Role of Pituitary Radiosurgery for Management of Intractable Pain and Potential for Future Work

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Rationale: Up until two or three decades ago, cancer pain had been treated with surgical/chemical hypophysectomy, and there was a report that central pain (thalamic pain syndrome) had also been tried to be controlled with chemical hypophysectomy. The clinical results showed that hypophysectomy provided most of the patients relief from severe pain. However, severe accompanying adverse effects (panhypopituitarism, diabetes insipidus, and visual dysfunction) were found in almost all patients. This historical evidence prompted us to perform gamma knife surgery (GKS) for control of this kind of severe intractable pain with a high irradiation dose to the pituitary stalk/gland as an alternative hypophysectomy. This method has provided the majority of patients relief from severe pain, and surprisingly without any of the above-mentioned complications. Material and Methods: We have been carrying out a prospective collaborative study in Prague, Hong Kong, and our institute (Tokyo) for this treatment to evaluate the efficacy and safety of this method. Indications for this treatment are: (1) no other effective treatment prior to GKS; (2) general condition is considered good (KPS > 40%); (3) morphine is effective for pain control (for cancer pain), and (4) no previous treatment with radiation (GKS/conventional radiotherapy) for brain metastasis. In our institutional experience, in Tokyo, we have treated 10 patients who suffered from severe cancer pain due to bone metastasis with GKS, and 15 patients who suffered from post-stroke thalamic pain syndrome. The target was just the border in between the pituitary stalk and gland. Maximum dose was 160 Gy for cancer pain and 140 Gy for central pain. We could follow up all patients (>1 month) with cancer pain and 8 patients (>6months) with thalamic pain syndrome. Results: All patients (10/10) with cancer pain experienced significant pain reduction, and 87.5% (7/8) of the cases with thalamic pain syndrome initially experienced significant pain reduction. Some of patients felt reduced pain within several hours. Pain reduction was apparent within 7 days (median 2 days). No recurrence was observed in the patients with cancer pain; on the other hand, real recurrence was seen in 71.4% (5/7) of the cases with thalamic pain syndrome over 6 months of follow-up. No other complication has been observed in any of the cases up to now. Conclusions: Our clinical study protocol is not mandatory and still insufficient. In particular, much more investigation for clinical results of GKS in patients with thalamic pain syndrome is needed to optimize this treatment protocol. However, efficacy and safety have been shown in all of our cases. We believe that this treatment has a potential to control severe pain well, and that GKS plays a very important role in the field of intractable pain management.