Dorsal root ganglia (DRG), which contain the cell bodies of primary afferent neurons transmitting sensory information from the periphery to the central nervous system, play a key role in the pathogenesis of chronic pain syndromes caused by spinal pathology and peripheral nerve injury. The evidence supporting a primary role for the DRG in chronic pain states has led to the growing use of treatment directed at dorsal root ganglion.
Dorsal root ganglion blocks can provide pain relief in patients experiencing nerve pain in the upper or lower limbs and in the thoracic area. Dorsal root ganglion blocks can also provide important diagnostic information, following which pulsed radiofrequency treatment can be used for sustained pain relief in some patients. However it is important to note that in some cases injection treatment may not provide the desired results or the pain relief may not be sustained.
Information Sheet
Dorsal root ganglia are large collections of neurons on the dorsal spinal roots. Ganglia are usually located in the intervertebral foramina, immediately lateral to the perforation of the dura mater by the roots. The first and second cervical ganglia lie on the vertebral arches of the atlas and axis, respectively. The sacral ganglia lie inside the vertebral canal, and the coccygeal ganglion usually lies within the dura mater.
Following peripheral nerve injury, ion channel modulation occurs leading to nociceptor sensitization, expansion of receptive fields, diminished central inhibition, increased neuronal excitability in the spinal cord and reorganization in the dorsal horn. Ion channel alterations that are in part responsible for these effects include proliferation of voltage-dependent sodium channels in the DRG, down regulation of voltage-gated potassium channels and increased expression of the calcium channel alpha-2 delta-1 subunit.
A growing body of literature supports a relationship between peripheral nerve injury and sympathetic sprouting in the DRG. Hyperexcitability and ectopic firing occur not only at the site of injury, but also in DRG cell bodies The end result of these changes is peripheral and central sensitization, manifesting as spontaneous pain, hyperalgesia, and allodynia.
The procedure is usually done on an outpatient basis. The procedure is performed under fluoroscopic guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that they may need repeated injections.
Although serious complications are rare with DRG procedures, they are not risk-free. There are multiple potential complications associated with transforaminal epidural injections, including intravascular injection, vascular trauma, air and particulate embolism, cerebral thrombosis, epidural hematoma, infection, postdural puncture headaches, neural and/or spinal cord damage.
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