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Pain


Table 3: Treatment Outcomes After Gamma Knife Radiosurgery for Idiopathic and Multiple Sclerosis-related Trigeminal Neuralgia at the University of Pittsburgh


Outcome


Idiopathic Trigeminal MS-related Trigeminal Neuralgia


Complete pain relief (BNI score I) 40 % BNI scores I-IIIb relief


89 % Time to pain relief (median)


BNI scores I-IIIb relief at: One year


Three years Five years


Pain recurrent rate


Time to recurrence (median) Facial sensory dysfunction Anesthesia dolorosa


One month


80 % NR


46 % 38 %


48 months 11 % None


Neuralgia 62 % 97 %


10 days


83 % 74 % 54 % 38 %


75 months 5 %


None BNI = Barrow Neurological Institute; MS = multiple sclerosis; NR = not reported.


Figure 2: Flow Diagram Depicting a Suggested Approach to the Management of Medically Refractory Type 1 Trigeminal Neuralgia


Medically Refractory TN


Henson et al. compared their results with glycerol rhizotomy and GKRS.36 They observed that both procedures provided similar early pain relief rates (86 versus 92 %, respectively, for glycerol rhizotomy and GKRS), but that glycerol rhizotomy provided more rapid pain relief (<24 hours). However, glycerol rhizotomy failed significantly more frequently in the long term and was associated with more facial sensory disturbance. Percutaneous radiofrequency lesioning has similar rates of pain control (58 % pain-free after five years) but, like glycerol rhizotomy, possesses an increased risk of facial sensory dysfunction and dysesthesias.36,17 Overall, percutaneous rhizotomy approaches achieve a more rapid onset of pain relief (i.e. immediate or within days), whereas GKRS takes around a month to take effect. In addition, although GKRS appears have a lower rate of long-term pain relief versus percutaneous approaches (i.e. 29 versus 52 %, respectively, long-term pain-free rate for GKRS and radiofrequency rhizotomy),21,17


GKRS has a greatly reduced risk of facial Tolerates/wants surgery MVD Recurrent pain Cannot tolerate/refuses MVD Severe pain (i.e. cannot eat) Glycerol rhizotomy Recurrent pain Repeat rhizotomy Repeat MVD Recurrent pain Rhizotomy/GKRS Cannot tolerate/refuses MVD Severe pain (i.e. cannot eat) Glycerol rhizotomy


Cannot tolerate/ refuses rhizotomy


GKRS GKRS = gamma knife radiosurgery; MVD = microvascular decompression; TN = trigeminal neuralgia.


MVD versus GKRS have shown that MVD is superior to GKRS in achieving long-lasting pain relief.31–33


Cannot tolerate/ refuses rhizotomy


GKRS Recurrent pain Repeat GKRS


We recommend the use of percutaneous procedures in patients not medically fit for MVD and for whom pain is so severe that the latency period of GKRS is unacceptable.15


sensory dysfunction (i.e. 30 versus 54 %, respectively, for GKRS versus glycerol rhizotomy).36


The mechanism of TN in MS is felt to be related to autoimmune-mediated demyelination at points along the trigeminal system. Although there may be evidence of vascular compression on imaging or at the time of posterior fossa exploration, the results of MVD for MS-related TN have been disappointing.37,38


Percutaneous techniques have been used for


TN in MS patients for many years, but results are not as good as those in non-MS patients. As MS patients often have comorbidities that preclude open surgical intervention, GKRS is an ideal, minimally invasive approach. In our series, 97 % of patients achieved BNI score I–IIIb pain control following GKRS for MS-related TN.39


Sixty-two per cent of patients Rates of sensory dysfunction were comparable,


but patients undergoing GKRS were not exposed to any of the surgical morbidities. Another important difference lies in the rapidity with which relief takes effect. Following MVD, most patients have immediate relief (i.e. upon waking from anesthesia),4


while the median time to pain relief following GKRS is approximately one month.21


MVD has also proven more effective in achieving complete and long-lasting pain relief when compared with percutaneous lesioning techniques. Tronnier et al. retrospectively compared MVD with percutaneous radiofrequency lesioning.34


They found that with radiofrequency lesioning 152


achieved complete pain control off medications (BNI score I). BNI score I–IIIb pain control was maintained at rates of 82, 74, and 54 % after one, three, and five years, respectively. Pain recurred in 38 % of patients after a median of 75 months. Only two patients in our series developed facial sensory dysfunction (5 %) and none developed anesthesia dolorosa. These results compare favorably with our experience in treating idiopathic forms of TN (see Table 3).21 cohorts by other groups.40,41


Similar findings have been observed in small The advantage of GKRS in the setting of MS is


its exquisitely low risk of complications, even when compared with the percutaneous techniques.


GKRS also has a role in the treatment of TN from other, less common causes. For example, vascular compression of the trigeminal nerve can be caused by vertebrobasilar ectasia (VBE) in up to 2 % of cases.42 MVD in these circumstances has proven to be the most efficacious (i.e. in one series 96, 92, and 86 % pain-free rates at one, three, and 10 years after the procedure, respectively),43


but it can be technically more challenging. As a result, a high rate of surgical complications has been US NEUROLOGY


there was a 50 % risk of pain recurrence after two years, whereas 64 % of patients undergoing MVD were still pain-free after 20 years. A meta-analysis of 28 studies confirmed that MVD was superior to radiofrequency lesioning.35


Taken together with the accepted vascular


compression mechanism of TN, these results suggest that, for patients who are surgically fit and willing to accept the risks of surgery, MVD is the best approach to achieve long-lasting pain relief.


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