Depression in Parkinson's disease: a psychosocial viewpoint.

We started this chapter by examining a simple psychological model that depression was a straightforward reaction to the severity of the physical impairment of Parkinson's disease, and that the relationship between the two factors was essentially linear. Because of the progressive nature of the disease, it followed that any such relationship would also be reflected in factors such as stage of illness and duration. As seen, however, the data have consistently failed to support such a simple reactive model. Examining the equivalent literature on other physical disorders revealed a remarkably similar picture suggesting that the model is largely inadequate in general, as well as in relation to Parkinson's disease. This inadequacy, however, should not be taken as evidence that psychological factors are unimportant. Rather, it suggests only that we need a more comprehensive model linking chronic disabling illness and depression. One revision suggested by the evidence was to consider nonlinear relationships, for example, between depression and stage of illness. Adopting a broader perspective, one may suppose that the risk of depression may change over the course of disease progression. For example, at the very beginning, diagnosis and the process of coming to terms with the fact of having a progressive and disabling illness may be sufficient to cause depression. Later in the course of the illness, progressive deterioration and increasing dependency may once again provoke depression. At any stage, a rapid deterioration (from whatever level) or the development or worsening of treatment complications may cause fresh concerns and require a fresh period of adjustment. Although the depression may be similar in each of these cases, the mediating psychological factor is different. In between these times, the individual may adapt to the illness and its consequences and show less vulnerability to depression. A further modification of the model is to consider the influence of multiple factors. While any one factor may individually predict depression only weakly, in combination, they may explain the observed pattern of depression more accurately. Although little evidence is available, there is the suggestion that a combination of physical and psychological factors may provide a clearer picture of depression severity. The final, major modification suggested is to view the broad consequences of the physical disease, rather than the severity of the symptoms themselves.(ABSTRACT TRUNCATED AT 400 WORDS)