extradural cortical stimulation for post-stroke aphasia

sergio canavero, neurosurgeon,
August 04, 2010

Extradural cortical stimulation (ECS) for post-stroke aphasia (PSA)

Cherney et al (1) conducted an 8 patient controlled study whose conclusion was that ECS may enhance the effect of rehabilitation for PSA. This study was conducted by implanting the stimulating paddle supplied by NorthStar Neuroscience (NSN), a company now out of business. Cherney et al. point to several weaknesses of their study, but omit to discuss several more.

1-This is not the first study of surgery for treatment of post-stroke aphasia. Two previous case reports by Canavero and Kim showed that ECS can enhance rehabilitation of PSA (see review in 2). Both targeted the premotor cortex, similarly to Cherney et al. Thus, Cherney et al. merely confirm that the premotor cortex is a valid target.

2-Cherney et al.'s study comes in the aftermath of the Everest study, the pivotal study by NSN, which employed the same kind of approach to ECS enhancement of stroke rehabilitation, i.e. same stimulating apparatus and same fMR-guided target choice and implantation. The adequately powered Everest study failed to achieve statistical significance (and led to NSN's demise), whereas smaller studies sponsored by the same company did not. Most likely, a similar study of PSA with the same technology and methods would also fail. Cherney et al.'s study is thus inconsequential in this respect.

3- Some of the major limitations of the rationale and methods employed by Cherney et al. include: 1-a fixed frequency of stimulation (50 Hz): anybody experienced in ECS knows that there is no such thing as a fixed frequency for any application (2), and both low (<50 Hz) or high (>100Hz) frequency stimulation must be assessed; 2- too short rehabilitation time (6 weeks), with other studies taking 6-12 months (2); 3- patients were only implanted on the stroke side: the contralateral side is also a viable target (2); 4- only patients displaying fMR activation of the premotor area (BA6) were implanted: fMR hot- spots may not portend successful implantation, as shown in other reports (2). Dual/triple-target stimulation, as uniquely afforded by ECS, appears indicated in many stroke cases, including the hand motor area, with its demonstrated role in language processing (see refs, in 2). Although the shape of the NSN electrode encompasses a wider area than currently used strips, nonetheless the stimulated area is still not large enough.

4- In Cherney et al.'s paper, fMR showed both post-treatment increase or decrease according to severity of aphasia, which would point to different neural processing (activation vs inhibition). Interestingly, our iomazenil-SPECT study suggested GABA changes induced by ECS even at a distance from primary targets of stimulation.

5- The strength of ECS lies in its lack of mortality or permanent morbidity, and no risk of intracranial hemorrhage or infection (unlike subdural approaches). The smooth course of the US authors' patients is to be expected.

6- ECS can be guided by preoperative TMS assessment. A flap is not necessary, as one-two burr holes are enough for any single stimulating strip, making the technique even safer (2).

In conclusion, we urge functional neurosurgeons to pursue this promising field of neuromodulation as alternative strategies for stroke rehabilitation are still imperfect.

Sergio Canavero, MD (US FMGEMS)

Turin Advanced Neuromodulation Group (TANG) Turin, Italy

sercan@inwind.it

REFERENCES

1- Cherney LR, Erickson RK, Small SL. Epidural cortical stimulation as adjunctive treatment for non-fluent aphasia: preliminary findings. JNNP 2010; 2- Canavero S. Textbook of therapeutic cortical stimulation, New York: Nova Science, 2009, pp 231-272 Canavero S, Bonicalzi V, Intonti S, Crasto S, Castellano G. Effects of bilateral extradural cortical stimulation for plegic stroke rehabilitation. Neuromodulation 2006; 9: 28-33

Conflict of Interest:

None declared

Conflict of Interest

None declared