髄内病変による中枢性疼痛に対する脊髄硬膜外刺激

Spinal Epidural Stimulation for Central Pain Caused by Spinal Cord Lesion

I．はじめに

　Deafferentation painとは末梢の侵害受容器の関与による痛みではなく，痛覚求心系の障害の結果出現する痛みを言う．求心路の末梢で遮断される場合（末梢神経の障害）と中枢で遮断（二次ニューロン，三次ニューロンの障害）される場合に大別される．その明確な発生機序は未だに不明である^7）．

　しかし，臨床的には，deafferentation painに対し慢性的電気刺激療法が，一部の患者で有効であることが知られている．この中で，脊髄硬膜外刺激（DCS；dorsalcolumn stimulation）は，1970年Shealy^22）らが，臨床応用として，慢性疼痛の患者に行って，良好な結果を得て以来，様々な種類の慢性疼痛を有する患者に行われてきている．DCSは，一般的に中枢性のdeafferentationpainには効果が乏しいといわれているが，この中には効果が得られたという報告も散見される^{8,18,21,26,28）}．

　今回，われわれは脊髄髄内に病変を有する頑痛症例に対し脊髄硬膜外電気刺激治療を行った．ここでは，その治療効果を原因疾患，痛みの発生部位，電極設置部位，刺激条件，痛みの性質，有痛期間，試験刺激時のpares-thesia（electrical paresthesia），刺激時および刺激を切った後の効果，初期効果（刺激電極設置後1週間の効果；initial pain relief），初期効果にわけて検討し，DCSの除痛効果を左右する因fを考察し，あわせて，これまでの文献上の報告例と比較検討した．また，deafferenta-tion painの発生機序や，脊髄硬膜外刺激による除痛機序についても，若干の考察を加えた．

Epidural spinal cord stimulation was carried out in 4 patients with denervation caused by spinal cord lesion, and we reviewed previously reported cases.

Initial result showed at 1 week in 100% of our cases, but about 1/3 of the cases, even those with the same denervation caused by spinal cord lesion, had no pain relief at this stage in previously reported cases. In our cases, excellent pain relief was gained temporarily, even though the painful area and the spinal cord lesion were separated somatotopically in 2 cases (case 3, 4). Tem-porary success bore no relationship to quality and dura-tion of pain.In all cases except case 1, a rapidly de-creasing effectiveness was noted, and finally no pain re-lief was gained at all after 4, 3 and 5 months, respec-tively. In case 1 there was persistent pain relief esti-mated at 70-80% after 19 months, only when the spin-al cord was stimulated. Epidural stimulation also pro-duced sensations in the painful area.

Spinal cord stimulation would suppress at least the dorsal horn neurons which were destroyed by various kinds of diseases.

A decline in effectiveness with time would occur due to essential causes of the deafferentation pain, such as anatomical and regeneration factors.