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Metacholine: the test for asthma diagnosis

The methacholine challenge test, or nonspecific bronchial provocation, is a diagnostic analysis aimed at diagnosing and confirming the presence of bronchial hyperresponsiveness, which is a state of increased sensitivity of the bronchi to stimuli that would be harmless in normal subjects. This examination lasts about an hour and is particularly useful for confirming the suspicion of bronchial asthma even when the patient does not present symptoms at the time of the visit.

The patient undergoes inhalation of a bronchoconstrictor drug, causing the bronchial pathways to react with the stimulus of coughing and obstruction for self-defense. This mechanism is defined as bronchial hyperresponsiveness because it causes bronchospasm, which is an acute obstruction of the airways, the main symptom of asthmatic disease.

Methacholine challenge test: What is it for?

There are various methods for performing bronchial provocation; in particular, methacholine is a pharmacological substance capable of activating bronchial smooth muscle in the parasympathetic nervous system, causing bronchospasm in sensitive individuals.

The main purpose of a methacholine challenge test is to confirm the diagnosis of asthma even when the patient is observed at a distance from when they have symptoms. Often, a spirometric examination and bronchodilation may appear normal even though a person is affected by asthma. For this reason, in the case of suspected asthma, it is advisable to undergo a careful methacholine challenge test, which proves to be highly reliable in terms of the final diagnosis.

It should be noted that spirometry and possibly the methacholine challenge test are essential to establish the diagnosis of asthma with certainty. Many patients are diagnosed as asthmatic, even with consistently normal spirometry, while they are affected by other conditions that require different treatments; the methacholine challenge test is very useful for obtaining a definitive diagnosis of asthma.

Methacholine challenge test: Procedure and preparation guidelines

The methacholine test is performed with an initial spirometry to record the baseline respiratory status. The patient is then administered increasing doses of methacholine via aerosol (up to a maximum standard dose), and a control spirometry is performed after each inhaled dose.

If there is a 20% reduction in FEV1 (bronchial obstruction index) compared to the initial value, the test is considered positive and is therefore terminated. At this point, a bronchodilator drug is administered, and a control spirometry is performed to verify the restoration of lung volumes.

The duration of the test can vary between 15 minutes and 1 hour. At the time of the examination, the patient must be in good health and provide some useful information to the specialist, such as: the possible presence of asthma symptoms or respiratory infections, any vaccinations in the last two months, pregnancy status, the presence of cardiac problems or signs of hives in the last few weeks.

Before the methacholine test, the patient must avoid consuming coffee, tea, Coca-Cola, chocolate, and smoking (at least 2 hours before the test). Any ongoing asthma treatments with bronchodilator drugs must be discontinued, upon the doctor’s recommendation, at least 12 hours before the start of the test.

Spirometry with methacholine is a safe test with no significant side effects, except for possible discomfort for the time required to perform the test, which may require some effort. It is contraindicated to perform the methacholine test in the case of recent myocardial infarction, known arterial aneurysms, severe hypertension, pregnancy, or epilepsy.

In the case of a positive result, the methacholine test reveals the presence of bronchial asthma, a respiratory disease characterized by chronic inflammation of the bronchi and alteration of regular airflow, causing respiratory problems, cough, or chest pressure.

Spirometry with methacholine at MiniHospital “Sandro Pertini”

MiniHospital “Sandro Pertini” has a state-of-the-art spirometer equipped with a cabin for administering methacholine to patients. The one used in the pneumology outpatient clinic coordinated by Prof. Dr. Pierluigi Paggiaro is a state-of-the-art machine capable of accurately measuring bronchial reactivity and gas exchange in the lung alveoli.

Spirometry with methacholine and respiratory rehabilitation

As mentioned earlier, the methacholine test is used to diagnose asthma, one of the most common chronic respiratory diseases.

At MiniHospital “Sandro Pertini,” a respiratory rehabilitation program is available to support patients with these types of conditions. Patients are helped to maintain their abilities and recover lost capacities due to the disease, bringing the patient back to a state of normalcy. A team of professionals follows each patient with a multidisciplinary approach to monitor symptoms and improvements day by day.

For rehabilitation activities, patients at MiniHospital “Sandro Pertini” have access to physiotherapy clinics equipped with state-of-the-art tools, a gym equipped with specific equipment, and a swimming pool suitable for individuals who need to exercise with either no or partial body weight. The respiratory rehabilitation program can be carried out on-site or at home for those with specific needs.

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