The dorsal root entry zone (DREZ) is a small, specialized region within the spinal cord. It functions as a gateway for all the body’s sensory information to enter the central nervous system. Its integrity is fundamental for the nervous system to correctly interpret inputs from the environment.
What is the Dorsal Root Entry Zone?
The dorsal root entry zone is located at the lateral aspect of the spinal cord, where sensory nerve fibers, known as dorsal roots, converge and penetrate the spinal cord. This anatomical structure consists of nerve fibers, glial cells, and blood vessels. It is where different types of sensory information, such as touch, temperature, and pain, are organized and undergo initial processing.
The dorsal roots are bundles of nerve fibers that arise from dorsal root ganglia, which house the cell bodies of primary sensory neurons. These fibers enter the spinal cord via multiple small rootlets. The DREZ encompasses the central portion of these dorsal rootlets, the medial part of the tract of Lissauer, and layers I to V of the dorsal horn, where the afferent fibers terminate and synapse.
Its Role in Pain Pathways
The dorsal root entry zone processes and modulates pain signals. Pain signals travel along peripheral nerves to the dorsal root ganglia and then enter the spinal cord through the dorsal roots, arriving at this zone. Within the DREZ, particularly in the superficial layers of the dorsal horn (laminae I and II), these pain-transmitting fibers synapse with other neurons.
This area involves a balance of excitatory and inhibitory neurons that can either intensify or diminish pain perception. For instance, large myelinated fibers, which transmit non-painful touch and vibration, can stimulate inhibitory neurons within the dorsal horn, releasing neurotransmitters like GABA to suppress pain signals. This mechanism is part of the gate control theory of pain.
Conditions Linked to Dorsal Root Entry Zone Dysfunction
When the dorsal root entry zone does not function correctly, various neurological conditions and symptoms can arise, particularly those involving chronic pain. Damage or abnormal activity in this zone contributes to various neuropathic pain conditions. These include phantom limb pain, where individuals experience pain in an amputated limb, and post-herpetic neuralgia, a persistent painful complication of shingles.
Brachial plexus avulsion injuries, where nerves are torn from the spinal cord, frequently cause severe neuropathic pain due to DREZ damage. This damage can lead to disorganized and uncontrolled firing of nerve cells within the DREZ, similar to electrical impulses seen in a seizure, which the brain interprets as pain. Spinal cord injuries can also induce neuronal hyperexcitability in DREZs both above and below the injury level, leading to persistent below-level neuropathic pain described as sharp, burning, electrical, or stabbing.
Targeting the Dorsal Root Entry Zone for Treatment
Interventions can target the dorsal root entry zone to alleviate severe, intractable pain unresponsive to other treatments. Dorsal Root Entry Zone Lesioning (DREZotomy or DREZ lesioning) is a neurosurgical technique that creates small lesions in this area to interrupt abnormal pain signals. The procedure aims to selectively destroy nociceptive fibers within the lateral bundle of the dorsal rootlet and the superficial layers of the dorsal horn gray matter, while preserving inhibitory fibers.
DREZ lesioning is considered for severe neuropathic pain conditions such as brachial plexus avulsion injuries, post-traumatic neuropathic pain, spinal cord injury pain, or cancer-related pain. During the procedure, a neurosurgeon accesses the spinal cord, often through a laminectomy, and uses radiofrequency energy, laser, ultrasound, or microsurgical techniques to create precise lesions within the DREZ. This process aims to silence overactive nerve cells and block pain messages from reaching the brain.