The recently renewed emphasis on evidence-based medicine has lead to many improvements in clinical practice. One of the less well recognized changes brought about by this renewal of evidence-based thinking is a welcome re-definition of the role of the single case report.

In the usual hierarchy of scientific evidence, the randomised controlled clinical trial ranks as one of the highest forms of evidence, and the single case report ranks as one of the lowest. However, it is important to note that the single case report still serves several specific functions, many of which are essential for the advancement of medical science.

In 1958 Asher ¹ famously posed the question, Why are medical journals so dull? Several answers have been proposed, but certainly when The Lancet ² launched a section of peer-reviewed case reports in 1995 they emphasized that clinicians often learn from stories stories told at medical school or stories told by colleagues or patients.

Vandenbroucke ³ recently undertook a systematic consideration of the role of the case report, and concluded that case reports fulfil a number of specific needs. Some of these needs relate to the progress of medical science and others relate to education and quality assurance.

In the first instance, it is argued that case reports are well suited to the description of new diseases and to the recognition of side effects. The anecdotal form of the case report also lends itself easily to the study of mechanisms of disease and the development of novel aetiological hypotheses which may then be examined and refined by colleagues.

The importance of this role is supported by the belief that the advancement of science is dependent on the development of novel hypotheses, followed by attempts to disprove them. There are several examples of single case reports leading to significant advances in elucidating aetiology, including, for example, an early descripton ⁴ of a deletion on the short arm of the X chromosome which duly led to the identification of the gene for Duchenne muscular dystrophy.

Vandenbroucke ³ also emphasizes the role of the case report in elucidating issues relating to therapy and prognosis, noting, for example, that single case reports can provide clues about new indications for old drugs. Indeed, several different advances in therapeutics find their roots in single observations: Alexander Flemings discovery of the antibacterial effects of penicillin is one example.

The second category of needs fulfilled by the single case report relates to education and quality assurance.³ Several journals publish case reports aimed at medical students, trainees and clinicians engaged in continuing medical education. These are all designed to improve the overall quality of clinical practice and maintain appropriate standards of patient care.

The case report, however, has several limitations, and these must be clearly understood if the information contained in the report is to be used appropriately. Case reports are, by their nature, anecdotal, and tend to describe atypical clinical events, rather than typical ones.⁵ They are subject to several kinds of error, including measurement error and observer bias. There are also important ethical issues involved, and the need to preserve anonymity is balanced against the need to provide comprehensive clinical information. It is considered good practice to obtain informed consent from the patient prior to submitting the report for publication.

In conclusion, it is clear that case reports still have an important role to play in the advancement of medical practice. It is, however, important to recognize their limitations, and to critically examine each report on its own merits. There are three key questions that determine the value of any case report:

1. How important is the clinical issue?
2. How convincing is the argument?
3. How readable is the report?

One medical editor ⁶ notes that the element of surprise is an important component in case reports that detail the difference between the observed and expected clinical events. Often it is this element of surprise that highlights the unique feature of the case presented and emhasizes the proposed scientific importance of the observation. It is also this element of surprise that sustains the readers interest and can transform a mundane clinical anecdote into a memorable case report.

B Kelly
Psychiatric Unit,
Healthcare Hawkes Bay,
Omahu Road,
Hastings,
New Zealand.
Tel: + 64 6 8788109
Fax + 64 6 8781381
Email:[email protected]

References

1. Asher R. Why are medical journals so dull? British Medical Journal 1958; ii: 502-3
2. Bignall J, Horton R. Learning from stories The Lancets Case Reports. The Lancet 1995; 346: 1246
3. Vandenbroucke JP. Case reports in an evidence-based world. Journal of the Royal Society of Medicine 1999; 92: 159-163
4. Francke U, Ochs HD, de Martinville B, et al. Minor Xp21 chromosome deletion in a male associated with expression of Duchenne muscular dystrophy, chronic granulomatous disease, retinitis pigmentosa and McLeod syndrome. American Journal of Human Genetics 1985; 37: 250-267
5. Farmer A. The single case study. In: Critical Reviews in Psychiatry (2nd ed.) Brown T, Wilkinson G, eds. London: Gaskell, 2000
6. Fox R. Writing a case report: an editors eye view. Hospital Medicine 2000; 61: 863-864.