Manual dexterity impaired more in bipolar disorder than unipolar depression
MedWire News: Manual dexterity is more severely impaired in patients with bipolar disorder than in those with unipolar major depression, researchers report.
They found that bipolar patients had greater impairment of gross manual motor dexterity despite having similar severity of depressive symptoms to unipolar depression patients, irrespective of handgrip strength and use of antipsychotic and lithium medications.
This difference in movement dexterity may reflect differing pathologies that could be used to distinguish the two depressive disorders.
Daimei Sasayama (Shinshu University School of Medicine, Matsumoto, Japan) and colleagues used the Purdue pegboard test to assess manual dexterity in 98 patients with unipolar major depression, 48 euthymic or depressed patients with bipolar disorder, and 158 age- and gender-matched healthy control individuals.
The pegboard test comprises two vertical arrays of 25 holes in which pegs are placed one hand at a time, and then with both hands simultaneously, under timed conditions (30 seconds each trial), the researchers explain. Scores are based on how many pegs were placed within the time limit, with the sum of the right, left, and both hands subtest scores (R+L+B) used to represent gross dexterity of the fingers, hands, and arms.
The team reports in the Journal of Affective Disorders that R+L+B scores were significantly lower in the bipolar disorder and unipolar depression patients than in the control individuals, and in the bipolar depression patients than in the unipolar depression patients. There was no difference among groups in results of a handgrip force test.
Depression severity did not correlate with any subtest scores, whereas antipsychotic use correlated negatively with R+L+B scores in both patient groups, and with lithium dose in the bipolar group.
However, the difference in R+L+B scores between unipolar depression and bipolar disorder remained statistically significant after controlling for age, gender, lithium dose, and chlorpromazine-equivalent dose.
"The functional difference strongly suggests different pathological conditions," comment Sasayama et al.
They note that previous research has shown that the relationship between psychomotor impairment and catecholamine function may be stronger in bipolar depression than in unipolar depression, so the impairment of dexterity "may be etiologically different" in the two conditions.
Also, they speculate that some of the unipolar depression patients exhibiting impaired motor dexterity in this study may go on to experience a manic/hypomanic episode and be rediagnosed with bipolar disorder. Alternatively, unipolar depression may lie on a continuum of bipolar disorder whereby patients have only slight impairment of dexterity relative to healthy individuals, they say.
"Future studies should assess the motor dexterity in bipolar spectrum conditions to examine these possibilities," the researchers write.
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By Caroline Price