Prefrontal tDCS improved cognition after stroke, in 74 patients

Design

Randomised, double-blind, sham-controlled trial with a resting-state functional MRI subgroup

Population

74 patients with post-stroke cognitive impairment; 38 active dual tDCS, 36 sham, all receiving conventional therapy

Primary outcome

Montreal Cognitive Assessment after 20 daily sessions of 2.0 mA stimulation over bilateral dorsolateral prefrontal cortex

Effect

MoCA improvement 5.74 (SD 2.76) vs 2.69 (2.69), t=4.799, p<0.001, with gains concentrated in attention and memory

Post-stroke cognitive impairment has no established pharmacological treatment and rehabilitation effects are modest. This randomised, double-blind, sham-controlled trial gave 74 patients conventional therapy plus either active dual transcranial direct current stimulation over the dorsolateral prefrontal cortex - anodal left, cathodal right, 2.0 mA for 20 minutes daily over 20 sessions - or sham.

Montreal Cognitive Assessment scores improved by 5.74 points (SD 2.76) with active stimulation against 2.69 (2.69) with sham (t=4.799, p<0.001), with the difference concentrated in attention and memory. A 36-patient imaging subgroup showed increased regional homogeneity in the right middle temporal and left inferior frontal gyri, reduced connectivity in two pairs, and increased small-worldness and global efficiency, with the imaging changes correlating with clinical improvement. Adverse events were rare and self-limiting.

A three-point difference on the Montreal Cognitive Assessment is clinically meaningful if it is real, and this is a properly sham-controlled, double-blind design, which is more than much of the stimulation literature offers. The reservations are size and duration: 74 patients at one centre, no follow-up beyond the treatment period reported, and no functional outcome beyond the Barthel Index. The imaging findings are supportive rather than confirmatory - a 36-patient functional MRI subgroup with multiple regions tested will produce some correlations.

So this is a reason to take tDCS seriously in post-stroke cognitive impairment and not yet a reason to buy a device. Twenty daily sessions is a substantial commitment for a patient in rehabilitation, and whether the gain persists after the sessions stop is the question that decides whether it is worth it.

• Do not commission transcranial stimulation for post-stroke cognition on a single 74-patient trial
• Note the burden: 20 daily sessions, which competes with time in conventional rehabilitation
• Durability after the stimulation course is unreported and is the deciding question
• Screen for and treat depression, delirium and sleep disorder first - they are commoner causes of poor cognition after stroke
• Read the imaging findings as mechanistic support, not as independent evidence of benefit

The statistics, in plain English

Both groups improved - sham gained 2.69 points - which is why a sham-controlled design was essential: much of the recovery here is spontaneous and would have been credited to the device in an uncontrolled study. The 3-point between-group difference exceeds what is usually considered meaningful on a 30-point scale, and p<0.001 makes chance unlikely in this sample. What a single-centre trial of 74 cannot tell you is whether the effect replicates elsewhere or lasts, and the functional MRI subgroup of 36 tested many regions, so those correlations are exploratory.

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