Psychosis, in its broadest definition, refers to any major derangement in mental function in which the individual's ability to perceive and interact with the environment is impaired. Hallucinations are a frequent accompaniment but do not alone define this category of illness. From a neurologic perspective, there are four major categories of psychosis: (1) confusional-delirious states, (2) psychoses associated with focal or multifocal cerebral lesions, (3) affective disorders (bipolar and depressive psychoses), and (4) schizophrenia. The first two categories are discussed in Chaps. 20 and 22. The latter two are the subject of this and the following chapter.
Depression is perhaps the cause of more grief and misery than any other single disease to which humankind is subject. This view, expressed by Kline more than 40 years ago, is still shared by everyone in the field of mental health. The several forms of depression taken together are the most frequent of all psychiatric illnesses. In a general hospital, as indicated in the previous chapter, depression accounted for an estimated 50 percent of psychiatric consultations and 12 percent of all admissions. Although depression has been known for more than 2,000 years (melancholia is described in the writings of Hippocrates), there is still uncertainty as to its medical status as a disease state (kraepelinian concept) or as a type of psychologic reaction (meyerian concept). In other words, is it basically a biologic derangement or a response to psychosocial stress? An eclectic position is that both are correct—i.e., that there are two basic forms of depression: exogenous (an apparent cause) and endogenous (with no overt external cause), and that there may be both an interplay between them and biologic susceptibility to either one.
In respect to endogenous depression and the related condition of bipolar disease, genetic and neurochemical data cited further on support the kraepelinian view of a disease state. Nonetheless, a lay concept persists, perpetuated perhaps by some process-oriented psychiatrists, that events in one's life, either distant or current, underlie all types of depressive illnesses. An unfortunate consequence of this view is the assumption that an inability to deal with these stresses represents a personal failure of sorts and this in turn may inhibit the acceptance of psychiatric help.
Of considerable consequence for clinical work, depressive states are often associated with obscure physical symptoms. For this reason they are likely to come first to the attention of general physicians than are other psychiatric entities. All fields of medical specialty, however, have depressive equivalents; the physical symptoms frequently are mistakenly attributed to anemia, low or high blood pressure, hypothyroidism, migraine, tension headaches, chronic pain syndrome, or chronic infection, or are casually attributed to emotional problems, worry, and stress. Neurologists are most likely to encounter depressed patients who complain of fatigue and weakness, chronic headache, and difficulty in thinking or remembering. Depression masquerading as a chronic pain or a fatigue state or some other medical condition had been called masked depression or ...