Drooping of the upper eyelid and narrowing of the palpebral fissure associated with peripheral facial nerve palsy

摘要

末梢性顔面神経麻痺では眼輪筋麻痺による眼裂の拡大だけでなく前頭筋麻痺による眼裂の狭小が重要な所見である。顔面神経支配の前頭筋は上眼瞼の挙上に関して補助的に働くので, その麻痺により上眼瞼の下垂 (眼瞼下垂) が起こると考えられる。このため, 前頭筋麻痺による眼瞼下垂が軽度であれば眼輪筋麻痺による眼裂拡大が前景に立つが, 重度になると逆に眼裂狭小が起こることになる。この眼裂狭小が時に非常に重度となることから, 上眼瞼の挙上に関する前頭筋の役割は極めて重要であると思われる。このことを説明するために, 上部顔面の皮膚の状態に注目した。すなわち, 高齢者では上眼瞼や額の皮膚の弛緩によって上眼瞼の下垂 (偽眼瞼下垂 pseudoptosis) が起こりやすいが, 前頭筋の働きによりこれが代償されると眼裂狭小にならない可能性がある。このような ''潜在化'' した眼裂狭小がある場合に前頭筋麻痺が起こると眼裂狭小が重度になると思われる。前頭筋麻痺による眼瞼下垂と上眼瞼挙筋麻痺による眼瞼下垂を鑑別する方法として, 験者の手で他動的に麻痺側の眉毛を釣り挙げて眼裂の大きさの変化をみる「眉毛挙上試験」が単純であるが非常に有用と思われた。 / Widened palpebral fissure on the affected side has been regarded as one of the hallmarks of peripheral facial nerve palsy. Contrary to this textbook description, however, peripheral facial nerve palsy often causes narrowing of the palpebral fissure on the affected side, which probably results from drooping of the upper eyelid because of weakness of the frontal muscle. This narrowing showed a varying degree of drooping of the eyebrow. There were patients with a svere degree of narrowing. This indicates that the frontal muscle which has been considered as an accessory muscle, occasionally plays a very important part in eyelid elevation. We suspect that this is closely related to the skin condition of the upper face. Some elderly people have excessively loose skin of the upper eyelid or forehead, resulting in 'masked' palpebral narrowing. In such a situation, occurrence of frontal muscle weakness can produce severe palpebral narrowing. With the patient looking straight ahead, the change of palpebral narrowing was evaluated when the eyebrow on the affected side was lifted manually by the examiner (eyebrow lifting test). In all of the peripheral facial nerve palsy group palpebral narrowing disappeared when the eyebrow on the affected side was lifted slightly, whereas in all of the levator palsy group palpebral narrowing remained unchanged, even when the eyebrow was lifted to its maximal extent. The 'eyebrow lifting test' is simple but very helpful in differentiating between two types of palpebral narrowing due to weakness of the frontal muscle and levator palpebrae superioris.