Psychomotor Speed Flags DBS Responders With Severe Depression

Pauline Anderson

May 26, 2015

TORONTO ― Psychomotor speed may be a useful baseline predictor of patient response to subcallosal cingulate gyrus deep brain stimulation (SCG-DBS) for treatment-resistant depression, new research suggests.

Investigators at St. Michael's Hospital, in Toronto, found that patients with impaired psychomotor processing speed were less likely to respond to the treatment.

"We found that patients with psychomotor retardation, which is measured by reduced processing speed ― so a low score on the finger tap test ― were the patients who failed to respond to DBS," said study investigator Shane McInerney, MD.

Furthermore, investigators found that SCG-DBS appeared to have no adverse effects on cognition at 12-month follow-up.

The research was presented here at the American Psychiatric Association (APA) 2015 Annual Meeting.

Seriously Ill Patients

DBS involves bilateral implantation of electrodes under stereotactic guidance to a specific neuroanatomic target. One target of interest in depression is the SCG.

The new study included 20 patients with treatment-resistant depression (9 men, 11 women; mean age, 47.4 years). All patients had been in a major depressive episode (MDE) for at least 1 year, had suffered a mean of 3.9 MDEs throughout their life, and had failed at least two trials of medication. All had also failed psychotherapy, and 75% had failed electroconvulsive therapy (ECT).

Patients were receiving an average of a little more than four medications. In addition, they had a minimum score of 20 on the 17-item Hamilton Rating Scale for Depression (HAM D-17).

"You're talking about a very compromised, seriously ill population," said Dr McInerney.

Baseline neuropsychological tests assessed processing speed, using the finger tap test, which involves tapping a lever five times for 10 seconds; executive function, using the Wisconsin Card Sorting Test (WCST); attention, using the Strop Test; verbal learning and memory, using the Hopkins Verbal Learning Test (HVLT); and verbal fluency, using the Phonemic Fluency Task.

The testing showed impairment of 1 SD below the mean in executive function. Dr McInerney compared this to the typical 2 SDs below the mean found in schizophrenia patients.

"So it's not quite as stark, but if you're talking about people in the workforce, it's going to be severely impairing for them in their day-to-day work."

The patients were also 1 SD below the mean in information processing speed; other cognitive functions were within 1 SD below the mean.

The study showed that at 12 months post implant, there was a significant reduction in HAM D-17 scores, with 55% (n = 11) of patients showing response (defined as a reduction of at least 50% in HAM D-17 score). The remission rate was 20%.

In general, there was no deterioration in cognitive function at the follow-up period relative to baseline. Some cognitive deficits, for example, executive function, "normalized" during the study, said Dr McInerney.

"It's not that they had enhanced memory ― you wouldn't expect that ― but there was certainly stability of cognitive function over the course of the year after DBS."

Findings for verbal learning were "interesting," said Dr McInerney. "Verbal learning was the only cognitive measure that actually correlated with change in mood from baseline to follow-up" (P < 0.01).

"This is in line with other research," he added.

"There's evidence in the literature looking at people treated with antidepressant medication that verbal learning is often a cognitive measure that improves early on in the course of treatment, whereas things like executive function and processing speed can remain a deficit."

Although in this study, changes in cognitive function were generally not correlated with changes in mood, there was one exception. The researchers noted that responders could be distinguished from nonresponders on the basis of psychomotor speed.

Although psychomotor speed could predict response, the measure itself did not significantly improve from preintervention to postintervention, suggesting that psychomotor speed is independent of mood in terms of the response to the treatment. It also means that brain stimulation affects mood and psychomotor speed separately, said Dr McInerney.

On the basis of these findings, it is too early to start using the finger tap test as a screening tool for SCG-DBS in patients with major depression.

"This is small sample size, so I don't know if I'd go quite that far."

But it is certainly an interesting finding, he said. "It adds up in terms of the fact that psychomotor retardation is associated with lower levels of circulating dopamine in the system, and patients with that profile are often those who don't respond well to antidepressant treatment, whether it's medication or indeed DBS."

Dr McInerney reports no relevant financial relationships

American Psychiatric Association's 2015 Annual Meeting. Presented May 19, 2015.

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