*4.1.3 DREZotomy*

This procedure was initially performed by Sindou, in 1972, for the surgical treatment of pain. He observed that this technique also produced important hypotonia in the muscles corresponding to the severed medullary segment, and suggested its application in cases of spasticity [23, 24]. This surgery is similar to rhizotomy, but the injury here is made in the spinal cord, at the Dorsal Root Entry Zone (DREZ). The underlying mechanism in this case, is a disruption of *Ia* afferent inputs to the dorsal horn and a disruption of local circuits that contribute to muscle tone [6]. This procedure is indicated in cases of severe regional spasticity, especially those associated with pain and poor or no regional function, such as in paraplegic or hemiplegic patients with painful hyperspasticity or severe spasms [25, 26]. The surgery, which requires an intradural approach and adequate visualization of the posterior surface of the spinal cord, consists of 3-mm deep incision at the dorsolateral sulcus, down to the dorsal horn, following its axis. When spasticity is associated with focal dystonia, DREZotomy should be more deeply down to the base of the ventral horn [5]. DREZotomy can be performed at the C5-C8 medullary levels (at 35° angle) for the management of spasticity in the upper extremities or at L1-S2 levels (at 45° angle) for the lower extremity affection. The most important complications of this technique are damage to the pyramidal pathway with loss of strength and severe hypotonia, so it should be considered in patients with severe refractory spasticity who have little residual function in the limb.

### *4.1.4 Longitudinal myelotomy*

Bischof originally described the longitudinal myelotomy in 1951, and it was subsequently performed more selectively by Pourpre in 1960, and by Laitinen & Singounas in 1971 [8, 27, 28]. This procedure consists of a frontal separation between the ventral and dorsal horns at the level of the lumbosacral enlargement. The goal of surgery is to interrupt the spinal reflex arc by severing the connection between the posterior and anterior horns of the spinal cord. Through a T9-L1 laminectomy or laminoplasty, the procedure is performed at the T11-S2 medullary levels. Once the spinal cord is exposed, a posterior longitudinal sagittal incision is made deep to the central canal prior to performing a transverse cut using a stylet with a right-angled extremity, to separate the ventral and dorsal horns [7]. This surgery has been used in the treatment of patients with paraplegia, especially in cases with triple flexion and loss of sphincter function [6].
