and papules.
autoimmune blistering diseases
these may initially present with symmetric urticarial lesions esp of trunk and skin flexures, several days or weeks before blisters appear
eg. bullous pemphigoid (mainly elderly), pemphigoid gestationis, linear IgA bullous dermatosis, epidermolysis bullosa acquisita
pruritic urticarial papules and plaques of pregnancy (PUPPP)
an eruption occurring during the last few weeks of pregnancy, usually in a first pregnancy
usually start in the stretch marks (striae gravidarum)