ASSESSMENT OF DEPRESSION
Because depression is common and can temporarily fluctuate in patients with MS, healthcare providers must have the necessary tools to make timely and accurate diagnoses [62]. One difficulty in diagnosing depression in MS is that many depressive symptoms are observed in MS patients without mood disorders. For example, both fatigue and cognitive dysfunction associated with MS are common and must be considered by the provider in the differential diagnosis of depression. Although more rare, patients with MS can exhibit pathological laughter or crying that poorly correlates with the underlying mood. This syndrome of emotional lability typically occurs with bilateral forebrain disease [76]. Given the overlap of symptoms between depression and MS, the diagnosis of depression in patients with MS is often complicated. Therefore, researchers and clinicians have used psychometrically validated measures of mood to aid their differential diagnosis.
Historically, there have been two main theoretical frameworks for using validated instruments in the assessment of depression in people with MS. In the first framework, the main goal of assessment is to directly address the symptoms of depression. This is helpful when healthcare providers need to conduct rapid triage and diagnosis so that fast, directed treatment decisions can be made. The second framework looks at depressive symptoms in the context of other MS-related symptoms and emotional responses (e.g., fatigue, low self-esteem, anxiety) that affect overall QOL.
For the busy clinician, the U.S. Preventive Services Task Force recommends a brief two-question screening test for assessing depression (Figure 1) [77-78]. If the answer to one or both questions is positive, the patient should be assessed for the other seven DSM, Fourth Edition (DSM-IV) criteria for major depression. When using this two-question screening test, clinicians should recognize that some patients with MS demonstrate subsyndromal symptoms of depression or mood instability [79] that do not meet the criteria for major depression. These symptoms are nonetheless associated with significant distress and can respond to therapy. Thus, their detection with the two-question screening test would alert the clinician to the need for treatment. One should note that, despite its face validity, the two-question screening test is not yet validated for use with patients with MS. Thus, at present, it is preferable for clinicians to use an objective depression measure (discussed in the next paragraphs). Objective, validated self-report measures have been used in research on patients with MS, which provides at least some degree of validation. However, the two-question screening test may be useful for busy clinicians who have no time to administer objective measures and would otherwise forego more in-depth depression screening.
The BDI is one of the most commonly used objective self-report depression measures [50]. This inventory has a long history of proven validity for assessing depression in the general public. Though some researchers believe that use of BDI with patients with MS is valid [80], others believe that such use is inappropriate. One main argument against its use is the long administration time. For this reason, several studies have sought to develop questionnaires that assess depressive symptoms in a less time-intensive manner. An example is the Yale Single Question; however, it lacks sensitivity and failed to identify 35 percent of depressed MS patients who had been positively identified on the BDI [81]. Another argument against the use of the BDI with patients with MS is that, because of the high number of items that assess neurovegetative symptoms, it overdiagnoses depression in this population [15]. For that reason, a number of researchers have attempted to identify the BDI items that contain confounds between somatic MS symptoms and neurovegetative symptoms of depression. These studies have resulted in short-forms of the BDI [82]. The best validated BDI short form is the BDI-Fast Screen (BDI-FS). In a recent study, Benedict et al. validated the BDI-FS with patients with MS [83]. Data from the study supported the concurrent and discriminative validity of the BDI-FS, which indicates that the test did not confound MS-related neurological symptoms. The Chicago Multiscale Depression Inventory is an alternative short instrument that was developed for assessing depression in patients with MS [84]. It was found to have good internal consistency, sensitivity, and construct validity [4].
Based on the idea that a multifactorial approach is the most useful for obtaining a holistic picture of adaptation to MS, one movement in the MS field has been the development of a single multidimensional mood instrument. One such instrument is the Profile of Mood States (POMS), which measures mood and multiple dimensions of adaptation, including daily activities, fatigue, and disease status [85]. Unfortunately, although the scale composite score has been found useful, the subscales appear to be intercorrelated [86]. Therefore, the effects of mood relative to other factors cannot be teased apart. A more recently developed multidimensional scale is the Functional Assessment of MS (FAMS). The reliability and validity of the FAMS in patients with MS have been confirmed [87]. The FAMS is divided into six subscales: emotional well-being (depression), mobility, symptoms, general contentment, thinking/fatigue, and family/social well-being. In their comparison of multiple QOL measures, Nicholl et al. found that the FAMS was the most sensitive measure of the functional domains often associated with decreased QOL in MS patients [88]. In a study that assessed QOL among patients with MS in Spain, MS disability was related to emotional well-being (depression), mobility, and physical symptoms [89]. This study confirms that although depression is certainly a factor in adjustment to MS-related disability, other issues must also be considered and assessed. At this point, little data exist on the FAMS with respect to more global use in the MS community.
Although the best multidimensional tool for assessing depression in patients with MS is currently unclear, the tool must effectively and independently measure both fatigue and depression. Data indicate that depressive symptoms can independently predict fatigue severity [90], and improvement in depressive symptoms appears to be closely associated with decreased fatigue severity [91]. This interaction between depression and fatigue has significant implications for QOL. Research on QOL indicates that the effects of depression on the overall well-being of patients with MS cannot be fully understood without consideration of the presence and severity of fatigue [92]. Given that both depression and fatigue may independently affect [93] and predict [94] QOL, how depression affects the well-being of patients with MS cannot possibly be understood without an evaluation of fatigue. One should note that, in addition to measurement of fatigue, a thorough multidimensional assessment of QOL in depressed MS patients should include, at minimum, a screen of cognitive assessment. In the last few years, the complex interactions among depression, fatigue, and cognition have been repeatedly described in the literature [95-97]. In fact, depressed MS patients clearly perform worse than nondepressed MS patients on measures of cognition [98]. This has significant implications for depressed MS patients with respect to their ability to function in their daily lives. When attempting to refine and expand multidimensional QOL measures, researchers must understand that depression does not exist in a vacuum for patients with MS. Specifically, for such instruments to effectively portray the effects of depression on an MS patient's well-being, they must include items or scales that assess fatigue and cognitive function. Furthermore, multidimensional QOL scales should include some method for interpreting the interaction among depression, fatigue, and cognition. Only then can clinicians and researchers obtain a comprehensive picture of the QOL of depressed MS patients.