Surgical control of the human thalamocortical dysrhythmia:

Abstract

Reactualization of the medial thalamotomy, performed since the fifties in cases of neurogenic pain, has been guided by the discovery of low threshold calcium spike bursts at frequencies in the delta–theta range in the posterior part of the central lateral (CL) nucleus. This thalamic rhythmicity is transmitted to the cortex through thalamocortical resonant properties, giving rise to the thalamocortical dysrhythmia, proposed to be the mechanism of neurogenic pain as well as other central nervous system (CNS) dysfunctions. Magnetic resonance- and microelectrode-guided stereotactic CL thalamotomy was implemented in 96 patients suffering from chronic therapy-resistant peripheral or central neurogenic pain (mean age: 56±15 years; pain duration before surgery: 7.5±8 years). At a mean follow-up of 3 years, 9 months±2 years, 9 months, 53% of the patients benefited from a relief superior to 50% (complete relief in 18.7%). Further analysis of the results demonstrated a significant difference between patients suffering from intermittent as compared with continuous pain. Patients with continuous pain showed only a mean relief of 20.4±25.8% in contrast to the 66±39.2% obtained for patients with intermittent (episodic or paroxysmal) pain manifestations. This was confirmed by the pre- and postoperative visual analogue scale scores showing a significant decrease (59.2%) only in the patient group with intermittent pain. Allodynia was suppressed in 57.3% of the patients. Parameters such as the preoperative pain duration or the site of the causal lesion did not affect the surgical outcome. In 28 patients suffering from unilateral continuous pain, the addition of an ipsilateral CL thalamotomy provided a further significant pain relief. A suppression of drug intake was observed in 31.6% of the patients. Complications occurred in 11.5% of the patients and led to a long term significant disability in only one case. In conclusion, CL thalamotomy is a safe neurosurgical option for neurogenic pain, especially for patients suffering from intermittent pain or allodynia. Its limitation in cases of continuous pain indicates the necessity to explore other stereotactic targets outside of the medial thalamus.