Hemifacial Spasm - Causes

Causes

Three theories exist to explain the facial nerve dysfunction found in hemifacial spasm. The first proposed theory is ephaptic transmission, which is electrical activity crossing from one demyelinated neuron to another resulting in a false synapse. The second theory involves abnormal activity of axons at the facial nerve root end zone secondary to compressive damage/demyelination.

The third theory or "Kindling theory" involves increased excitability of the facial nerve nucleus due to feedback from a damaged facial nerve.

It is generally accepted as compression of the facial nerve by vessels of the posterior circulation. In detail compression of the seventh cranial nerve by a dolichoectatic (a distorted, dilated, and elongated) vertebral artery is accepted to be the general cause of hemifacial spasm. Less than 1% of cases are cause by tumor. Hemifacial spasm is much more common in some Asian population.

Several families with hemifacial spasm have been reported, suggesting a genetic etiology or predisposition in some cases. There appears to be an autosomal dominant pattern of inheritance in these families with low penetrance, and except for a younger age at onset, the clinical features overlap with the idiopathic cases.Evaluation of single-nucleotide polymorphisms in genes related to vascular change causing compression of blood vessles did not show an association with hemifacial spasm. Clarifying the role of genetic susceptibility in hemifacial spasm may help to better understand the pathogenesis of this disease.