Familial primary amyloidosisの腓腹神経の微細構造

ULTRASTRUCTURAL STUDY OF SURAL NERVES IN FAMILIAL PRIMARY AMYLOIDOSIS

はじめに

　Familial primary amyloidosisは腎，肝，脾など一般臓器に，さらに皮膚，末梢神経などに，小血管を中心としてamyloidの沈着する疾患である。末梢神経症状を示す本疾患の型には，ポルトガル型と北米型があるが，ここに述べる症例は前者の範疇に属するものである。

　本症の臨床上の特徴として四肢の温度・痛覚の著明に侵されたほぼ完全な解離性感覚障害が挙げられる^1,9）。電気生理学的検査では末梢神経伝導速度の低下は主要所見でなく，in vitroでの生検神経興奮伝導検査ではCpo—tentialの消失ないし著明な低下，A　δ　potentialのかなり明らかな消失とA　α　potentialの中等度の低下が述べられている^9）。末梢神経病変としては，血管周辺ないし内鞘へのamyloidの沈着であり，この意味では間質性neuropathyとみなすことができる。しかしながら，これに加えて軸索の障害（断裂，狭小化など），脊髄神経細胞の高度の変性所見などがあり，実質障害が強いことが述べられている^{1,7-9,13,14,17）}。

The biopsied sural nerves of two cases of familial primary amyloidosis were studied using the light and electron microscope. Each of two cases was a member of the defined family; one came from the family previously reported by us and another was failed to confirm the relation to the former family, although both lived in the same city. The light microscopic observations disclosed the depositsof amyloid around the blood vessels in the en-doneurium and marked loss of myelinated fibers. In many occasions the amyloid mass was also seen freely from the vessels and was hardly considered to have a contact to the vessels. Ultrastructurally, amyloid mass was composed of fine amyloid fibrils of about 100 A in diameter. These fibrils extended among the Schwann cell cluster, fibroblasts and collagen fibrils without a limiting membrane. However, in the very occasion, amyloid fibrils were attached to the basement membrane of endothelial epithelium and of smooth muscle cells and were seen together with the collagen fibrils. The cy-toplasmic reactions suggesting either of amyloid fibril formation or of phagocytosis of the fibrils were not observed in any kind of endoneurial cells. Most Schwann cell clusters were composed of many irregularly shaped and flat, or sometimes round or oval Schwann cell processes which have many filaments in their cytoplasm. Many of these clusters lacked the axis cylinders and were con-sidered to be denervated Schwann cell clusters. These two or several clusters usually made a contact with each other and formed a group of clusters. In addition, some Schwann cells showed markedly proliferated granulated endoplasmic reticulum and increased mitochondria and lysosome, which sug-gesting the reactive processes of the Schwann cells.

Frequent occurrence of denervated Schwann cell clusters suggested the considerable decrease of un-myelinated fibers. The possible consideration on morphogenesis of amyloid fibrils in the peripheral nerves of this disorder concluded to be different from these of other organs such as kidney, liver and spleen and of the experimental amyloidosis in animals.