There are no reliable and empirically derived criteria for recognition of depression in PD. Therefore, it is not surprising that depression remains under-detected and under-treated in the PD population (15,71). In a clinic-based study, nearly two-thirds of patients with clinically significant depressive symptomatology were not receiving antidepressant therapy (11). Older individuals often underreport depressive symptoms and are likely to focus on somatic or vegetative complaints (e.g., fatigue or loss of energy, reduced sexual desire or functioning, pain, sleep changes, or appetite changes), which are the prominent features of mood disorders as well as PD (102). Patients may simply attribute any mood symptoms to their PD, even when their PD has been relatively stable and the mood changes are relatively acute. In one study, over half the patients who had clinically significant depressive symptoms did not consider themselves depressed (11).
In a clinic-based study, the detection of depressive symptomatology in patients with PD more than doubled (21-44%) when patients were screened using the Beck Depression Inventory (BDI) (15). The assessment and recognition of depression has been ranked highly as an indicator for improving care of PD patients (103). All PD patients should be screened periodically to detect clinically significant depressive symptomatology. If self-reported disability is out of proportion to findings on the neurologic exam, depression should be suspected (73). Caregivers or family members are often valuable sources of information about the patient's psychological well-being, especially when self-report may be unreliable (104).
The DSM-IV diagnostic criteria for major depression includes the persistent presence of five of the following nine symptoms: anhedonia, depressed mood, diminished ability to think or concentrate, fatigue or loss of energy, feelings of worth-lessness or inappropriate guilt, insomnia or hypersomnia, psychomotor agitation or retardation, recurrent thoughts of death, and significant weight gain or loss (36). However, because several of these symptoms overlap with features of PD, the assessment of depression in patients with PD is not always straightforward. This is highlighted by a study demonstrating that anergy, early morning awakening, and psychomotor retardation are common and similarly frequent in both depressed and nondepressed patients with PD (105).
Clinician-completed symptom rating scales can be used as a screening tool to provide a measure of symptom severity or response to treatment. Examples include the Hamilton Depression Rating Scale (HAMD) and the Montgomery-Asberg Depression Rating Scale that have been validated for use in the PD population (70,106-108).
Despite the issue of separating out the somatic complaints of depression from underlying medical illnesses or consequence of aging, key psychological symptoms of depression, such as sad mood or frequent tearfulness, decreased interest in normally pleasurable activities or social avoidance, difficulty in making decisions or planning daily activities, feelings of worthlessness or hopelessness, and recurrent thoughts of death or suicide, are less affected by age or comorbid medical conditions and may be more helpful in reaching an accurate diagnosis. The United States Preventive Services Task Force (USPST) has recommended screening for depression in all adults, regardless of medical comorbidities (109). For routine clinical purposes, the USPST recommends asking the patient two questions: "Over the past two weeks, have you felt down or hopeless?" and "Over the past two weeks, have you felt little interest in doing things?" A "yes" to either question is a positive screen and warrants additional investigation.
Patients may also complete standardized, self-report instruments that are easily and rapidly administered in the outpatient setting and can be scored by physicians or allied health professionals. Several instruments are available, such as the BDI, Geriatric Depression Scale (GDS), HADS, Zung Self-Rating Scale, and the Center for Epidemiologic Studies Depression Scale (38,110-113). Although the 21-item BDI contains several somatic items, it has been determined to be a valid and internally consistent instrument for screening depression in the PD population if the cutoff score is modified. A cutoff score of 13/14 or 14/15 has been suggested for maximum discrimination between depressed and nondepressed patients with PD (114-116). Instruments that are free of somatic items include the 30-item GDS (GDS-30) (111), the 15-item GDS (GDS-15) (117), and the 7-item depression component of the HADS (38). The GDS-30 and GDS-15 have also been found to be reliable and valid for use in the PD population (108,118). In one study, sensitivity and specificity analyses showed that GDS-30
cutoff scores of 8/9 or 9/10 could be useful for screening of depression and 14/15 or 15/16 for diagnostic purposes in patients with PD (118). For the GDS-15, a cutoff score of 4/5 is associated with high discriminant validity for distinguishing depressed from nondepressed patients in PD. Its test characteristics were found to be comparable to that of the HAMD (108). The HADS has also been validated for use in the PD population (39). A 12-item short-form BDI, which excludes somatic items, has also been used to assess depression in PD but has not been psychometrically validated for PD (119). Overall, self-report instruments may be an effective means of screening for depressive symptomatology in patients with PD.
A physical examination and laboratory screening (e.g., complete blood count, liver function, serum testosterone level, serum vitamin B12, thyroid function) may be performed to exclude potential systemic causes of depressive symptomatology. Testosterone deficiency associated with depressive symptomatology (e.g., anhedo-nia, fatigue, and sexual dysfunction) has been described in males with PD and may possibly be managed with testosterone replacement therapy (120). Likewise, symptoms of hypothyroidism (e.g., anxiety, difficulty with concentration, dysphoria, fatigue, irritability, and motor retardation) resemble depressive symptomatology and are treatable with thyroid replacement. It is also important to ensure that patients are on optimal doses of antiparkinson drugs to minimize motor fluctuations that may contribute to mood fluctuations.
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