Asthma is a chronic inflammatory and obstructive disease of the airways. Asthma has defied a clear definition that distinguishes it from similar and overlapping conditions. It is characterized by airway hyper-responsiveness and recurrent episodes and is relieved by bronchodilating medications. More common in males in those <18 years while in those above 18 years, it’s more common in females
Allergic Asthma- is the most common type. It begins in childhood and is associated with atopy.
Non-allergic Asthma– is a type that is not associated with atopy and generally responds poorly to medication. The onset is typically above 40 years of age.
Aetiology
The exact cause of Asthma is unknown
Risk factors;
- Genetic factors
- Atopies- such as atopic dermatitis and a history of allergies
- Low socioeconomic status
Triggers include;
1. Allergic Asthma- environmental allergens such as pollen, mould spores, dust, domestic animals, flour, dust
2. Non-allergic Asthma- Upper respiratory tract infections, Cold weather, exercise, aspirin, beta-blockers, tobacco smoking, stress
Pathophysiology
1. Allergic Asthma-
- These individuals have a prior phase of sensitization
- inhalation of the allergen causes degranulation of mast cells and release of histamine
- This type is associated with elevated serum IgE
2. Non-allergic Asthma-
- The irritant causes a neutrophilia that is associated with submucosal oedema and, ultimately, airway obstruction
- In aspirin-induced Asthma, the metabolism of arachidonic acid is shunted through the lipooxygenase pathway to the production of asthmogenic leukotrienes
- In exercise-induced Asthma, hyperventilation causes water loss from the pericellular lining fluid of the respiratory mucosa, triggering mediator release
Both types are linked to 3 processes;
A) Airway hyper responsiveness- integral to the diagnosis of Asthma
B) Airway inflammation- symptoms are caused by inflammation. T helper 2 cells play a crucial role
C) Airway obstruction- this is due to submucosal oedema, increased airway secretions, bronchospasm, and ultimately, hypertrophy of airway smooth muscle
Clinical presentation
- Typical symptoms are recurrent wheezing, breathlessness, chest tightness and cough.
- Some patients will not report all four symptoms.
- Patients with intermittent Asthma are usually asymptomatic between exacerbations.
- Asthma usually displays a diurnal pattern with symptoms worsening at night and early morning.
- Cough variant asthma – where cough is the dominant symptom
- Ask about a history of upper respiratory infection symptoms
- Enquire about exposure to allergens
- Also, enquire about drugs such as beta-blockers, aspirin, alcohol and food containing salicylates, the oral contraceptive pill, cholinergic medication and prostaglandin F2 alpha
- A severe form of Asthma is particularly common in women. Aspirin-induced Asthma is also common in middle-aged women
Physical examination ;
- Musical, high-pitched wheezes, although not a specific finding
- Signs of severe airway obstruction- tachypnea, tachycardia, “silent chest”, tripod position, use of accessory muscles for breathing and a pulsus paradoxus
- Examine for other signs of atopy such as eczema and the presence of nasal polyps
- Rarely, a vasculitic rash may be present, suggesting eosinophilic granulomatosis
*Clubbing is not a feature of Asthma
Diagnosis
It’s predominantly clinical and is based on the history, lung function and other tests.
1. Spirometry is preferred for the lung function, and it is used to measure the FVC and the FEV1
2. A peak flow meter may be used if spirometry is unavailable. Patients are asked to record the peak flow readings in the morning and evening.
3. A trial of glucocorticoids may aid in establishing the diagnosis by demonstrating an improvement in the peak expiratory flow( PEF) or FEV1
4. Demonstration of airway hyper reactivity( AHR) can be demonstrated using challenge tests, especially in those with normal lung function but have symptoms suggestive of Asthma. AHR has a high negative predictive value
5. Exercise tests- when symptoms are predominantly due to exercise
6. Skin prick tests,
7. Total allergen-specific IgE
8. Peripheral blood eosinophilia
9. Chest X-ray- often normal. Lobar collapse if mucus obstructs a large bronchus, flitting infiltrates if complicated by aspergillosis
10. High-resolution CT- may show bronchiectasis
11. Exhaled nitric oxide
A diagnosis of Asthma is made by;
Compatible history plus either/or;
- FEV1 ≥12% ( and 200ml )increase following bronchodilator administration/ glucocorticoids trial. Greater confidence if thee increase is ≥15% and >400ml
- FEV1 ≥15% decrease after 6 minutes of exercise
- >20% diurnal variation in the PEF on ≥3 days in a week for two weeks
Categories of asthma severity;
1. Intermittent Asthma
- Two or fewer nocturnal awakenings per month
- Use of SABAs to relieve symptoms two or fewer days in a week
- If daytime symptoms occur two or fewer days in a week
- No interference with normal activities between exacerbations
- FEV1 measurements between exacerbations are within the normal range
- FEV1/FVC ratio between exacerbations is normal
- One or no exacerbations requiring glucocorticoids per year
2. Mild persistent
- 3 to 4 nocturnal awakenings per month due to asthma( but fewer than every week)
- Symptoms more than twice weekly
- Use of SABAs for relief more than two days of the week, but not daily
- Minor interference with normal activities
- FEV1 is within the normal range
3. Moderate persistent
- Nocturnal awakenings as often as once per week
- The daily need for SABAs for relief
- FEV1≥60% and <80% of predicted and FEV1/FVC ratio below normal
- Some limitations in normal activity
4. Severe persistent
- Daily nocturnal awakenings
- Reliever medication required several times a day
- Presence of symptoms throughout the day
- Extreme activity limitation
Management
1. Patient education and setting goals;
Patients should be engaged in their management whenever possible. This entails;
- A full explanation of the condition
- The triggers and how they can be mitigated
- The medications used, and the correct inhaler use technique
- PEF monitoring and its use to guide management
- Adherence to medication
- Asthma exacerbations
- A personalized Asthma action plan is a document that provides instructions to the patient on what to do at home
2. Controlling triggers- the allergens should be identified for every patient. Some measures include;
- Reducing exposure to or removing pets
- Replacing carpets with floorboards to reduce house dust mite exposure
- Smoking cessation
3. Pharmacologic therapy
There is a stepwise approach to the management of Asthma
1. Step 1
- Inhaled Short-acting beta-agonists(SABA) as needed, e.g. salbutamol
- For mild Intermittent Asthma
- However, a history of an exacerbation should prompt a step up
2. Step 2
- Inhaled Low dose glucocorticoid(e.g. budesonide, beclometasone) plus SABA on an as-required basis
- For mild persistent Asthma
- Higher doses may be required in smokers
- Alternatives are theophylline, leukotriene receptor antagonists and chromones
3. Step 3
- Inhaled low dose glucocorticoid plus a LABA(e.g. formoterol). Fixed combinations are available.
- This prevents the use of LABA as monotherapy which is associated with life-threatening attacks and asthma death. It also increases adherence and is convenient
- For moderate persistent Asthma
- Oral leukotriene receptor antagonists are less effective as add-on therapy
4. Step 4
- Inhaled medium or High dose glucocorticoid plus a LABA
- For severe persistent Asthma
- Leukotriene receptor antagonists, theophylline, antimuscarinics and slow-release beta-agonists may be considered
5. Step 5
- Oral Prednisone. Those receiving three or more courses per year will require bisphosphonates due to the risk of osteoporosis.
- Omalizumab, if symptoms persist, particularly for allergic Asthma
- Mepolizumab in those with eosinophil-mediated disease
*Once Asthma is controlled, inhaled or oral glucocorticoids should be stepped down to the lowest dose at which effective control of Asthma is maintained
