Pallidothalamic Tractotomy (Forel's Field H1-tomy) for Dystonia: Preliminary Results

The pallidothalamic tract connects the globus pallidus internus with the ventroanterior and ventrolateral parts of the thalamus. Lesioning or stimulation of the pallidothalamic tract has ameliorating effects on dyskinesia and dystonia in patients with Parkinson disease. However, the effect of the procedure on dystonia due to other etiologies has not been reported.

We retrospectively analyzed patients with dystonia who underwent unilateral pallidothalamic tractotomy between July 2017 and October 2018 at Tokyo Women's Medical University Hospital. The Burke-Fahn-Marsden Dystonia Rating Scale-Movement Scale was used to evaluate the severity of dystonia at three time points (before surgery, 3 months postoperatively, and the last available follow-up). Adverse events were also evaluated.

Eleven patients underwent unilateral pallidothalamic tractotomy, including 5 with generalized dystonia, 4 with segmental dystonia, and 2 with focal (cervical) dystonia. All patients had undergone unilateral pallidotomy before contralateral pallidothalamic tractotomy. The mean interval between the previous surgery (pallidotomy) and pallidothalamic tractotomy was 9.5 ± 3.1 months. The mean follow-up period was 11.5 ± 4.2 months. The Burke-Fahn-Marsden Dystonia Rating Scale-Movement Scale scores at 3 months after pallidothalamic tractotomy (5.8 ± 8.4) and at the last available follow-up (5.6 ± 8.3, P < 0.001) were significantly improved compared with that before pallidothalamic tractotomy (21.8 ± 16.3). The most common adverse event was reduced voice volume (6 patients), which was mild and did not interfere with the patient's daily activities.

This study suggests that pallidothalamic tractotomy can be an alternative treatment target for dystonia. A larger and longer prospective study is needed to elucidate the safety and efficacy of pallidothalamic tractotomy for dystonia.