The dorsal root ganglion (DRG) contains the cell bodies of first-order sensory neurons, each of which project an axon from a peripheral receptor, and centrally to the posterior horn of the spinal cord, where they synapse with second-order neurons.
There is one DRG for each spinal nerve root supplying the posterior aspect of the head, the trunk and the extremities; in the face, this function is carried out by the trigeminal ganglion.
Unless prevented or treated, injury to the DRG often leads to the development of a chronic neuropathic pain state. Injection procedures that target the DRG could be used in the treatment of any radicular pain syndrome, such as primary radicular irritation, postherpetic neuralgia.
Neuropathic pain resulting from injury to the DRG neurons, by infection, mechanical trauma, or inflammation resulting in the development of persistent low-threshold spontaneous firing of the neurons.
The C2 nerve root is implicated in the production of occipital neuralgia, which may be more properly referred to as a C2 radicular pain syndrome. Block at the DRG, particularly with cold-pulsed RF, may be an effective treatment.
Similarly, at all spinal levels neuropathic radicular pain may be diagnosed by selective local anesthetic blockade of the relevant nerve root, and potentially modulated by application of cold-pulsed RF energy.
ISSUES COMMON TO DRG BLOCKS AT ALL LEVELS
RF blockade of the DRG carries the same risks as any procedure that accesses the neural foramen.
These include inadvertent injury to nerves (the spinal root, DRG, and the spinal cord at relevant levels), vascular injury (to the spinal arteries at thoracic and lumbar levels, and the vertebral arteries at cervical levels).
Infection, and hematoma.
At cervical and thoracic levels, there is the additional risk of pneumothorax.
Neurolytic techniques directed at the DRG, including thermal radiofrequency and chemical lysis, carry a greater risk of producing deafferentation pain, and are hard to control. Pulsed dose (low-temperature) radiofrequency treatment of the DRG is a much safer technique.
Contraindications to Injection
Preoperative consultation with the patient including history, a review of diagnostic studies, and physical examination is the standard of care.
Physical examination should include heart, lungs, and airway; the proposed injection site; as well as a relevant neurologic and spinal examination.
Review of medications should pay particular attention to anticoagulants, which should be discontinued with sufficient time to allow for normalization of clotting.
Review of the history of allergic reactions, with particular attention to iodinated contrast sensitivity. Use of contrast is critical to placement of the needle adjacent to the DRG, and in patients with a contrast allergy pretreatment will be necessary to reduce this risk.
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