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Urticaria may be acute (<6 weeks duration) or chronic (>6 weeks duration). Angioedema is frequently associated with urticaria but the two may occur independently.
A. Incidence
Index
Acute urticaria is said to affect 10%-20% of the population at some time during life. It is not uncommon in childhood, but the greatest incidence appears to be in young adults (15%). Chronic urticaria occurs more frequently in mid-life, especially in women.
B. Aetiology
Index
A clinical classification is given in Table 1. In chronic urticaria a causative agent or precipitating cause may be established in only about 10% to 30% of cases. Therefore, most chronic urticaria is idiopathic. In acute urticaria the chances of determining the cause are higher. For example as many cases of acute urticaria in children may be associated with a viral, bacterial or parasitic infection (not always clinically apparent). Acute urticaria and angiooedema may also be caused by allergen exposure including insect stings or food or drug ingestion. Some of the more common drugs include penicillin, cephalosporins and sulphonamides. Opiates may act directly on mast cells to cause histamine release. Aspirin and other non-steroidal anti-inflammatory agents can cause urticaria or angioedema in the same way. Angiotensin converting enzyme inhibitors are a common cause of drug induced angioedema.
Table 1
Classification of Urticaria and Angioedema
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a.) IgE mediated
Foods (shellfish, nuts, milk, eggs, legumes, fruits) Chemicals and therapeutic agents (penicillin, cepahalosporins) Foreign proteins (venoms, insulin, latex) b.) Immune complex- and complement-mediated
Blood and blood products, cuprophane hemodialysis membranes
Opiates, radiographic contrast media, vancomycin, petamidine, Dextran, aspirin (and other NSAID)
a.) Physical stimuli
Cold urticaria, cholinergic urticaria, dermatographism, solar urticaria (angio-oedema), exercise-induced urticaria or angio-oedema
b.) Underlying medical disease Urticaria pigmentosa (systemic mastocytosis), cutaneous vasculitis, serum sickness, malignancy, infections (viral, Parasitic), acquired C1 inhibitor deficiency
c.) Hereditary Hereditary angioneurotic-oedema, hereditory vibratory angio-oedema, familial cold urticaria, C3b complement deficiency
d.) Papular urticaria
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C. Clinical Features
Index
Urticaria consists of raised, erythematous skin lesions that are itchy, tend to be evanescent in any one location, and generally are worsened by scratching. (Plates 12,13 on pages 134, 135). Angio-oedema is a reaction similar to urticaria except that it occurs in deeper tissue and is characterised by asymmetrical swelling of tissue. Pruritus, however, is uncommon with angio-oedema which more typically has a burning sensation. Any area of the body may be involved, although the perioral and periorbital regions, tongue, genitalia and extremities are involved most frequently. Laryngeal oedema is the most serious manifestation of angio-oedema.
D. Diagnosis Tests
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1. Clinical Evaluation
A careful history and physical examination are the most important aspects of the evaluation of urticaria. History must include: features of the rash, suspected precipitating causes (drugs, foods etc.), frequency of crops of the rash, and duration. The characteristics and distribution of the rash must be ascertained on examination.
2. Laboratory Tests
Laboratory tests are of limited value in the investigation of urticaria. Skin prick testing or RAST are generally not helpful. In addition, both false-positive and false-negative skin tests are common. Skin tests should be considered only in special circumstances e.g. patients who relate urticaria to food ingestion. If skin tests are negative then foods are probably not the cause. If all skin tests are positive, dermatographism is probably present. Patients with chronic urticaria with no obvious identifiable cause should be referred to a specialist for further evaluation.
E. Treatment
Index
1. Avoidance of precipitating Cause
If an avoidable allergen or any precipitating cause has been identified, avoidance is the most effective treatment.
2. Drug Therapy
Antihistamines are the first line medication for acute or chronic urticaria. Classical antihistamines such as hydroxyzine (Aterax), promethazine (Phenergan), mepyramine are usually effective for most cases of urticaria if given in adequate doses. Their main side effect is sedation, which limits their use. Hydroxyzine has a relatively less sedative effect and apart from its antihistaminic effects, has anticholinergic and antiserotonin effects as well.
The new generation antihistamines such as astemizole, terfenadine, cetitrizine and loratidine offer some valuable new options (non-sedating or minimal sedation and longer-acting), especially for chronic urticaria. Astemizole and terfenadine may rarely cause torsade de pontes arrhythmia at toxic doses. Ketotifen has also proven effective for urticarial syndromes. In refractory patients, oral corticosteroids are frequently required and occasionally an oral sympathomimetic agent such as ephedrine may be added. Subcutaneous adrenaline may be administered to the patients with acute-onset confluent urticaria or angio-oedema and must be given if there is any suspicion of oropharyngeal or multi-organ involvement (anaphylaxis).
Forms of urticaria and angioedema:
(requiring special mention)
Index
1. Cholinergic Urticaria
Index
This is a common form of chronic urticaria (5% to 7%). It appears as small wheals 1-2 mm in diameter surround by large areas of erythema (flares) and frequently involves the skin of the neck and chest. It is associated with increased body temperature e.g. after exercise, hot showers, emotional stimuli etc. There is no reliable diagnostic test. Hydroxyzine (Aterax) is the treatment of choice, but if it is ineffective, other antihistamines or combinations may be tried. (Plate 16 on page 136).
2. Cold Urticaria
Index
Cold urticaria is characterised by the rapid onset of urticaria or angio-oedema after cold exposure (e.g. cold weather, local application of cold, swimming in cold water). Lesions are usually localised to exposed areas but sudden total body exposure, as in swimming, may cause hypotension and result in fatalities. Although this condition is idiopathic in most cases, in adults cold urticaria has been associated with cryoglobulinaemia, cold agglutinin disease, and paroxysmal cold haemoglobinuria. The diagnosis of cold urticaria can often be confirmed by placing an ice cube on the forearm for 4 minutes, and observing over the next 10 minutes for the appearance of an urticarial lesion during rewarming at the test site (Plate 15 on page 136). Treatment should consist of limited cold exposure, proper clothing and oral cyproheptadine (Periactin), although other antihistamines such as doxepin may be useful. In cases where an abnormal protein is present, treatment of the underlying disease is necessary.
3. Hereditary Angioedema (HAO)
Index
HAO is caused by a deficiency of the C1 inhibitor of the complement system. Rarely, patients may develop an acquired C1 inhibitor deficiency in association with certain underlying disease e.g. SLE or a malignancy. Other hereditary syndromes include familial cold urticaria syndrome, hereditary vibratory angioedema, C3b inactivator deficiency and a familial urticaria, amyloidosis and nerve deafness syndrome. The treatment of HAO is dependent on the presenting complaints. The usual forms of treatment for angioedema are generally ineffective. Tracheostomy may be necessary in emergency situations where laryngeal oedema has occurred. Supportive therapy such as intravenous fluids, fresh frozen plasma and analgesics may be required for other manifestations of the disease. Attenuated androgens such as danazol and stanozol are effective and relatively safe and can be used for long term control.
4. Papular Urticaria
Index
Papular urticaria is a term used to describe crops of grouped, itchy, erythematous papules or small blisters. The pathogenesis is unknown but it is known to be caused by insect bites. The usual offending insects are fleas or mites on domestic cat and dogs, but the human flea, bedbug mosquito and dog louse are sometimes incriminated. Worldwide fleas and bedbugs are the most common causes. Papular urticaria is rare in the first year of life. It afflicts predominantly children between the ages of 2 and 7 years, but may occur in adults. The incidence decreases with age, presumably due to specific hyposensitization by repeated bites. The condition is frequently seasonal, especially in temperate climates where they are worst in the summer. It may also be perennial. The eruption consists of wheals or firm papules, or of wheals surmounted by papules. There may be bullae, especially on the legs. Lesions are often grouped in clusters, developing in crops at irregular intervals. Each lesion persists for 2 to 10 days and may leave behind pigmentation. The lesions tend to occur mainly on the thighs, buttocks and lower trunk (“bathing-costume area”) but the distribution depends largely on the insect responsible; in some cases the forearms, arms and face are involved. Fleas may cause papular urticaria where two to three lesions are seen in a row. (Plate 14 on page 135). The lesions are often excoriated and recurrent impetigo may be a troublesome complication. The majority of children “outgrow” papular urticaria within 3 to 4 years of its onset. Occasionally, the condition persists into adolescence or adulthood.
The treatment of papular urticaria is supportive. Therapy includes relieving pruritus, prevention or of secondary infection.
For the relief of pruritis, topical application of calamine lotion may suffice. Oral antihistamines e.g. hydroxyzine (Aterax) may also be given in full doses. Topical antihistamines are inadvisable as they are relatively inactive and the risk of allergic sensitization is high. Topical steroids are often helpful in refractory cases or if secondary eczematization has occurred. Crotamiton 10% (Eurax) is also effective in certain cases.
Good skin care is essential for prevention of secondary infection. For isolated or minor infected lesions, topical application of an antiseptic e.g. betadine usually suffices. Systemic antibiotics must be given for severe or extensive infection of if clinically evident secondary infection and adenitis are present. Erythromycin should be the first choice oral antibiotic.
Examination of bedding and the children’s play areas for insects may provide a clue to the cause. Offending insects in the house must be eliminated by fumigation. Insect repellants may also be helpful. Pets should be washed and if offending insects cannot be eradicated by commercially available pesticides, the public health authority should be consulted.