Course Authors

E. Neil Schachter, M.D.

Dr. Schachter reports no commercial conflict of interest.

Estimated course time: 1 hour(s).

Albert Einstein College of Medicine – Montefiore Medical Center designates this enduring material activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

In support of improving patient care, this activity has been planned and implemented by Albert Einstein College of Medicine-Montefiore Medical Center and InterMDnet. Albert Einstein College of Medicine – Montefiore Medical Center is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

 

Learning Objectives

Upon completion of this Cyberounds^®, you should be able to:

 

With over ten million asthmatics in the United States, morbidity and mortality among asthma patients are worsening. Guidelines reflecting a new understanding of the pathogenesis of this common disease have been slow to become part of standard therapeutic practice.

In this conference we will discuss the diagnosis of asthma, with respect to these new guidelines, and next month we will focus on the clinical managment of asthma.

Introduction

Asthma is one of three major pulmonary diseases (emphysema, chronic bronchitis, asthma) for which airway obstruction is a central feature. The characteristics of airway obstruction that distinguish asthma are:

• Reversibility -- complete or incomplete -- occurring spontaneously or with treatment
• Airway inflammation
• Increased airway responsiveness to various stimuli

Let's review a case that illustrates some of these characteristics and suggests common approaches to diagnosis, but which presents itself in a manner that is often-overlooked.

Case

A 24-year-old securities analyst, K.P., presents with a three-month history of persistent cough. The symptom began in late November with a productive cough, but no fever, chills or other systemic complaints. The patient sought advice from his primary care practitioner who prescribed a seven-day course of clarithromycin (Biaxin). The productive nature of the cough abated, but the cough itself increased, frequently awakening K.P. at night.

Upon questioning K.P. notes that his cough was worse in cold weather, when he exerts himself, and when he finds himself in the presence of smokers. He frequently notes a burning sensation in his substernal area particularly in a dusty room or one with old carpeting. He describes himself as otherwise basically healthy, a non-smoker, without known allergies. He jogs seven to ten miles weekly, but, since his cough began, he has been unable to maintain this program. He has no unusual environmental exposures. He works in a clean non-smoking office and actually notes less coughing while at work. His physical examination is unremarkable. A chest X-ray is within normal limits, as are the complete blood count and blood chemistries.

Diagnosis

This patient's symptoms did not clearly fit the usual presentation of asthma. However, because the persistent chief complaint of a dry cough did not resolve over four to six weeks and because the patient's chest x-ray was normal, the diagnosis of cough variant asthma was suspected.

Cough variant asthma has been recognized as a specific presentation for asthma since the 1970's. While it is simply defined as asthma in which the predominant manifestation is cough and in which there is no overt wheezing, the diagnosis is often missed and the patient is repeatedly treated for a presumed non-resolving upper respiratory tract infection. Nearly 5% of adult asthmatics present as cough variant asthma.

The differential diagnosis includes:

• Post nasal drip (41%)
• Asthma (24%)
• Gastroesophageal Reflux (21%)
• Chronic Bronchitis (5%)
• Bronchiectasis (4%)
• Other (5%)(1)

It should also be noted that patients treated with angiotensin converting enzyme (ACE) inhibitors may develop a similar syndrome.(2)

Work-Up

A work-up to confirm the diagnosis of asthma in this patient would include taking a careful history to elicit the waxing and waning nature of the airway symptoms as well as the role of specific triggers in bringing on respiratory difficulty.

Triggers Suggestive of Asthma

• Allergens (pollens, molds, dusts, animals, seasonality)
• Viral infections
• Occupational irritants or allergens
• Environmental changes
• Stress
• Drugs (aspirin, beta blockers, NSAIDS)
• Food additives
• Cold air
• Exercise

While history remains the cornerstone of the diagnosis of asthma, pulmonary function testing helps to establish the airway obstruction associated with asthma, the severity of that obstruction (to be discussed in our next Cyberounds^® Pulmonary Medicine conference) and the reversibility of the lung function abnormalities.

Documentation of Airway Obstruction: Lung Function Testing

The diagnosis of airway obstruction can be quantified from the pulmonary function testing, which graphs flow against volume.

Figure 1. Tidal Breathing.

Individuals with airway obstruction have difficulty with exhaling air rapidly because their airways are narrowed. The consequence of this is illustrated in Figure 2 below, the so-called Maximum Expiratory Flow-Volume (MEFV) Manuever, which shows how a forced exhalation total lung capacity (the lungs fully inflated) describes airway narrowing. The forced expired volume in one second (FEV1) is a reflection of how much air a person can exhale rapidly in one second. When this value is reduced (as below compared to predicted) or, more specifically, if the FEV1 represents significantly less than the anticipated 80% of the forced vital capacity (the total amount of air that can be exhaled) then obstruction exists.

Figure 2. Maximum Expiratory Flow-Volume (MEFV) Maneuver.

	Baseline	Post B/D	% Change	Predicted
		(Bronchodilator)
FVC	4.5L	5.3L	23%	5.3L
FEV1	3.2 L	4.2 L	31%	4.5L
FEV1%	71%	79%		85%
FEF50	3.0L/sec	4.0L/sec	53%	5.5L
FEF25	1.5L/sec	2.0L/sec	33%	2.5L
PEF	7.0L/sec	8.8L/sec	26%	9/6L

The standard for reversibility following bronchodilator used to confirm the diagnosis of asthma is that of the American Thoracic Society which calls for an increase of 12% in either FVC or FEV1 following bronchodilator administration.(3)

If criteria of reversibility are not met as above, and the question of asthma is in doubt, measurements of airway reactivity are frequently performed.

Documentation of Airway Hyperreactivity

Although everyone's airways may exhibit bronchospasm to a wide variety of irritant stimuli, asthmatics generally show airway hyperresponsiveness (response to much lower concentrations of an irritant). This increased responsiveness to low concentrations of irritants can be quantitated by provocation testing, a useful study for diagnosing asthma.

These challenge tests consist of measuring pulmonary function before and after inhalation of sequentially greater concentrations of a constrictor agent (e.g., acetylcholine, methacholine, histamine).

Figure 3. Acetylcholine.

Figure 4. Methacholine.

Figure 5. Histamine.

The most commonly measured pulmonary function test (PFT) parameter is the FEV1 and the extrapolated value measured is the PC20FEV1 or provocative concentration which causes a 20% reduction in FEV1 (Figure 6 .

Figure 6.

Summary

Asthma is a common disease of the airways. It is characterized by widespread airway obstruction, reversibility of this obstruction and airway hyperresponsiveness. While clinical features are often characteristic, the disease can present with unusual features. Lung function and provocation testing are helpful in confirming the diagnosis and assessing the severity of the obstruction.