Nerve conduction study in rehabilitation of patients with residuals and complications of long-standing Bell's palsy
Authors: Pashov A. 
Published: February 2019

From every 100 cases of Bell’s palsy (idiopathic peripheral facial palsy) from 15 to 30 will not recover completely. Some residuals will remain, and some complications will develop. As residuals, one can name weakness of facial muscles, asymmetry of facial expressions, distortion of taste, hyperacusis, dry eye. Possible complications of long-standing Bell’s palsy (BP) are also numerous: contractures of facial muscles, pathological synkinesis, mass movements, crocodile tears, facial pains, headaches, emotional disbalance etc.

Unresolved cases of Bell’s palsy require rehabilitation programs that will address both the issues of general nerve regeneration, complications and irregularities in mimetic movements, and psycho-emotional state of long-standing Bell’s palsy patients. There are several methods and systems to assess the condition of facial nerve and functioning of facial muscles. These scales and systems are either therapist- or patient-graded: House-Brackmann Facial Grading system, Sunnybrook Facial Grading system, Facial Clinimetric Evaluation Scale (FaCE Scale), Synkinesis Assessment Questionnaire (SAQ) and several others.

At the same time, to compose a well-balanced and focused rehabilitation program, next to subjective assessments and test-photos of standard facial expressions, it is important to have an objective, instrumentally-measured picture of facial nerve recovery, as well as of the physiological ability of mimetic muscles to perform facial movements, to reflect emotions and to produce articulated speech.

In that respect, the surface EMG or Nerve Conduction Study (NCS) is the modality of choice. NCS-examination is non-invasive and is relatively easy to perform. It records Compound Muscle Action Potentials (CMAPs) in response to external stimulation. The analysis of recorded graphs allows to evaluate the level of regeneration and maturity of recovering axons in main branches of the facial nerve.

At the same time, the standard protocol of NCS does not offer a detailed assessment of each particular muscle of facial expression. It also requires additional time to swap the active electrode position when changing stimulation side from right to left and vice versa.

At Crystal Touch Bell’s palsy clinic, we have developed an amended NCS protocol that addresses all mentioned issues. To allow a more detailed assessment of facial muscles, we have added mm.zygomatici (major et minor) and m.depressor anguli oris to the list of measured facial muscles.

In order to perform a more focused stimulation and to receive a more “clean” motor responses from facial muscles, we changed the position of stimulating electrode. In the standard protocol, stimulating electrode is placed either pre- or post-auricularly. In Crystal Touch protocol, we position the stimulating electrode above each particular nerve branch that innervates the measured muscle. Therefore, we use six positions of stimulating electrode that correspond to the six measured facial muscles: m.frontalis, m.orbicularis oculi pars superioris, m.nasalis et m.levator labii superioris, mm.zygomatici (major et minor), m.orbicularis oculi pars superioris, m.depressor anguli oris et m.mentalis.

To save time required for the examination, instead of placing reference electrode on the nasal bridge (standard protocol), we use contralateral electrode over the same as measured muscle, as a reference electrode. As there are no anastomoses between left and right facial nerves, stimulation of facial nerve on one side will not evoke CMAPs in contralateral facial muscles. This simple amendment allows to save about 15% of total time required for the examination.

In this article we also briefly touch the following issues: distortion in reciprocal inhibition of facial muscles-antagonists, forming of the pathological mimetic patterns in the motor cortex due to lack of proprioceptive feedback during long recovery, and the necessity to further investigate from the electrotechnical, engineering and functional point of view the hypothesis of aberrant regeneration as possible cause of facial synkinesis.