Making a reliable prognosis in early stages of acute facial paralysis is difficult. Because the rate of regeneration is related to the degree and rate of denervation, serial electrical tests are often performed. The Hilger Model H3 is an effective and economical method of clinical evaluation for patients with facial paralysis.
Electrodiagnostic testing for patients with facial paralysis.
MAXIMAL STIMULATION TEST (MST)
Recording sites of the frontal, orbital, and marginal branches of the facial nerve are selected. The stimulator is applied to the nerve branch at that intensity which produces a just-visible twitch. The current is then increased to one-to two mA above the threshold to obtain a supramaximal response. Each branch is stimulated on both the affected and non-affected side of the face, and response is compared.
NERVE EXCITABILITY TEST (NET)
Upper and lower divisions of the facial nerve are selected for stimulation. Current is applied in increasing amounts until the onset of twitching of one or more of the facial muscles. The difference between the normal and paralyzed sides indicates the degree of denervation.