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Hemifacial spasm (HFS) is a rare neuromuscular disease characterized by irregular, involuntary muscle contractions (spasms) on one side (hemi-) of the face (-facial). The facial muscles are controlled by the facial nerve (seventh cranial nerve), which originates at the brainstem and exits the skull below the ear where it separates into five main branches. This disease takes two forms: typical and atypical. In typical form, the twitching usually starts in the lower eyelid in orbicularis oculi muscle. As time progresses, it spreads to the whole lid, then to the orbicularis oris muscle around the lips, and buccinator muscle in the cheekbone area. The reverse process of twitching occurs in atypical hemifacial spasm; twitching starts in orbicularis oris muscle around the lips, and buccinator muscle in the cheekbone area in the lower face, then progresses up to the orbicularis oculi muscle in the eyelid as time progresses.〔 The most common form is the typical form, and atypical form is only seen in about 2–3% of patients with hemifacial spasm. The incidence of hemifacial spasm is approximately 0.8 per 100,000 persons. This disorder occurs in both men and women, although it affects middle-aged or elderly women more frequently. Hemifacial spasm is much more common in some Asian populations.〔 It may be caused by a facial nerve injury, a tumor, or it may have no apparent cause. Individuals with spasm on both sides of the face are very rare. == History == The earliest descriptions about hemifacial spasm is by Shultze in 1875 and Gowers in 1899. The etiology of hemifacial spasm and location of the abnormality have been debated for more than a century.〔 Surgical treatment for hemifacial spasm in the early 20th century included neurolysis (destruction of nerve tissue), stretching the facial nerve (seventh cranial nerve), and high-pressure irrigation of the nerve with lactate ringer's solution. The medical regimens of that time involved injection of the nerve with ethanol, electrical stimulation, application of toxic compounds (nitrate of silver, zinc, arsenic, bromides) as well as medications such as Dilantin or other anticonvulsants.〔 Additional advances in understanding the etiology and improving treatments for hemifacial spasm did not occur until the mid-seventies. In 1977, 47 cases of hemifacial spasm underwent microvascular decompression of the facial nerve using the operating microscope. The results illustrated nerve-vessel conflicts (or cholesteatoma) to be located at the root exit zone of the facial nerve in all cases. The root exit zone is where the central glial axonal insulation of the nerve ends and the peripheral nerve axonal myelination begins. Biopsies of the root exit zone demonstrated degeneration of axons, denuded axis cylinder and interrupted myelin. The results of the experiment strengthened the theory that vascular compression of the facial nerve was the primary cause of hemifacial spasm, and proposed a specific region of the facial nerve where the effects of longstanding compression results in nerve dysfunction.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hemifacial spasm」の詳細全文を読む スポンサード リンク
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