Listen: the patient is telling you the diagnosis.
Sir William Osler, Canadian physician (1849–1919)
Clinical assessment is every top clinician’s foundation stone and it is a complex skill. Its three goals are to:
determine the diagnosis of the patient
identify appropriate treatment mechanisms specific to that condition, and
build a professional, interpersonal relationship with the patient to guide efficient management.
Differential diagnosis is used to identify the pertinent diagnosis (condition) of the patient and is the focus of this chapter. This chapter should be read together with Chapter 15.
Differential diagnosis is a systematic process used to identify the proper diagnosis from a competing set of possible diagnoses. The diagnostic process involves identifying or determining the aetiology of a disease or condition through evaluation of patient history, physical examination, and review of laboratory data or diagnostic imaging; and the subsequent descriptive title of that finding.1
WHY IS DIFFERENTIAL DIAGNOSIS IMPORTANT?
Failure to correctly identify an appropriate diagnosis can lead to negative patient-reported outcomes,2 delays in appropriate treatment,1 and unnecessary healthcare costs.3
What makes diagnostic tests inaccurate?
failure to order appropriate tests (58% of instances)
inadequate history/physical examination (42% of instances)
incorrect test interpretations (37% of instances).4
With respect to medical errors, diagnostic errors are the most commonly recorded type (29% of all errors) and account for the highest proportion of total payments (35%).5
Differential diagnostic errors result in death or disability almost twice as often as other error categories.
Although the exact prevalence of diagnostic error remains unknown, data from autopsy series spanning several decades conservatively and consistently reveal error rates of 10–15%.6
DIFFERENTIAL DIAGNOSIS: A THREE-STEP PROCESS
Regardless of treatment environment, most clinicians follow a three-step questioning process during diagnostic assessment.7
The first question of diagnosis involves the query of whether the patient’s symptoms or emergent injury are reflective of a visceral disorder or a serious or potentially life-threatening illness. It is critical to be able to differentiate patients with symptoms that arise from a potentially life-threatening pathology or a non-mechanical disorder (i.e. referred pain).
The second question of diagnosis involves determining from where is the patient’s pain arising? This step has three substeps that involve: a. ruling out a location; b. ruling in a location but not knowing the tissue-related structure; and c. confirming the tissue-related structure that is causal. Although it is assumed that one can make an accurate tissue-related diagnosis, it is well known that differentiating tissue in the low back, shoulder, abdomen and hip is very challenging and it is not uncommon to see clinicians treat these areas without full knowledge of the tissue of origin. We will discuss ...