When you have excluded all possibilities, then what remains—however improbable—must be the truth.

—Sherlock Holmes


Often in medicine, it might not be trivial to arrive at the right diagnosis, because some conditions may have similar manifestations and because knowledge of them is not complete. In such cases, a reliable differential diagnosis is essential.
In respiratory medicine, distinguishing between asthma and chronic obstructive pulmonary disease (COPD) through an accurate differential diagnosis is of major importance. These two pathologies, both obstructive lung diseases, share common characteristics and manifestations, but their etiologies and the pathophysiology differ greatly. Thus, their prognosis, their treatments, and responses to therapy for them are different as well.
Until recently, COPD was identified with difficulty and only when the progression of the disease had caused organ damage and a great discomfort to the patient. When it was treated as if it were asthma, the situation only worsened. Nowadays, the first assessment of airway obstruction and the initial diagnosis are easier, thanks to the knowledge we now have of this condition and of new indications for a helpful differential diagnosis. Many factors have to be taken into account to distinguish between asthma and COPD: the patient’s medical history, physical examination findings, and the results of several tests. There are now questionnaires available that are based on scores or algorithms to help physicians diagnose COPD.
All of these tools make the diagnosis of COPD more precise, even though we are far from having an ideal test with a high specificity and sensitivity that make the diagnosis certain, with no doubts. Very difficult cases involve patients with features of both asthma and COPD. Because the phenotypes of individuals with overlap syndrome are variable, it is difficult to classify them and treat them appropriately. This monograph provides some suggestions to assist the clinician in arriving at the right diagnosis.
After initial identification of COPD, it is nevertheless very important to monitor patients and evaluate their response to treatment, in order to adjust their therapy according to outcomes and to ensure the best therapeutic option for each patient.
The article by David Price and coauthors in this issue of Hot Topics in Respiratory Medicine reviews the importance of differential diagnosis for COPD, with particular attention focused on the means by which this can be accomplished during the first evaluation of the patient. Suggestions on how increase the rate of successful diagnosis in primary care are also discussed.
The focus of the article by Marc Miravitlles is on the special case of overlap syndrome. The author discusses the prevalence and characteristics of these difficult phenotypes, illustrating the consequences for their management.