Abstract
Major depression occurs at high prevalence in the general population, often starts in juvenile years, recurs over a lifetime, and is strongly associated with disability and suicide. Searches for biological markers in depression may have been hindered by assuming that depression is a unitary and relatively homogeneous disorder, mainly of mood, rather than addressing particular, clinically crucial features or diagnostic subtypes. Many studies have implicated quantitative alterations of motility rhythms in depressed human subjects. Since a candidate feature of great public-health significance is the unusually high risk of suicidal behavior in depressive disorders, we studied correlations between a measure (vulnerability index [VI]) derived from multi-scale characteristics of daily-motility rhythms in depressed subjects (n = 36) monitored with noninvasive, wrist-worn, electronic actigraphs and their self-assessed level of suicidal thinking operationalized as a wish to die. Patient-subjects had a stable clinical diagnosis of bipolar-I, bipolar-II, or unipolar major depression (n = 12 of each type). VI was associated inversely with suicidal thinking (r = –0.61 with all subjects and r = –0.73 with bipolar disorder subjects; both p<0.0001) and distinguished patients with bipolar versus unipolar major depression with a sensitivity of 91.7% and a specificity of 79.2%. VI may be a useful biomarker of characteristic features of major depression, contribute to differentiating bipolar and unipolar depression, and help to detect risk of suicide. An objective biomarker of suicide-risk could be advantageous when patients are unwilling or unable to share suicidal thinking with clinicians.
Highlights
The scientific and diagnostic validity of proposed clinical disorders can be supported by biological markers [1]
Based on wavelet analysis of motility data from patients with mood disorders, we recently reported a scaling behavior of amplitudes of the rhythms at multiple time-scales ranging from minutes to hours
In the present study we investigated correlations between vulnerability index (VI), as an objective measure of multi-scale characteristics of motility rhythms, and self-assessed psychopathology including suicidal thinking operationalized as a wish to die, in human subjects monitored with actigraphic devices during an episode of major depression
Summary
The scientific and diagnostic validity of proposed clinical disorders can be supported by biological markers [1]. Development of such markers is urgent for major mood disorders, which are prevalent, often start early in life with multiple recurrences, and affect nearly 10% of the general population in a lifetime [3] They are leading international causes of disability and carry risk of premature mortality from suicide and other violence, as well as adverse outcomes of comorbid medical illnesses [3,4]. Actigraphy has documented reduced total activity or blunted amplitude of daily motility rhythms in major depression [22], often with circadian phase-advances Such alterations have been striking among subjects diagnosed with bipolar disorder during mania, depression or shortly before or after acute episodes of illness, as well as in mild or subsyndromal morbid phases [19,20,23]. A secondary aim was to test the ability of VI to distinguish between patients diagnosed clinically with bipolar versus unipolar major depression
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