Evaluating anecdotes and case reports.

Stories are more memorable than statistics. Newspaper or magazine articles about some new chemotherapy for cancer typically will include an interview with a patient who is doing well on it. Websites of alternative practitioners and clinics sometimes feature stories by or about patients describing their successful treatment. These stories can be very persuasive to readers, but some scientists dismiss them scornfully as “anecdotal” and therefore meaningless. Case reports, which have been published in the medical literature for decades, are also stories—they are descriptions of individual patients with unusual presentations or outcomes. What distinguishes an anecdote from a case report? As one author puts it, “The term ‘anecdotal evidence’ connotes secondhand or poorly documented fact and should not be confused with case studies of individual patients that involve careful observation and recording of detail.” Anecdotes and case reports cannot be used to definitively prove a therapy is effective. But case reports cannot be dismissed entirely. As a recent article stated, “Case reports and series have a high sensitivity for detecting novelty and therefore remain one of the cornerstones of medical progress; they provide many new ideas in medicine.” Case reports are a way to reveal the unknown or describe the previously unrecognized. They were critically important in the discovery of new diseases such as AIDS or Lyme disease. Descriptions of sick birds and sick people helped scientists figure out that West Nile virus had arrived in New York City, far from its usual location. Case reports are the first steps in discovering unexpected drug effects, both good and bad. For example, sildenafil (Viagra) initially was developed as a treatment for angina, but a side effect observed in individual cases led to its marketing as a treatment for erectile dysfunction. Case reports led to the discovery of heart problems caused by drugs that were prescribed to suppress appetite and muscle problems caused by contaminants in L-tryptophan. A well-written case report should provide clear evidence of the patient’s problem or condition and its treatment. In addition, it should provide a clear explanation of why the reader should be surprised by the outcome of the case, with appropriate references. CLEAR EVIDENCE OF THE PATIENT’S INITIAL PROBLEM OR CONDITION Because I work primarily with a nutritional therapy for cancer, I will use cancer as an illustration throughout this piece, though the principles can be applied to other illnesses. It is not uncommon to read patient testimonials that claim a diagnosis such as cancer was made but do not provide evidence that cancer was present. For example, I have seen cases where a patient found a breast mass, was told by a doctor that it was “clearly cancer,” refused surgical removal or biopsy, proceeded with some form of alternative therapy, and subsequently claimed miraculous cure. The problem with this scenario is that only a pathologist viewing a tissue sample under a microscope can diagnose cancer. It requires removal of tissue by biopsy or excision, or collection of samples for cytology. A doctor’s clinical impression of cancer or a suspicious test result does not prove the presence of cancer. As an example, in one study on the predictive ability of mammograms, lesions described as “highly predictive of malignancy” had an 81% chance of being found to be cancer when biopsy was performed— so 19% of the time, no cancer was present. In a case report, then, it should be clear exactly how the diagnosis was made. It should also be clear what treatment a patient might have received before embarking on the treatment that is being credited with an unusual outcome.