Dynamics of postural control during repetitive transcranial magnetic stimulation in an adult with major depressive disorder

To the Editor

Major depressive disorder (MDD) is the second leading psychiatric contributor to years lived with a disability associated with gait or balance disorders. For instance, the postural instability, stemming from the centre-of-pressure (COP) trajectories recorded by a force platform (Figure 1(A)), is likely a moderator of positive outcomes in MDD patients following the repetitive transcranial magnetic stimulation (rTMS) treatment (Deschamps et al., 2016). Hence, we assessed the ways in which the postural control dynamics evolve during rTMS treatment in MDD patients in relation to changes in the mood states.

Figure 1.

(A) Representative illustration of centre-of-pressure (COP) trajectories recorded using a force platform in dual tasks (quiet standing balance while backward counting by two from a random number around 100), (B) evolution of mean COP velocity (mm/s) and perceived fatigue score (visual analogue scale:/10) as a function of rTMS sessions, while quietly standing on a foam surface with eyes open. Significant correlation with the linear regression line and its equation is displayed in the right upper panel, (C) forward successive correlations and (D) reverse successive correlations.

The patient had a history of recurrent MDD. She long declined further pharmacotherapy, except for lithium carbonate. Before the 4-week rTMS cure, the depression symptoms had worsened, meeting Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-V) criteria (great sadness and fatigue and concentration difficulties). The Montgomery-Asberg Depression Rating Scale (MADRS) score was 12/60.

During the first and last rTMS sessions, four postural trials in single and dual tasks were performed: stand on a firm or foam surface, with or without vision. For other sessions, only single-task trials were performed. Classic COP parameters were analysed, such as the mean velocity: higher the velocity, less-effective postural control (Deschamps et al., 2016). Before each session, the patient responded to two items assessing mood (‘I feel continuously sad’) and fatigue (‘Everything I’m doing is very demanding’) on a 10-cm visual analogue scale.

After rTMS, the MADRS scores dropped to 4 (remission, Zimmerman et al., 2004). A reduction in sadness/fatigue levels also occurred, with a drop between the first 2 weeks (mean/10: 4.1 ± 1.5 and 7.9 ± 1.7) and the last 2 weeks (2.9 ± 1.5 and 3 ± 1.8). Similarly, postural balance improved after rTMS (Figure 1(B)) (Thomas-Ollivier et al., 2016). The sadness/fatigue states and COP parameters were correlated (Table 1). The rTMS effects were observed at the third week’s end, evidenced by significant forward successive correlations starting in the fourth week. Reverse successive correlations confirmed this turning point (Figure 1(C) and (D)).

Table 1.

Correlation analyses (Pearson’s r values) (p-values) between the centre-of-pressure (COP) variables and mood states for the four postural conditions in single task.

COP measures vs sadness state (Pearson’s r)	Postural conditions
	Eyes open	Foam eyes open	Eyes closed	Foam eyes closed
Mean range_AP (mm)	0.37	0.28	0.39	0.41
Mean range_ML (mm)	0.45	0.30	0.39	0.62 (0.01)
Area (95% ellipse) (mm2)	0.2	0.28	0.57 (0.019)	0.54 (0.031)
Mean velocity (mm/s)	0.34	0.48	0.39	0.72 (0.002)
COP measures vs fatigue state (Pearson’s r)
Mean range_AP (mm)	0.04	0.54 (0.031)	0.47	0.64 (0.008)
Mean range_ML (mm)	0.13	0.58 (0.019)	0.30	0.72 (0.002)
Area (95% ellipse) (mm2)	–0.02	0.71 (0.002)	0.51 (0.044)	0.65 (0.006)
Mean velocity (mm/s)	0.08	0.67 (0.004)	0.34	0.77 (0.001)

AP: antero-posterior axis; ML: medio-lateral axis.

Significant results are indicated in bold.

*p < 0.05; **p < 0.01.

As of today, the patient is free of depressive symptoms following treatment. Furthermore, most notable improvements in posture-cognitive dual-tasking performance were observed. This likely marks a more efficient (less cognitively demanding) postural control, especially in challenging conditions. However, it remains unclear whether improvements in depressive symptoms and postural performance were due to stimulation. Interestingly, as closely linked, the balance performance and fatigue states are reliable hallmarks of depression-related psychomotor functioning. Hence, the initial fatigue and/or the postural instability may be moderators of positive patient outcomes after rTMS.