Understanding the Differential Diagnosis of COPD

There are many medical conditions that can be easily diagnosed with a blood test or physical exam. Others are not so simple. In some cases, there will be no single test or procedure that can either confirm or exclude the presence of an illness.

Chronic obstructive pulmonary disease (COPD) is a case in point. While various respiratory tests such as spirometry can confirm the signs of the disease, they cannot confirm the diagnosis on their own.

For this, a doctor would need to make what is called a differential diagnosis. This is a process wherein all other causes of the illness have been methodically excluded. Only when the process is complete can a COPD diagnosis be considered definitive.

Why a Differential Diagnosis Is Necessary

A differential diagnosis is vital to confirming COPD because it remains such an elusive illness. While COPD is predominantly associated with cigarette smoking, not all smokers have COPD, and not everyone with COPD is a smoker.

Moreover, the symptoms and expression of the disease are highly variable. For example, a person for whom spirometry tests are inconclusive can often have severe COPD symptoms. Alternately, someone with marked impairment can often manage with few, if any, symptoms.

This variability requires doctors to look at the disease differently. And, because we don't yet fully understand what triggers COPD, doctors need the safety net of a differential diagnosis to ensure the right call is made.

In the course of a differential diagnosis, some of the more common investigations would include asthma, congestive heart failure, bronchiectasis, tuberculosis, and obliterative bronchiolitis. Depending on the health and history of the individual, other causes may also be explored.

Asthma

One of the most common differential diagnoses of COPD is asthma. In many cases, the two conditions are virtually impossible to tell apart (which can make management difficult, since the treatment courses are extremely different). Among the characteristic features of asthma:

• The onset of disease generally occurs early in life (compared to COPD, which happens later in life).
• Symptoms can vary almost daily, often disappearing between attacks.
• A familial history of asthma is common.
• Allergies, rhinitis, or eczema can often accompany it.
• Unlike in COPD, airflow limitation is essentially reversible.

Congestive Heart Failure

Congestive heart failure (CHF) occurs when the heart is unable to pump enough blood through the body to keep things functioning normally. This causes the backup of fluids in the lungs and other parts of the body. Symptoms of CHF include a cough, weakness, fatigue, and shortness of breath with activity. Among the other characteristics of CHF:

• Fine crackles can be heard when listening with a stethoscope.
• Chest X-rays will show excessive fluid and dilation of the heart muscle.
• Pulmonary function tests will show volume restriction (as opposed to the airflow obstruction seen in COPD).

Bronchiectasis

Bronchiectasis is an obstructive lung disorder that can either be congenital (present at birth) or caused by early childhood diseases such as pneumonia, measles, influenza, or tuberculosis. Bronchiectasis can exist alone or co-occur alongside COPD. Among the characteristics of bronchiectasis:

• Large amounts of sputum are typically produced.
• The person will have recurrent bouts of bacterial lung infection.
• Coarse crackles can be heard with a stethoscope.
• Chest X-ray will show dilated bronchial tubes and thickened bronchial walls.
• Clubbing of the fingers is common.

Tuberculosis

Tuberculosis (TB) is a highly contagious infection caused by the microorganism Mycobacterium tuberculosis. While TB normally affects the lungs, it can spread to other parts of the body as well, including the brain, kidneys, bones, and lymph nodes.

Symptoms of TB include weight loss, fatigue, persistent cough, breathing difficulty, chest pain, and thick or bloody sputum. Among the other characteristics of TB:

• Disease onset can occur at any age.
• Chest X-rays will show lung opacities.
• Blood or sputum tests will confirm the presence of M. tuberculosis.
• The disease would typically be seen within the community or manifest as part of an outbreak.

Obliterative Bronchiolitis

Obliterative bronchiolitis is a rare form of bronchiolitis that can be life-threatening. It occurs when the small air passages of the lungs, known as the bronchioles, become inflamed and scarred, causing them to narrow or close. Among the other characteristics of obliterative bronchiolitis:

• It generally occurs at a younger age in non-smokers.
• There may be a history of rheumatoid arthritis or exposure to toxic fumes.
• A CT scan would show areas of hypodensity where the lung tissue has thinned.
• Airway obstruction, as measured by FEV1, may be as low as 16%.