Initial Evaluation and Differential Diagnosis

The differential diagnosis of depression is organized along both symptomatic and causative lines. Symptomatically, major depression is differentiated from other disorders by its clinical presentation or its long-term history. This is, of course, the primary means of distinguishing psychiatric disorders in DSM-1V. The symptomatic differential of major depression includes other mood disorders such as dysthymic disorder and bipolar disorder, other disorders that frequently manifest depressed mood including schizoaffective disorder, schizophrenia, dementia, adjustment disorder, and post-traumatic stress disorder, and, finally, other nonpsychiatric conditions that resemble depression such as bereavement and medical illnesses like cancer or AIDS. 

The cause of most psychiatric disorders including depression remains unknown nevertheless, some diagnostic considerations are based on presumed causative factors. In these cases, the distinction from major depression is not based on the symptomatic presentation because there may be no symptomatic difference. The difference lies in the presence of an identifiable biological factor that is presumably causing the depressive syndrome. The causative differential of MDD includes a mood disorder due to a general medical condition in medically ill patients and a substance-induced mood disorder in patients using certain medications or substances of abuse. A comprehensive evaluation of depression must include consideration of potentially treatable causative factors. 

Dysthymic Disorder. Dysthymic disorder differs from MDD by being more chronic and less severe. Yet, two issues can cloud the distinction. First, some patients experience double depression in which an episode of major depression is superimposed on dysthymia. This can make it difficult to assess treatment response when the baseline mood is dysthymia instead of a normal euthymic mood. Second, a few patients may experience a chronic major depressive episode, which, like dysthymic disorder, lasts 2 years or more. In contrast to dysthymic patients whose insidious onset of symptoms leaves them unable to say exactly when the depression started, most patients with chronic major depression can tell when their depression began. 

Bipoiar Disorders. You must also distinguish the bipolar disorders from MDD. The distinction is particularly important in young adult patients given that nearly 10% of patients with an initial episode of major depression will go on to develop a bipolar illness. The devastating consequences of untreated mania coupled with the possibility that antidepressants may trigger manic episodes in susceptible individu- 

A number of medical conditions are associated with high rates of depression (see Table 3.4). In some instances, the distinction between MDD and depression due to a general medical condition is largely academic with little bearing on treatment selection. For example, pancreatic cancer may induce depression directly through the release of tumor-secreted substances however, depression in the pancreatic cancer patient is treated with conventional antidepressant medications. In other cases, the diagnostic distinction bears important treatment implications. One commonly cited example is depression occurring in association with hypothyroidism. Patients with depression and hypothyroidism do not respond to antidepressant treatment alone but require a thyroid hormone supplement. 

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INITIAL EVALUATION AND DIFFERENTIAL DIAGNOSIS 10.4.1 Initial Evaluation... 

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