Peripheral Nerve Stimulation
Peripheral nerve stimulation (PNS) is a neuromodulation technique in which electrical current is applied to the peripheral nerves to ameliorate chronic pain. First described in 1967, a variety of techniques have since been developed, and applied to many different pain problems.
Generally speaking, PNS is indicated for the treatment of chronic pain, localized to a peripheral nerve distribution, that is not amenable to less invasive measures. PNS is extremely useful for treating pain in a distribution that is not accessible by spinal cord or spinal nerve root stimulation. Examples include trigeminal branch stimulation, occipital nerve stimulation, and subcutaneous peripheral nerve stimulation. Trigeminal neuropathic pain, occipital neuralgia, supraorbital neuralgia are common disorders treated with cranial PNS. Tibial neuralgia and inguinal neuralgia are extremity and trunk peripheral nerve disorders amenable to treatment with PNS. Cranial peripheral nerve stimulation is also currently being investigated for the treatment of a variety of headache disorders, including migraines, hemicrania continua, SUNCT, and cluster headache.
The overall strategy is similar to other forms of neurostimulation. Patients routinely undergo a psychological screening to rule out psychological amplifiers of pain, such as depression, substance abuse, behavioral problems, etc. Some practitioners advocate the use of local anesthetic injections along the peripheral nerve as a screening tool to select those patients who are most appropriate for PNS. The effectiveness of this as a screening tool has not been entirely elucidated.
A trial period with temporary electrodes generally lasts about a week. If sufficient pain relief occurs, then a permanent system is implanted. Both percutaneous as well as paddle leads are commonly used, depending upon physician preference. Paddle leads seem to be less prone to migration, as for spinal cord stimulation. This may be fairly important, as PNS electrodes may be located in areas of excessive movement and stress, such as across multiple joint surfaces.
For superficial peripheral nerves, such as the trigeminal and occipital nerves, individual leads are placed just under the skin, overlying the nerves. Fluoroscopic guidance may be helpful in some cases. Intraoperative testing confirms that stimulation paresthesias are in the appropriate location.
For larger peripheral nerves, which are often deeper, and adjacent to important neurovascular structures, an open approach is generally used. This lessens the risk of injuring these structures using a blind, percutaneous approach. The target nerve is subjected to an external neurolysis, and the desired lead(s) is(are) placed in the vicinity of the nerve. When a paddle lead is used, a small layer of fascia is sandwiched between the nerve and the electrode array to lessen painful levels of direct stimulation. Intraoperative testing confirms appropriate coverage. Permanent leas are connected to an implantable pulse generator. The thigh and upper arm are fairly accessible sites for extremity stimulators, whereas the subclavicular, subcostal, and buttock regions are reasonable sites for cranial nerve electrodes.
Subcutaneous Peripheral Nerve Stimulation
Subcutaneous peripheral nerve stimulation (SPNS) is a variant of PNS in which the electrodes are placed in the subcutaneous space directly subjacent to the region of pain. The electrodes stimulate the small, unnamed cutaneous peripheral nerves, and not larger, named peripheral nerves. Thus, areas of pain not confined to a specific peripheral nerve distribution may be targeted. This type of stimulation may be quite useful to treat pain located in areas that may not be targeted with more conventional forms of stimulation, such as spinal cord stimulation, spinal nerve root stimulation, or PNS. Postherniorrhaphy pain, low back pain, and axial neck pain are examples of emerging indications for SPNS.
High-quality, published studies reporting the results of peripheral nerve stimulation are rare, as they are for other types of neurostimulation. But in general, peripheral nerve stimulation has comparable success rates to other forms of stimulation in the treatment of chronic pain.
Adapted: http://wiki.cns.org/wiki/index.php/Peripheral_Nerve_Stimulation, July 25th, 2010