The GDS-15 is a commonly used instrument for depression screening in the general geriatric population and has been piloted for use in PD as well.31
Its clinical use in identifying depressed patients and its usefulness as a research tool for dPD, however, are predicated on the assumption that the GDS-15 is a valid measure of depression in this population. We evaluated the psychometric properties of the GDS-15 against the “gold standard” of DSM–IV
criteria for a depressive disorder and compared its performance in a PD population with the performance of a previously validated rating scale, the HDRS.10,32
ROC analyses revealed that the two scales had similar and high discriminant validity (i.e., good sensitivity and specificity) for a DSM–IV
diagnosis of depression. In this particular sample, the HDRS performed comparably to that reported in previous PD studies in dichotomizing depressed from nondepressed patients, although the optimal cutoff points were lower in our sample.10,32
Most significantly, our results suggest that the GDS-15 is as good as the HDRS at discriminating between depressed and non-depressed patients with PD with the GDS-15 correctly diagnosing a similar percentage of patients to the HDRS at the optimal cutoff points. As a screening instrument, the GDS-15 performed as well as the HDRS with high sensitivity and NPVs at the same cutoff scores identified for optimal dichotomization.
The similarity in performance of these two instruments points again to the ambiguities in the contribution of somatic and neurovegetative symptoms to the diagnosis of depression in diagnoses of dPD.26–28
Although the GDS-15 is a much shorter and less time-intensive instrument than the HDRS, it was also designed specifically for an elderly population. Thus, its treatment of symptoms common in nondepressed geriatric patients is modified, taking into account the potential influences of comorbid medical conditions, cognitive impairment, vegetative symptoms, and thoughts of death and the future that can occur in elderly patients without depression. In contrast with the HDRS, sleep, appetite, gastrointestinal symptoms, autonomic symptoms, and sexual symptoms are not assessed in the GDS as a result of their low correlation with the total GDS score.33
Therefore, although the HDRS is possibly a more comprehensive evaluation of depressive symptomatology, it may be the case that the GDS-15 succinctly targets the critical symptoms of depression in the PD population.
A practical way to implement routine screening for depression is important in this population, because there is evidence that dPD is underrecognized and undertreated.7,8
In addition, some patients with PD may be unaware of being “depressed” despite endorsing clinically significant depressive symptoms,34
and others may appear to be withdrawn or depressed by observers but not endorse symptoms of depression,35
so it is clearly necessary to have a validated instrument for depression in this population.
This validation of the use of the GDS-15 in PD both as a screening instrument and in discriminating depressed and nondepressed patients is of clinical significance, because it is a brief instrument that can easily be used in routine clinical care either as a self-or rater-administered instrument. The optimal cutoff scores for discriminating both major and minor depression from no depression also performed very well in discriminating either type of diagnosis individually from a nondepression diagnosis, indicating that the GDS-15 can be a sound clinical tool in identifying depression of either severity with the same cutoff.
Although the HDRS and MADRS also have high discriminant validity in PD, they are lengthy and rater-administered, requiring significantly more time for training and administration. The BDI, although relatively brief, can only be self-administered and does not adequately discriminate between depressed and nondepressed patients with PD.14
One limitation of this study was its use of a nearly all male and geriatric population, limiting the generalizability of the findings. In addition, the GDS-15 was both self- and rater-administered, and limitations in the data set did not allow us to determine which method was used at an individual level.
Our results suggest that the GDS-15 is valid for use in discriminating depressed from nondepressed patients with PD. As a result of its ease of use and good test characteristics, the GSD-15 is appropriate for routine use in the clinical care of patients with PD as well as for research purposes. Because depression is underrecognized and undertreated in this population, more widespread use of the GDS-15 could potentially lead to improved treatment, outcomes, and quality of life for dPD patients.