Differences in psychomotor activity in patients suffering from unipolar and bipolar affective disorder in the remitted or mild/moderate depressive state

Abstract

Background

Abnormalities in psychomotor activity are a central and essential feature of affective disorder. Studies measuring differences in psychomotor activity between unipolar and bipolar disorder show divergent results and none have used a combined heart rate and movement monitor for measuring activity during free-living conditions.

Objective

To compare objectively measured psychomotor activity in patients with unipolar and bipolar disorder in a remitted or mild/moderate depressive state. Further, both groups were compared to a healthy control group.

Methods

A cross-sectional study of outpatients suffering from unipolar (n = 20) and bipolar (n = 18) disorder and healthy controls (n = 31), aged 18–60 years. For three consecutive days a combined acceleration (m/s²) and heart rate (beats per minute) monitoring was used in conjunction with a step test to estimate activity energy expenditure (J/min/kg) as measures of psychomotor activity and physical fitness.

Results

Overall score on Hamilton-17 items ranged between 0 and 22. Patients had higher sleeping heart rate (p < 0.001), lower fitness (p = 0.02), lower acceleration (p = 0.004), and lower activity energy expenditure (p = 0.004) compared to controls. Comparing unipolar and bipolar patients and adjusting for differences in Hamilton-17 revealed lower acceleration (p = 0.01) and activity energy expenditure in bipolar patients (p = 0.02); the difference was most prominent in the morning.

Conclusions

Electronic monitoring of psychomotor activity may be a promising additional tool in the distinction between unipolar and bipolar affective disorder when patients present in a remitted or depressive state.

Introduction

Since the introduction of the dichotomy of unipolar and bipolar disorder by Perris (1966) it has been debated whether unipolar and bipolar affective disorders are categorically distinct diseases or dynamic diseases within a continuum (Benazzi, 2005, Holsboer, 2005). It is of crucial importance to be able to discriminate unipolar disorder from bipolar disorder in clinical practice, as pharmacological and psychological treatments as well as course of illness and outcome differ between the two disorders (Kessing, 1999, Kessing et al., 1998, Kessing et al., 2004). When patients present in a remitted or depressive state it may be difficult for clinicians to reveal whether they suffer from a unipolar disorder or from a bipolar disorder. Patients may not recall or may even deny prior hypomanic or manic episodes and clinicians may not be sufficiently observant on the prior course of illness. In this way, the diagnosis of bipolar disorder may be overlooked. Questionnaires such as the Hypomania Checklist (Angst et al., 2005, Bech et al., 2011) and rating scales such as the Bipolar Depression Rating Scale (Berk et al., 2007) have been developed to help clinicians to identify prior hypomanic episodes and even to differentiate bipolar depression from unipolar depression. Nevertheless, such measures based on the patient's subjective experience are influenced by depressive recall bias or other recall distortions (Moffitt et al., 2010). Consequently, it would be helpful for clinicians to add an objective measure that can help to discriminate between the two disorders based on the current state of illness.

Abnormalities in psychomotor activity are a central and essential feature of affective disorder and have been addressed in a number of studies (Beigel and Murphy, 1971, Kuhs and Reschke, 1992, Kupfer et al., 1974, Sobin and Sackeim, 1997). Psychomotor activity consists of multiple domains such as gross motor activity, body movements, speech and motor response time (Sobin and Sackeim, 1997). Most studies in psychomotor activity are based on clinical assessments or questionnaires showing divergent results (Blackburn, 1975, Dunner et al., 1976, Perris, 1966, Popescu et al., 1991, Salvatore et al., 2008). Similarly, physical activity questionnaires generally have a poor validity due to recall bias (Wareham et al., 2002). A few older studies have objectively measured the level of activity in patients suffering from affective disorder using wrist-worn accelerometers; all of them including only few patients and showing inconclusive results (Foster and Kupfer, 1975, Kuhs and Reschke, 1992, Kupfer et al., 1974, Popescu et al., 1991, Wolff et al., 1985). Studies using objective measures of activity included only hospitalised patients, but measuring psychomotor activity during hospitalisation would not give an indication of the habitual level of physical activity during free-living, and it cannot be compared to a healthy control group living under other circumstances.

The reference method for measuring energy expenditure during free-living circumstances is the doubly labelled water technique (Speakman, 1998). However, this method cannot quantify subcomponents of activity patterns such as hourly variation of movement, intensity etc. No study in unipolar and bipolar patients so far has combined accelerometry with a heart rate measurement (Kuhs and Reschke, 1992, Kupfer et al., 1974), a method which has been suggested to offer greater measurement precision (Brage et al., 2004).

Furthermore, psychomotor activity may be correlated with other mood symptoms (Sobin and Sackeim, 1997), but studies comparing psychomotor activity in unipolar and bipolar patients have not adjusted the analyses for differences in mood symptoms, e.g. a score based on the Hamilton Depression Scale. More specifically, results from some studies suggest that bipolar depression is more likely to manifest with psychomotor retardation and other atypical symptoms compared to unipolar depression (Beigel and Murphy, 1971, Kupfer et al., 1974, Mitchell et al., 2008, Nelson and Charney, 1980). Additionally, patients suffering from unipolar affective disorder with psychomotor inhibition are reported to be at increased risk of a later bipolar course (Akiskal et al., 1983). Concordantly, although the evidence is poor, reviews suggest that psychomotor retardation is more prevalent in bipolar patients (Goodwin and Jamison, 1996, Mitchell et al., 2008) and psychomotor retardation in bipolar disorder patients has been suggested as a signature symptom (Mitchell and Malhi, 2004).

The objectives of this study were to assess the psychomotor activity using combined heart rate and movement monitoring over three days in patients suffering from unipolar disorder and patients suffering from bipolar disorder in a remitted or mild/moderate depressive state and to assess differences between these patients. Further, both groups were compared to a healthy control group.