Introduction | Part 1: Hierarchy of Evidence | Part 2: Case Reports | Part 3: Cross-Sectional Studies | Part 4: Case Control Studies | Part 5: Cohort Studies | Part 6: Randomized Controlled Studies | Part 7: Meta-Analysis | Part 8: Systematic Reviews

Related: The Curbside Consultation | The Focused Clinical Question

Related: The Curbside Consultation | The Focused Clinical Question

Case reports or vignettes (see also case histories or case studies) are quantitative studies of individual patients. Case series are studies of patient groups. Interesting, rare, unusual, or novel patient conditions or outcomes about a single patient are published as a case report.

Formats vary, but in general they include relevant patient descriptive  information (i.e. demographic or signalment data). While HIPAA (U.S.) is not scoped to veterinary medicine, reports obviously deidentify protected health information about clients, but relevant non-identifying client information may be described (e.g. “the cat’s owner was a heavy and chronic smoker”). Past medical history, presenting complaint, clinical signs or symptoms, diagnostic evaluation with or without images or specific results may be included included as well as relevant follow-up care.

From 2000-2010, there were approximately 1.5 million human-related case reports in the medical literature as reported by publication type in MEDLINE* . By comparison there were only about 25,000 in the veterinary literature during this period. This represents about 18% of all publications (veterinary) while in human medicine it was approximately 35%. 

The top ten veterinary journals publishing the most case reports in descending order were JAVMA, Veterinary Record, Journal of Small Animal Practice, Canadian Veterinary Journal, Veterinary Pathology, Journal of Veterinary Medical Science, Journal of Veterinary Diagnostic Investigations, Australian Veterinary Journal and the Journal of the American Animal Hospital Association

The top ten major indexing terms (MeSH) among case reports were dogs, dog diseases, differential diagnosis, fatal outcome and treatment outcome, cats, cat diseases, horses, horse diseases and immunohistochemistry respectively (the last of which interestingly shares the 10th spot with the human literature). In dogs, most of these related to disease topics pathology, surgery and discussions regarding differential diagnoses.

By comparison, the top ten indexing terms in the human case report-related literature were treatment outcome, tomography (x-ray, computed), differential diagnosis, magnetic resonance imaging, young adult, follow-up studies, fatal outcome, biopsy, pregnancy and immunohistochemistry.

* Please note: These are preliminary and exploratory frequency statistics from a current research effort comparing publication types in human and veterinary medicine by the author.

A oversimplified case report workflow is as follows:

     Patient(s) Observations → Data from Medical Record/Progress Notes → Journal Article as a Case Study

Advantages:
Case reports have the ability to help identify  previously unknown adverse events or risks or novel treatments which can lead to further, more robust investigations. This especially holds true for conditions that are relatively rare and otherwise would not be noted in a controlled study where a finite number of patients are selected that represent a small subset of the entire population. For example, identifying and understanding adverse environmental health effects in a specific population may only become evident via a case report describing a worker or group of workers developing an unusual illness. 

On 5 April 2002, a case report of cutaneous anthrax was identified in a laboratory worker who was processing samples as part of investigations triggered by the bioterrorism events in the Fall of 2002. It was the first case associated with a laboratory evaluation in this investigation. Observations of unusual events, outcomes or presentations, as often described in case reports, assist researchers in moving forward towards a better understanding of these relationships with statistically valid research (see LINK case-control studies).

Disadvantages:
As mentioned above, case studies are at the bottom of the evidence hierarchy because they are anecdotal and experiential. Although assumptions are often made about cause and effect within a report, it largely remains unknown if what was observed can be easily explained. Also, the patient(s) in the report may not represent your target patient or the entire population in general. Can the results of a new intervention and an apparently successful outcome be causally related? Or were there other unknown interactions? Or were they simply due to the phenomenon of chance?

Another important concern in case reporting is publication bias. Reports that detail novel, interesting and especially positive outcomes tend to be submitted and/or accepted by publishers more readily than negative or less interesting cases.

Recommendation
Case reports and case series involve a limited number of patients and are unaware of causation as well as the efficacy of treatment vs. the natural history of disease. They use no controls or other statistical evaluation. They are simply a summary of the authors observations and actions regarding the reported case. Unless a reported observation is rare or poorly understood, seek evidence from more rigorous studies higher on the evidence ladder.

 

Example 1

Limb sparing using a double bone-transport technique for treatment of a distal tibial osteosarcoma in a dog; Rovesti GL, et al; Journal of Veterinary Surgery; 2002 Jan-Feb;31(1):70-7.  

[Pubmed| Closed Access | Mendeley]

This report described a novel double transport technique following tumor resection of a spontaneously occurring osteosarcoma in the tibia of an 11 year old German Shepherd Dog. Following two osteotomies with the tibia fixed within a frame, both bone segments were transfixed with wires and bone transport was performed until the distal segment made contact with the tarsus. This patient was also treated medically with a serial cisplatin protocol. A tibiotarsal arthodesis was performed 201 days after surgery. There was no local recurrence of the tumor, however the dog died of metastatic disease 239 days after the first surgery. The authors indicate that the cisplatin treatment “did not appear to negatively affect bone regeneration”. The outcome, in this case, was a reduction in treatment vs. a conventional single transport technique. Although the dog apparently lived an extended quality of life beyond expected survival of no treatment, it is unclear whether this technique played any role in the delay in metastasis, whether the lack of local recurrence was helped by the surgical procedure, was due to cisplatin alone, or the observations were the consequence of chance.

 

Example 2

Imaging of exogenous lipoid pneumonia simulating lung malignancy in a dog | Carminato A, Vascellari M, Zotti A, Fiorentin P, Monetti G, Mutinelli F. | Can Vet J. 2011 Mar;52(3):310-2.

[Pubmed | Full Free Text | Mendeley]

More Information:
There are journals dedicated solely to case reports. Case Reports in Medicine and the Journal of Medical Case Reports are both open access journals. Although they are dedicated to human medicine, one can learn about both the types of reports as well as their structure.  The journal "Case Reports & Clinical Practice Review" (2001-2007) was an international peer-reviewed journal dedicated to case reports and review articles. The types of case reports that were sought by this journal reveals some of the value of case reports in general:

  • Unusual presentation of unknown etiology
  • Unusual natural history / clinical course
  • Challenging differential diagnosis
  • Mistake in diagnosis
  • Unusual or unexpected effect of treatment
  • Diagnostic / therapeutic accidents
  • Unusual setting of medical care
  • Management of emergency care
  • Use of new medical technology
  • Patient complaints / malpractice

This series has been loosely organized from a set of lectures given by the author within graduate courses in Biomedical Informatics beginning in 2002. Content is being edited to improve organization, depth, correct inaccuracies as well as updates with new information during Winter/Spring 2012. Feedback is greatly appreciated. © 2011, Stuart Turner.