In addition to the aforementioned "flaccid" paralysis, there are also spastic movement disorders of the muscles innervated by the facial nerve. An example of this is "hemispasm facialis" which causes involuntary contractions of large parts of the mimetic musculature. Another example, blepharospasm, affects the orbicularis oculi muscle. It involuntarily shows an excessive tone either in phases or continuously (i.e. a cramp not wanted by the patient, but often perceived as extremely disturbing). As a result, the affected eye appears smaller than that of the opposite, unaffected side. Disturbing unwanted twitches also occur, which are often perceived as extremely unpleasant by the patient. Psychological tension and stress often aggravate the symptoms and in turn lead to avoidant behavior on the part of the affected patients.  The etiology of this disease has not yet been fully clarified [1,2]. However, it is assumed that an overexcitability of the facial nerve due to an compression of the nerve by a blood vessel near the exit zone from the truncus cerebri is the most probable cause[1,3]. The facial nerve in this so-called "root-exit zone" of the brain stem reveals some anatomical features that make it more prone to injury at this site (e.g. by compression of the nerve) [1,2]. Thus, the genesis of the nerve overreactability of the facial nerve is similar to that of another cranial nerve, the trigeminal nerve. Trigeminal neuralgia, a pain symptomatology suddenly shooting into the face, is also frequently based on pathological overexcitation of the trigeminal nerve by an adjacent arterial vessel.

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[11] Rosenstengel C, Matthes M, Baldauf J, Fleck S, Schroeder H. Hemifacial spasm: conservative and surgical treatment options. Dtsch Arztebl Int. 2012 Oct;109(41):667-73. doi: 10.3238/arztebl.2012.0667. Epub 2012 Oct 12. PMID: 23264807; PMCID: PMC3487151.