06 Feb Gamma Knife Irradiation for Intractable Pain Relief
Treating severely excruciating pain by surgical/chemical hypophysectomy is not a new practice. Intractable pain, as experienced with central pain syndromes or metastatic cancer can be treated by removing or destroying the pituitary gland, but it is associated with severe adverse effects, such as panhypopituitarism, diabetes insipidus and visual dysfunction as expected. Irradiating the pituitary gland with Gamma Knife surgery (GKS) is yet another approach to destroying the gland for the purposes of pain relief with sparing much of the side effects mentioned above. Thus far, it is being reserved to be performed in patients in whom all other methods of pain relief have failed.
But how does GKS deliver the effects without the side effects? There are a number of findings that could indicate a stimulating rather than a destructive effect of GKS, such as no evidence of destructive changes on MRI or clinical or serological evidence of hormonal dysfunction, and clinical symptoms showing a stimulating effect on the hypothalamus such as rapid recovery of appetite loss and general condition. Moreover, pituitary irradiation with GKS has also been shown to be effective for patients with non-hormone related cancer and no bone metastasis.
Radiosurgical hypophysectomy (GKS) can provide significant pain relief in up to 50 percent of the patients who undergo this procedure. It involves targeting the pituitary gland with focused, high-dose radiation therapy and is performed by neurosurgeons and/or radiation oncologists. It does not require any anesthesia or implants. In preparation of this procedure, a specialized MRI is ordered to evaluate the brain anatomy and is used to pinpoint the precise area of the brain to treat with radiation. Then a very focused beam of radiation targets the pituitary gland to ablate it. The procedure itself is pain-free the patient is allowed to leave the same day. Pain relief is expected to kick in within a week.
It is important to know that radiosurgical hypophysectomy provides symptomatic relief from pain and is not curative in intent at all. But other pain indications, such as thalamic pain syndrome (central pain syndrome) have responded well to GKS. A recent study showed significant pain reduction 76.5% patients, with some reporting pain reduction within 48 hours of treatment. Furthermore, persistent pain relief for more than 1 year was observed in 38.5% of the patients. There was a reported complication of transient diabetes insipidus in one case. This suggests that GKS may be useful in thalamus-based post-stroke pain as well.
So far, the experience is still limited but accumulating quickly and is showing a high level of safety and efficacy of GKS in the majority of the patients. That makes it a very potent form of treatment for intractable severe pain that is central in origin, whether related to cancer, stroke or another indication.