Introduction: Positive dose-response relationship with the use of Transcranial direct current stimulation (tDCS) in post-stroke upper limb motor recovery demands investigating the efficacy of higher tDCS doses. Safety and tolerability of tDCS current higher than typically used 2 mA has not been investigated in stroke patients.
Hypothesis: tDCS application up to 4 mA for 30 minutes is safe and tolerable in stroke patients
Methods: A 3+3 study design with current escalation schedule of 1, 2, 2.5, 3, 3.5 and 4 mA was adopted for this tDCS safety study (Fig. A). Patients with first-ever ischemic stroke and unilateral hemiparesis were recruited. Single session of tDCS and customatory occupational therapy for 30 minutes using a device (Chattanooga Ionto) with 5х7 cm2 sponge electrodes (Soterix Medical) on a bihemispheric montage (C3/C4, anode on lesional side) were administered. Stopping rules were (1) second degree scalp burn, or (2) seizure, or (3) new lesion(s) on DWI sequence of MRI or decreased ADC. Tolerability was assessed by tDCS questionnaire administered before and after tDCS. Body resistance and skin temperature at electrode contact site were monitored in real time.
Results: Eighteen patients were enrolled and completed the study. The current was escalated to 4 mA without any major safety concerns (stopping rule). 50% of patients revealed transient skin redness at anodal site and 17% at cathodal side. No patient had any persistent skin perception issues at the end of tDCS (Fig. B). We also present real-time monitoring of body resistance and skin temperature to ensure safety during tDCS administration (Fig. C). Skin barrier remained intact through tDCS, as demonstrated by absence of abrupt decrease in body resistance (<400 Ω). Skin temperatures remained well below body temperature (range 26°C-35°C)
Conclusion: Our data support that tDCS current up to 4 mA is safe and tolerable in ischemic stroke patients. Efficacy and safety should be further tested in a phase II study.