Understanding autonomic changes in bipolar disorder: Sympathetic skin response from the manic phase to euthymia

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Background: Autonomic dysfunction, characterized by heightened sympathetic and diminished parasympathetic activity, is increasingly recognized as a significant factor in the pathophysiology and therapeutic management of bipolar disorder (BD). The aim of this study is to investigate the changes in sympathetic skin response (SSR) among BD type 1 patients during the manic phase compared to their state after clinical remission. Methods: This retrospective cross-sectional study enrolled 17 patients who were newly diagnosed with BD type 1 in the manic phase, adhering to DSM V criteria, over 4 years from January 2018 to December 2022. All subjects received treatment with sodium valproate, and SSR testing was performed during both the manic phase and following a washout period. The latency and amplitude of bilateral palmar and plantar SSRs were examined using electrical stimulation of the median and tibial nerves. Statistical analyses were conducted using paired T-tests and Mann–Whitney U tests to assess the mean differences in SSR latency and amplitude pre- and post-treatment. Results: The treatment led to a statistically significant reduction in SSR latency for the right tibial nerve (from 2.380 ± 0.370 to 2.126 ± 0.241 seconds, p = 0.014) and the left median nerve (from 1.829 ± 0.410 to 1.600 ± 0.217 seconds, p = 0.033), indicating moderate effect sizes. In contrast, SSR amplitude demonstrated minimal variation across all examined nerves, with no statistically significant increase observed following treatment (all p-values = 0.05). Limitations: The small number of participants in the study could affect the reliability of the results. Conclusion: The results of the study indicate that SSR latency may serve as a promising biomarker for evaluating autonomic function in patients experiencing manic and euthymic phases of BD following mood stabilizer treatment. Nonetheless, further validation through larger cohort studies with long-term follow-up is essential to corroborate these preliminary findings and better understand the implications for clinical practice.