Differential diagnosis is the bread and butter of our task as clinicians. Most patients don't come to the office saying “I have Major Depressive Disorder . . . give me an antidepressant” (although some do!). More typically, the patient consults us with particular symptoms that are the source of clinically significant distress or impairment. Confronted with one (or a couple) of specific symptoms, it is our job to cull from the wide universe of DSM-IV-TR conditions those that could possibly account for them. Once we are armed with this initial list of possibilities, our next job is to collect additional information (from personal history, family history, mental status examination, or laboratory investigations) that will allow a winnowing down of the list to a single “most likely” contender, which becomes the initial diagnosis leading to the initial treatment plan. One must still keep an open mind, however. Confirmation of the initial diagnosis often requires the passage of time so that the telltale features of the course can play themselves out.
This handbook should improve your skill in formulating a comprehensive differential diagnosis by presenting the problem from a number of different perspectives. In Chapter 1, “Differential Diagnosis Step by Step,” we explore the differential diagnostic issues that must be considered in each and every patient being evaluated. In Chapter 2, “Differential Diagnosis by the Trees,” we approach differential diagnosis from the bottom up– that is, a point of origin that begins with the patient's presenting symptom(s). Each of the 27 decision trees indicates which DSM-IV-TR diagnoses must be considered in the differential diagnosis of that particular symptom and outlines the thinking process involved in choosing from among the possible contenders. In Chapter 3, “Differential Diagnosis by the Tables,” we approach differential diagnosis from a later point in the assessment process–that is, once you have reached a tentative diagnosis and want to ensure that all reasonable alternatives have received adequate consideration. This section contains 62 differential diagnostic tables, one for each of the most important DSM-IV-TR disorders. Chapter 4, “DSM-IV-TR Symptom Index,” includes a symptom index that lists in a convenient form those disorders that one should think of when formulating a differential diagnosis given a particular symptom in the patient's presentation. Finally, the handbook closes with the DSM-IV-TR Classification, which has been included to facilitate coding and to provide an overview of all of the diagnoses that must be considered in differential diagnosis.
The information provided in the decision trees, the differential diagnosis tables, and the symptom index is somewhat overlapping, but each format also has its own strengths and may be more or less useful depending on the situation. The decision trees highlight the overall algorithmic rules that govern the classification of a particular symptom. In contrast, the symptom index does not indicate any of the rules of association but does offer the greatest level of specificity by covering a wider range of presenting symptoms. The differential diagnostic tables have the advantage of providing a head-to-head comparison of each disorder and its nearest neighbors. Different readers will have different purposes and different methods of using this handbook. Some individuals will be interested in a comprehensive overview of psychiatric diagnosis and will find it rewarding to review the handbook cover to cover. Others will use the handbook more as a reference guide to assist in the differential diagnosis of a particular patient.
The art and science of psychiatric diagnosis is both cursed and blessed by the fact that individuals are ever so much more complex than the information laid out in any set of decision trees, tables, and indices. One must always temper the temptation to apply DSM-IV-TR or this handbook in a rote or cookbook fashion. The approaches outlined here are meant to enhance and not to replace the central role of clinical judgment and the wisdom of accumulated experience. On the other hand, clinicians who are not aware of the guidelines for differential diagnosis included in DSM-IV-TR may become idiosyncratic in their diagnostic and treatment habits. It is useful to know and use DSM-IV-TR but not be enslaved by it.