Objective: In the current study we explored the response inhibition paradigm through Stop Signal Reaction Time (SSRT) task in patients with lithium induced tremor.

Background: Lithium is a standard treatment for patients with bipolar disorder and is well known to cause tremors. Understanding the deficit in motor functions in lithium-induced tremor may shed light on the pathophysiology of this disorder. Previous studies suggest that patients with movement disorders have impaired response inhibition. The stop-signal reaction time (SSRT) is a way to quantify motor-response inhibition based on a ‘Horse Race Model’ proposed by Logan and Cowan,1984. We have further modified this using a Bayesian statistical approach for more reproducibility, termed the optimal combination SSRT (ocSSRT).  In this study, we have measured oc-SSRT in lithium induced tremor patients.

Method: Patients with bipolar disorder in an euthymic state were recruited from the psychiatry OPD, diagnosed as per DSM-V criteria. The depressive and manic states were quantified using the Becks Depression Inventory (BDI II) and Young Mania Rating Scale (YMRS) scales. The estimation of SSRT was performed through a Go/No-Go task. A portable battery-operated box programmed to execute and analyse the task was used. The participants were asked to release the button seeing the illumination of the GO (green) LED as fast as possible and abort the ongoing movement when the GO signal was followed by a STOP (red) signal.  The lithium levels in the blood were obtained from the Therapeutic drug monitoring (TDM) reports.

Results: We have recruited 27 lithium induced tremor patients and 31 age matched healthy controls. The mean age of the patients and healthy controls were 33 and 34 years respectively. The mean BDI II and YMRS scores were 16.6 ± 9, 8.4± 7. We found a significant difference in oc-SSRT (337±87, 261± 85 p= 0.002) and Med RT (583± 96, 463±83 p<0.001) between the groups. We found a positive correlation with oc-SSRT and blood lithium concentration (rho= 0.659, p=0.020).

Conclusion: These preliminary results indicate that the response inhibition paradigm is impaired in the patients with lithium induced tremor and it correlated with lithium concentration.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/response-inhibition-in-patients-with-lithium-induced-tremor/