Introduction

An accurate diagnosis is necessary, albeit not sufficient, for proper treatment and counseling of patients. According to Medline, the number of publications on the diagnosis of nervous system diseases has risen from almost 3500 in 1980 to more than 6000 in 1996. The proportion of papers on diagnostic innovations as measured by the percentage of papers containing adjectives such as “new,” “novel” or “promising” rose from 3 to almost 7% in the same period. Thus, both in absolute as well as in relative terms clinicians are confronted with a continuing proliferation of reports on new diagnostic technologies.

New diagnostic tests may have important implications for everyday clinical practice, for research into pathogenic mechanisms, and sometimes even for classifications of diseases. In neurology, the advent of magnetic resonance imaging (MRI) has affected the diagnostic approach to a wide range of clinical problems in a fundamental way. Neuroreceptor imaging with radioactive tracers fuelled speculation on pathogenesis of several diseases and sequencing of the prion protein gene resulted in the definition of the new nosological entity of “prion diseases” encompassing various neurodegenerative syndromes with a distinct clinical phenotype. These different kinds of developments as a result of diagnostic innovations make diagnostic research ever more important.

Kent and Larson have proposed a standardized approach towards evaluations of new diagnostic technologies. They distinguish five levels of benefit attributable to diagnostic testing (Table 5.1), and the hierarchical nature of their framework implies that positive effects at higher levels of evaluation require good results at preceding levels. However, good performance at one of the lower levels of evaluation does not guarantee utility at the higher, clinically more relevant levels of evaluation.