The tyranny of rare diseases

摘要

There are a number of common respiratory diseases which on presentation resemble different and much less common disorders, many of which are lethal if untreated. Many of these conditions may present only once every year to every several years, and so the diagnosis is easily missed, or can be delayed until complications have arisen and the treatment and prognosis is much less certain. In our Department we have had a number of such conditions referred to us over the past few years. One such disease which occurs in asthma is Churg Strauss Syndrome (CSS), a systemic necrotizing vasculitis. A ten year study in the Norwich Health Authority of the United Kingdom found that the prevalence of Churg Strauss Syndrome (CSS) was 2.7 per million, or 3.4 per million, depending on the definition of the disease (1) When compared with the prevalence of asthma in adults (8.3%, or 83,000 per million) (2), it is easy to see how it can be missed. The solution is also not to screen for these diseases in every patient as a lot of unnecessary tests will be done, increasing cost and potentially morbidity of testing. Hence, one must be aware of factors that increase the pre-test probability of the diagnosis, factors colloquially known as "red flags".