[Physical symptoms of Parkinson's disease and the score on Beck's Depression Inventory]

In patients with Parkinson's disease high prevalence of depression has been estimated. This prevalence may be overestimated since the commonly used assessment of depressive complaints neglects the correspondence with physical symptoms of Parkinson's disease and psychosomatic symptoms in depression. To evaluate the effect of this contamination, we presented a frequently used questionnaire for assessing depressive complaints, Beck's Depression Inventory (BDI), to eight neurologists specialized in Parkinson's disease. We asked them to select those items on which Parkinson patients might receive high scores merely because of the physical symptoms of their disease. Based on their consistent judgments, a BDI-version corrected for somatic items was constructed. Next, the scores of the original and the corrected version were computed for 27 outpatients with Parkinson's disease (from mild to very severe) and 52 psychiatric inpatients who were being treated for depression. Prevalence of depression were 74% (original BDI) and 48% (corrected BDI) for the Parkinson group and 75% and 81% respectively for the psychiatric group. Results indicate that great care should be taken in interpreting scores on depression inventories in patients with Parkinson's disease. In general, the results raise doubts on the validity of somatic complaints as indicators of depression in patients with Parkinson's disease.