Diagnostic accuracy. The effects of multiple aetiology and the degradation of information in old age.

We propose two causes of diagnostic inaccuracy in elderly patients: multiple aetiology and the degradation of clinical information. A single clinical event in an elderly person is often the result of several small and sometimes changing aetiological factors. Multiple aetiology is particularly common in the elderly because of impairment in a number of organ systems, loss of physiological reserve, and the increased exposure to stresses. Diagnostic errors arise first because clinicians tend to look for single, large and static explanations for clinical events, and second because the errors inherent in each step in diagnosis compound when there are multiple aetiological factors. These inherent errors are also greater in old people because of difficulties in a variety of measurements. We present a numerical analysis of this which suggests that failing to make a diagnosis when the disease is present or making a diagnosis when a disease is not present is likely to occur twice as often in old as in younger patients. We suggest that these problems can be countered by being aware of the phenomenon of multiple aetiology and the diagnostic traps arising from it, and by employing the most accurate and discriminating methods when investigating elderly people. These diagnostic difficulties mean that, when they are ill and require treatment, old people need prompt access to the best of investigative and therapeutic facilities.