What’s known as the Asthma-COPD overlap syndrome was reviewed recently in the Allergy and Asthma Proceedings.

The authors adroitly point out that even though physicians try to pigeon-hole diagnoses, many times people’s health problems don’t fit neatly into a single diagnostic category. This is especially true in the spectrum of chronic airway disorders.

More and more people are being seen by physicians who have both asthma and COPD. The conditions are both similar and different.

In general, asthma (also called reversible airways disease — RADS) is completely reversible with therapies, while COPD (chronic obstructive pulmonary disease) is never (by definition) completely reversible; hence, the adjective “chronic.”

Both conditions are caused by inflammation in the airways. In asthma, the inflammatory cell is the eosinophil, while in COPD it is the neutrophil.

Both conditions tend to have genetic links. In asthma it is the genes that cause allergy. In COPD it is the genes that control alpha-1-antitrypsin (an enzyme that protects the lungs from oxidative stresses).

In general, asthma tends to have onset in childhood, whereas COPD occurs in adults.

Asthma is caused primarily by allergy to inhaled pollens, molds, danders and dust mites. COPD is caused primarily by cigarette smoke and biomass pollutants.

Finally, diffusion capacity is normal or high in asthma, but always reduced in COPD. Diffusion capacity is a measurement of the transfer of oxygen from the lungs into the blood stream.

The most important take-home message is that therapies that were previously used exclusively for one diagnosis may work in both because of the overlap. For instance, inhaled steroids which are a mainstay in the treatment of asthma often benefit patients with COPD.

Also, anticholinergics such as Atrovent, Combivent and Spiriva – originally designed exclusively for COPD – may also benefit people with the overlap syndrome. The bottom line is for patients and physicians to be aware of the overlap, and to look for therapies that are individually stylized to a given person’s need.