This is a cardinal feature of asthma at any age. There is a common misperception that asthma is predominantly a childhood disease. However, in a survey of elderly persons from four communities in the US, the prevalence of physician-diagnosed asthma was 4%, with another 4% having probable asthma (symptoms of asthma without a diagnosis).³ This is similar to other estimates that 7–9% of individuals over the age of 70 have asthma. New-onset asthma is most common in childhood, but it may occur at any age, even in the eighth and ninth decades of life. It is often under-recognized or misdiagnosed in the elderly. A proper evaluation of asthma symptoms can lead to early diagnosis, proper treatment, and avoidance of unnecessary emergency department visits and hospitalizations.^4,5

The Diagnosis of Asthma in the Elderly
Unfortunately, the diagnosis of asthma is frequently overlooked in the geriatric population. Some elderly patients are reluctant to admit their symptoms, or consider them a result of normal aging. Under-reporting of symptoms in the elderly may have many causes, including depression, cognitive impairment, social isolation, denial, and blaming of symptoms on other comorbid illnesses. Even when symptoms are reported, lung function testing to confirm the diagnosis is often not carried out.⁶

On the other hand, the diagnosis of asthma is frequently confused with chronic obstructive pulmonary disease (COPD),⁷ a disease usually, but not always, associated with cigarette smoking. Both are associated with symptoms of shortness of breath, wheezing, cough, sputum production, and airflow obstruction on pulmonary function testing. In one study of a group of elderly asthmatic patients (mean age of 73 years), only 53% of patients had been correctly identified as having asthma. Furthermore, 19.5% of patients were given the wrong diagnosis of COPD.⁷ These patients were more likely to have their onset of symptoms later in life and have greater degrees of disability.

The presence of airflow obstruction can be confirmed by spirometry showing a reduced forced expiratory volume in one second (FEV₁) and ratio of FEV₁/forced vital capacity (FVC). A ratio of less than 70% increases the probability of asthma in an elderly patient with asthma symptoms. A brisk response to a short-acting bronchodilator may demonstrate the second cardinal feature of asthma: reversible airflow obstruction (‘a responder’). When airflow obstruction is found in an elderly patient, attempts should be made to demonstrate reversibility following the inhalation of a short-acting beta adrenergic agent such as albuterol. Age is not a significant predictor of the acute bronchodilator response in asthma. Using American Thoracic Society (ATS) criteria (the post-bronchodilator FEV₁ increases by more than 12% and 200cc), the probability of asthma is significantly increased. Some experts feel this confirms the diagnosis of asthma.⁸ While the response to an inhaled bronchodilator is generally greater with asthma (16 versus 11%), many patients with COPD will also meet the ATS reversibility criteria on any given testing day. However, this response may not persist—52.1% of patients will change ‘responder’ status between visits.⁹ This makes the test less than reliable to confirm the diagnosis of asthma.^10,11 If complete reversibility of airflow obstruction is documented, COPD, a disease of fixed airway obstruction, is excluded. A brisk post-bronchodilator response enhances the post-test probability of asthma.

A negative bronchodilator response to a short-acting beta agonist, on the other hand, does not rule out a diagnosis of asthma. Population studies have shown that as many as 30% of patients with fixed airflow obstruction have a past history of asthma.¹² Often, treatment over time will improve lung function and, when documented by spirometry, a diagnosis of asthma can be confirmed. Measurements of the FEV₁ over time may offer the best way of making the diagnosis.

Fixed Airflow Obstruction in Elderly Asthmatics
In addition to bronchoconstriction, causes of airflow obstruction are mucous plugging, bronchial wall edema, inflammatory cell infiltration, airway smooth muscle hypertrophy, and subepithelial fibrosis. All of these architectural changes are collectively referred to as ‘airway remodeling.’ While some of these changes may be reversible with treatment, at some point they may become permanent, and this results in fixed airflow obstruction.

There is growing evidence that the airway function of young and middle-aged asthmatics declines at a greater rate than that of normal subjects.¹³ The rate of decline increases with increasing age and in those who smoke cigarettes. These effects are variable since not all individuals show a steeper rate of decline. A longer duration and severity of previous asthma are also important factors.^14,15 In one random survey of 1,200 elderly asthmatics over the age of 65 years, only one in five patients had normal pulmonary function (FEV₁ >80% predicted), while a similar number showed moderate to severe airflow obstruction (FEV₁ <50% predicted) after an inhaled short-acting bronchodilator.¹⁶ Since structural changes of emphysema are minimal in elderly asthmatics, airway remodeling is thought to be the main cause of fixed airflow obstruction.¹⁷

While distinguishing asthma from COPD may be very challenging, there are features seen in elderly asthmatics with fixed airflow obstruction that are distinct from COPD caused by cigarette smoking. When compared with patients with COPD of similar age, they have significantly more eosinophils in the peripheral blood, sputum, and bronchoalveolar lavage (BAL), and on bronchial biopsy have higher numbers of neutrophils in the sputum and BAL, have higher ratios of CD4+/CD8+ T cells infiltrating the airway, and have greater thickness of the airway basement membrane than patients with COPD.¹⁸ Other distinguishing features include higher levels of exhaled nitric oxide, lower emphysema scores on high-resolution computed tomography (CT) scans, and higher diffusing capacities. Since many of these tests are impractical, not available for widespread use, or not discriminatory enough for clinical use, the most recent American Thoracic Society (ATS)/European Respiratory Society (ERS) Statement on COPD stated: “Some patients with asthma cannot be distinguished from COPD with the current diagnostic tests. The management of these patients should be similar to that of asthma.”¹⁹

While the main diagnostic challenge with asthma in the elderly is distinguishing it from COPD, many current or former smokers have both asthma and COPD. Also, asthma in the elderly may be mimicked by, and often confused with, other diseases, such as congestive heart failure, chronic aspiration, gastroesophageal reflux, and tracheobronchial tumors.²⁰