Chin Med J (Taipei) 1998;61:S29.

When All Else Fail, What Can You Do?----Spinal Cord Stimulation

Wei-Zen Sun, M.D., PhD.

Division of Pain Management, Department of Anesthesiology, National Taiwan University Hospital, Taipei, Taiwan

Abstract

It is well accepted that the neuropathic pain, a state of intense spontaneous pain associated with impairment in sensory function, is mainly caused by neuronal sensitization in different levels of the central nervous system. By definition, the state of central sensitization is manistated as an expanded receptive field, behavioral hyperalgesia, and reduced threshold for mechanical stimulation. Although numerous studies in animal have demonstrated the pivotal role of excitatory amino acids (EAA), e.g., glutamate and aspartate, pharmacological approaches towards neuropathic pain remains largely unsettled. A critical limitation for various NMDA antagonists, e.g., ketamine and dextromethorphan, is the development of profound psychotropic effect before any therapeutic serum level is achieved. While topical application of capsaicin can be the drug of choice specifically targeting at the small unmyelinated fibers, clinical evidence fails to prove any such response unless very high dose is given. While opioid analgesic agents and tricyclic antidepressants are the most commonly used drugs for moderate to severe pain, the dose-response range and relationship is clearly different from those of the other chronic pain patients. It is suggested that neuropathic pain is categorized as "opioid unresponsive". Consequently, neuropathic pain remains the most difficult symptom for effective treatment. On the other hand, functional augmentation by spinal cord stimulation is now the standard of choice when all drug treatments fail.

In the past two decades, spinal cord stimulation has been extensively used in treating neuropathic pain with distinct results. In early 1980's, longterm success rate for failed back syndrome is less than 30% in North America. The response has greatly improved in 1990's by care patient selection, the use of 4 to 8 lead catheter, and percutaneous implantation technique. Current practice for spinal cord stimulation consists of two-stage procedure: the first stage is to put an temporary lead for trial while the second stage is to implant the catheter and power supply on a permanent basis. The approach of trial stage allows for more stringent evaluation of patient selection, position of lead, mode of stimulation and treatment efficacy. Thus, patient with inappropriate underlying problems, e.g., drug abuse tendency, psychiatric disorders, can be removed from the candidate for the implantation. Despite the expense and risk for machinery dysfunction, the distinct benefits with reversible capability and least invasiveness, unlike most neurosurgical procedures, have made spinal cord stimulation the best choice for the majority of patients and clinicians in United States.

In summary, it is now recommended that spinal cord stimulation is a reversible approach towards neuropathic pain when standard medications fail. However, to enhance its efficacy and to reduce the failure rate, it is essential that the implantation be performed in a non-invasive manner and two-stage procedure.

[Chin Med J (Taipei) 1998;61:S29.]