Allergic Asthma

Allergic asthma is a form of asthma that is triggered by allergens.

The disease is related to the following processes:  auto-immune and has an incidence of about  27 / 100.000.

Presentation

Asthma symptoms occur due to a combination of inflammation, bronchospasm and mucus production. They include nocturnal coughing, dyspnea, wheezing, pain, pressure and tightness in the chest and vary in type and severity from one individual to another and from episode to episode. Long asymptomatic periods are usually present between episodes, although a subset of patients may show symptoms daily. Disease manifestations in allergic asthma are triggered specifically after exposure to specific allergens, but other forms may be associated with exercise or viral infections of the upper respiratory tract. Episodes are usually mild, although occasionally symptoms may be so severe that they require urgent medical intervention and sometimes hospitalization. Recognition of indicators of severe episodes is critical for prompt and extensive treatment.

Early warning signs precede an asthma episode and are important to identify. In general, they signal a worsening of the disease or the occurrence of a severe episode. They may not be severe themselves and do not stop the patient from performing regular activities. Warning signs include shortness of breath, changes in sleeping habits, persistent nocturnal cough, post-exercise weakness and fatigue, post-exercise wheezing or coughing, changes in mood, overall tiredness and signs of allergies or an upper respiratory infection such as sore throat, sneezing, headache, coughing, congestion and runny nose. The presence of early warning signs should prompt the patient to increase medication intake to try and prevent the occurrence of possible severe episodes.

Without good recognition of early alarming signs, progression into more severe episodes can take place with serious consequences for the patient. Worsening of symptoms can affect daily functioning and habits. Manifestations include a persistent daily and nocturnal cough, rapid breathing, dyspnea, pain and pressure over the chest, muscle spasms in the chest and neck, bluish discoloration of the lips and nails, difficulty talking, anxiety or panic, paleness and sweatiness. The patients are also unable to fully exhale.

Severe episodes generally manifest with a continuous cough, a very high breathing rate, pain or pressure in the chest, inability to talk, anxiety or panic, bluish discoloration of the lips and the fingernails, spasms in the neck and chest muscles, severe wheezing and fatigue.

Workup

Improvement of symptoms in asthma subsequent to the intake of anti-asthmatic medication can suggest the diagnosis but is not sufficient to fully establish it. In general, diagnosis in older patients requires the performance of pulmonary function tests whereas a demonstrated response to empiric treatment is sufficient in children. Pulmonary function tests usually show reversible obstruction but are not frequently performed in children younger than 4 because of the difficulty in establishing cooperation with the child and the absence of standardized measurements.

A ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) that is less than 70% defines respiratory obstruction. Nonetheless, other clinicians have advised the use of different standards [5] [6]. Patients of young age tend to have elevated forced vital capacity, which might decrease the ratio of FEV1/FVC without necessarily signifying an obstruction. On the other hand, reversible obstruction can be demonstrated after the administration of a beta 2 agonist inhaler. In such a case, the FEV1 improves by a mean 12% in asthmatic patients and the forced vital capacity can increase by up to 200 milliliters [7]. An absence of an immediate response requires a two to three-week administration of corticosteroids either orally or intranasally. The appropriate dose is generally 20 milligrams twice-daily for an average patient. Reversible obstruction is not unique to asthma and may also be exhibited in chronic obstructive pulmonary disease. FEV1 levels are also useful in assessing the risk of annual exacerbations. A diagnosis of asthma can be further suggested by peak expiratory air flow, although the latter depends greatly on effort and, thus, is not usually used alone. Peak expiratory air flow is suggestive of asthma when there's a variation of 20% between high and low values.

A number of blood tests can be performed in the workup of asthma. Skin testing is very useful when allergic asthma is suspected. These tests assess for the presence of IgE antibodies that are specific for particular allergens. They are needed when advising patients in avoiding certain environments and when guiding medical therapy. In place of skin testing, blood testing can be performed when there is extensive skin disease, when antihistamine and TCA drugs cannot be stopped, and in the presence of any contraindication for skin tests. Skin testing, however, has higher sensitivity and specificity, and is more affordable. Assessment of eosinophils in the sputum and the serum may also help in guiding therapy, although they are not required for diagnosis. Recent evidence suggests, however, that there is no correlation between response to early and late bronchoconstriction and levels of eosinophils 7 and 24 hours after bronchoprovocation [8]. Although levels of exhaled nitric oxide are functionally significant, no clinical benefit for their use has been demonstrated. They correlate well with inflammation of the airways and are reduced by corticosteroid therapy but clinical studies have shown that their use results in the administration of higher doses of corticosteroids without an associated clinical improvement [9]. Other potential testing modalities that can be employed in the future include exhaled breath condensate and exhale breath temperature. Brain natural peptide can also help in ruling out heart failure as a cause for the symptoms.

Bronchoprovocation tests are useful in excluding the diagnosis of asthma. They are performed after the administration of histamine or methacholine or after exercise and hyperventilation. Methacholine is the most frequently used drug in these tests. A positive test is suggested by a decrease of 20% of FEV1 after the administration of 8 milligrams per ml of methacholine. It is important to note that the drug should be avoided in pregnant women because it can precipitate an asthma attack and because it is classified as a type C Drug, with considerable risks on the fetus.

Imaging tests can be used to exclude other causes. Chest x-rays for example can rule out pneumonia, heart failure and large legions in the airways. They are also performed in cases where symptoms do not respond to therapy, when an adult patient has new onset asthma, or when physical exam reveals unilateral or focal wheezing. On the other hand, a CT scan is recommended when there is suspicion for acute sinusitis since approximately 65% of patients with asthma have sinusitis at the same time. A chest CT scan can also aid in excluding infection, interstitial lung disease, bronchiectasis and bronchiolitis. Finally, a high suspicion in heart failure should prompt the physician to perform an EKG.

Treatment

Treatment is targeted at improving symptoms, enhancing quality of life, decreasing the inflammation that may result in permanent changes to the airways, and minimizing hospitalization and urgent medical treatment. Severe asthma, according to the National Heart, Lung and Blood Institute, is suggested by a peak airflow rate and FEV1 that are less than 40% of predicted values. On the other hand, values that are greater than 70% of what is predicted signal a possibility for discharging the patient from the emergency treatment [10].

Asthma exacerbations require treatment with many agents. These include supplemental oxygen, oral or intravenous corticosteroid therapy, nebulized beta agonist or anticholinergic medication and intravenous fluids. The goal for oxygen therapy is to induce PaO2 and arterial oxygen saturation to surpass 60 mmHg and 90%, respectively. Patients may also require breathing support either invasively or non-invasively. Studies have shown no benefit for antibiotics except when patient suffer from concomitant pneumonia. Other potential treatments are magnesium sulfate and heliox. The latter is a mixture of helium and oxygen [11] [12].

Prognosis

Prognosis of allergic asthma improves considerably when the patient manages to avoid the allergen. It will also depend on the severity of the allergy. Patient with mild allergic reactions are less likely to exhibit severe asthmatic symptoms.

Etiology

The causative factors responsible for asthma can be divided into allergic and non-allergic. Possible allergens are dust mites, food, seasonal pollen, mold spores and animal allergens [1] [2] [3].
Allergens alone cannot account for the development of asthma. Genetic factors are also thought to play a critical role. They may predispose to the disease and influence response to therapy. In fact, genetic variation in the Arg-Arg beta adrenergic receptors is associated with the response to inhaled beta-adrenergic drugs.

Epidemiology

The epidemiology of asthma is extremely complex. Genetic variation is thought to play a very important role and may influence incidence rates within certain racial and ethnic subpopulations. Nonetheless, confounding variables such as culture, overall environment, social and economic status, and geography are difficult to factor in [4].

Sex distribution
Age distribution

Pathophysiology

The pathophysiological mechanisms underlying asthma are diverse. Mucous metaplasia and bronchoconstriction are characteristic of the disease, and are mediated by the release of inflammatory cytokines such as IL 25 and IL 33. These, in turn, activate specialized cells like mast cells, basophils and type 2 lymphocytes. Genetic variations in alleles that code for cytokines like IL33 have been also identified and are thought to be associated with the disease.

Prevention

Environmental control can play a very significant role in preventing the development of asthma, as evidenced by randomized control studies. Preventive measures include remediation of allergens, especially those of cats, cockroaches, mouse, dog and mold. On the other hand, vitamin supplementation, especially vitamin A and D, can improve the immune system and potentially decrease the risk for asthma development. Drugs that have also shown promise include Palivizumab, a monoclonal antibody that is normally used against respiratory syncytial virus. The drug has been shown to reduce morbidity in preterm infants for up to 78%. Other Studies have reported that prophylaxis with Palivizumab may decrease recurrent wheezes from 10 to 50% in the first year of life. Nonetheless, more studies need to be performed to directly access the role of Palivizumab in the prevention of asthma.

Summary

Allergic asthma is a medical condition in which allergens trigger an asthmatic reaction. Both genetic and environmental factors are thought to underlie the disorder. Early intervention in regards to a multitude of allergens such as dust mites, pollen, cockroaches, dogs and cats can help in limiting or preventing the development of the disease. Patients usually present with symptoms typical of asthma after exposure to particular substances. These include wheezing, nocturnal cough, chest tightness or pain and difficulty breathing. Symptoms can vary from mild to severe, requiring urgent medical intervention. Diagnosis is established with pulmonary function tests and allergic skin testing. Treatment is based on allergen avoidance as well as symptomatic treatment.

Patient Information

Allergic asthma is a medical condition that describes asthmatic symptoms after exposure to allergens. The causative factors responsible for the condition are diverse and involve both a genetic predisposition and environmental triggers. Patients present with a range of symptoms that include nocturnal cough, dyspnea, chest pain and pressure, wheezing, and difficulty talking. Episodes can be mild but also severe and might require urgent medical care. Diagnosis is established with testing that assesses respiratory functioning and sensitivity to specific allergens. Treatment includes inhaled medication that relieve obstruction in the respiratory tract, as well as oral or intravenous corticosteroids and oxygen supplementation in medical emergency. Prognosis improves if the patient is able to avoid the allergen but also depends on the severity of the allergic reaction.

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References

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