Case Reports and Case Series

Case reports and case series in epidemiology and medicine are a type of descriptive study based on singular or grouped uncontrolled observations of patients. Case reports are defined here as singular reports on one individual patient, while case series are collections of information on more than one patient. The subjects in a series usually share one or more common characteristics, such as disease, treatment, or side effect. Usually subjects are followed for a period of time to observe a particular outcome; however, for reasons often to do with convenience or practicability, series may be retrospective collections of patient histories. A series may also be purely descriptive of a point in time—for example, describing variations of clinical presentations. While some series are purely observational, case series can also be uncontrolled clinical trials of interventions, the most sophisticated of which are Phase I or II studies conducted by the pharmaceutical industry. Case [Page 135]reports and series are an important part of medical publishing due to their perceived methodological ease and observational character.

The number of patients in series is not limited, and large observational studies may be considered case series. This definition by logical extension would also include any series of clinical or physiological experiments in healthy or diseased subjects provided it is uncontrolled; however, in practice these investigations are usually not considered case reports or series.

While case series have no explicit comparison group, most have implicit comparisons, namely, a ‘normal’ clinical course or population. This comparison group may be mentioned or even quantified based on available clinical data.

The most undisputed and common usage of case reports is in clinical education. There they are used as a practical and easily available method to illustrate typical or unusual presentations or clinical courses. Most clinical teaching in medicine relies on cases discussed either informally during ward rounds, during more formalized conferences, or in publications.

Case reports and series are particularly valuable for the reporting of adverse events, where they are used to quickly alert the public to potential side effects of new interventions. Due to the limited number of patients exposed during the development of any clinical interventions, rare side effects usually cannot be detected; thus case reporting is essential in this area. Numerous guidelines have been developed to establish causal relationships in adverse event reporting. However, due to their anecdotal character, case reports and series of adverse events can lead to false-positive reporting. One example is Debendox (Bendectin), a drug that was licensed for pregnancyrelated morning sickness. After unsubstantiated reports of fetal malformations, the drug failed on the market, even though large studies refused a causal relationship between the drug and the birth defects.

Case series have been and are extensively used to inform the practitioner about the clinical presentations of diseases or syndromes. They inform about the frequency of signs and symptoms and are thus indispensable for clinical science. Case series may also be used to identify a new set of signs, symptoms, or clinical course as a new pathological entity or separate a clinical entity as a different disease or syndrome. The latter may be comparative and then does not fulfill our criteria. Exceptional case reports may also illuminate the pathophysiology of a particular condition and may overlap with basic science reporting.

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