Child's Nerv Syst (1992) 8:126-128

mGlqS 9 Springer-Verlag 1992

Value of the facial nerve latency test in the prognosis of childhood Bell's palsy Vassillios G. Danielides 1, Antonios I". Skevas 1, Kanaris Panagopoulos 2, and Ioannis Kastanioudakis 1 1 Department of Otolaryngology and z Department of Neurosurgery, General Hospital, University of Ioannina, P.O.B. 1186, GR-45110 Ioannina, Greece Received May 2, 1991

Abstract. In the present study we evaluated the facial nerve latency test (FNLT) as a prognostic tool in cases of childhood Bell's palsy. Twenty-five children aged 4 - 1 4 years were studied. We divided our subjects into three groups according to duration of latency time (LT). G r o u p A patients had an LT within the normal range, with average of 3.27 ms, group B a slightly prolonged LT averaging 5.7 ms, and group C a markedly prolonged LT averaging 10.5 ms. Analysis of the recovery index by group showed that group A patients experienced complete and quick recovery, while in group B 50% had complete but delayed recovery and 50% slightly impaired facial nerve function, and in group C 50% had slightly impaired function and 50% incomplete recovery. The more prolonged the LT, the worse the clinical results. The F N L T is thus a valuable prognostic tool in cases of Bell's palsy in childhood.

Key words: Bell's palsy - Facial nerve latency test - Conduction time test - Electrodiagnosis of facial nerve

In cases of recently established idiopathic paralysis of the facial nerve (Bell's palsy) in childhood, the main questions are about prognosis. Is the damage reversible? Will functional recovery take place, and if so, to what extent and when? To answer these questions, somebody has to determine the degree of the neuronal damage as precisely as possible, by establishing that the nerve is suffering from either neurapraxia, axonotmesis, or neurotmesis. To define the functional status of the nerve, the following electrophysiological tests are used: i. The nerve excitability test (NET) 2. The maximum stimulation test (MST) 3. Electroneurography (ENG) 4. Electromyography (EMG) 5. The Facial nerve latency test (FNLT) Offprint requests to: A. T. Skevas

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Fig. 1. The FNLT records the time (in milliseconds) between the application of an electrical stimulation to the trunk of the facial nerve and the start of the first compound muscle action potential

The F N L T is a neurophysiological test which records the time (in milliseconds) between the application of electrical stimulation to the trunk of the facial nerve and the start of the first c o m p o u n d muscle action potential (Fig. 1). This includes the conduction time, the time to cross the end plate, and the time to cross the synapse. In the present study we evaluated the contribution of the F N L T in the determination of the degree of neuronal damage in cases of idiopathic facial paralysis in childhood.

Patients and methods Patients

We investigated 25 children from 4 to 14 years of age with idiopathic facial palsy. Children seen after the 4th day from the onset of the palsy were not included. We also excluded patients suffering from juvenile diabetes mellitus and chronic renal insufficiency. Methods

We used an Amplaid MK10 apparatus to perform the FNLT. The bipolar stimulating electrode was applied with the anode between the ramus of the mandible and the mastoid and the cathode in front of the tragus of the ear. In this way the stimulation was applied to the trunk of the nerve as it exits the stylomastoid foramen. As recording electrode we used a bipolar surface electrode. The recording electrode was applied over the nasobuccal fissure while the reference electrode was applied over the ipsilateral labial corner. Finally, the ground electrode was placed at some distance, e.g., in the contralateral frontal area or ipsilateral ear lobule.

127 Table 1. Classification system for reporting results of facial nerve recovery [2]

Degree of injury

Grade

Definition: recovery results

Compression, neuropraxia (1~

I

Normal, symmetrical function in all areas

Neuropraxia - axonotmesis (1~ ~

II

Slight weakness noticeable only on close inspection. Complete eyelid closure with minimal effort. Can raise eyebrow. Contracture or spasm absent, synkinesis may be barely noticeable

Axonotmesis - neurotmesis (2~ ~)

III

Obvious weakness, but not disfiguring. May not be able to raise eyebrow. Complete eyelid closure and strong but asymmetrical mouth movement with maximal effort. Obvious, but not disfiguring synkinesis, mass movement of spasm

Neurotmesis, sheath intact (3 ~)

IV

Obvious disfiguring weakness. May not be able to raise eyebrow. Incomplete eyelid closure and asymmetry of mouth with maximal effort. Severe synkinesis, mass movement, spasm

Nerve partially severed or crushed (3~ ~

V

Motion barely perceptible. Incomplete eyelid closure slight movement corner mouth. Synkinesis, contracture, and spasm usually barely visible

Nerve transected (5~)

VI

No movement, loss of tone, no synkinesis, contracture, or spasm

Table 2. Division into groups by duration of latency time

Group

Range

A B C

mean

2.4-4 ms 4 - 7 ms 8-14 ms

No. of patients 0=25)

3.27 5.7 10.5

17 4 4

Table 3. Latency time and grade of functional recovery of facial nerve [2] Group

Grade of recovery I

II

A

17

B

2

C

III

IV

No. of patients (n=25) V

VI

17 2

2

4

2

4

The investigation started with application of a supramaximal stimulation of 0.i-0.2 ms duration over the trunk of the facial nerve with a frequency of less than 1 bit/s. The intensity varied from 0 to 25 Ma and was gradually increased to the point at which a strong stimulation was achieved beyond which the latency time (LT) and the width of the waveform of the muscle action potential remained stable. To evaluate the results we referred to established normal values of LT [6]. We performed the FNLT from the first 24 h of the onset of the palsy and repeated it every 2 days for the first 10-14 days, this being the higher risk period for nerve degeneration. The test was repeated after 15 days and once a month thereafter until full recovery took place or a full year had elapsed from the onset of the palsy. Beyond 1 year after onset we thought examination purposeless because no further improvement could be expected. All Patients were subjected to the same therapeutic regimen with 25-30 mg prednisolone daily together with a vitamin B complex. We employed the House system for grading of functional recovery of the facial nerve in order to have an objective assessment of the functional result and thus to assess the value Of the FNLT (Table 1) [2].

Results

T h e y o u n g p a t i e n t s were d i v i d e d into three g r o u p s acc o r d i n g to LT o n the affected side o f the face. Table 2 shows these g r o u p s . T h e first g r o u p i n c l u d e d 17 p a t i e n t s in w h o m the LT v a r i e d f r o m 2.4 m s to 4 ms, w i t h a n a v e r a g e o f 3.27 ms. This is w i t h i n the n o r m a l range. I t refers to first degree n e u r o n a l d a m a g e (the least severe), e.g., n e u r o p r a x i a . I n this g r o u p full f u n c t i o n a l r e c o v e r y t o o k p l a c e a n d the p r o g n o s i s is t h e r e f o r e excellent [6, 7] (Fig. 2 a). T h e s e c o n d g r o u p c o n s i s t e d o f 4 p a t i e n t s in w h o m the LT was slightly to m o d e r a t e l y p r o l o n g e d , v a r y i n g between 4 m s a n d 7 ms, w i t h a n a v e r a g e o f 5.7 ms. A l t h o u g h this is a small g r o u p for statistical analysis, t h o s e LT values d o i n d i c a t e m o r e serious d a m a g e o f the facial nerve, e.g., a x o n o t m e s i s (Fig. 2 b , c). I n the t h i r d g r o u p there were 4 p a t i e n t s in w h o m the LT was m a r k e d l y to e x t r e m e l y p r o l o n g e d , with values b e t w e e n 8 m s a n d 14 ms. T h e s e values i n d i c a t e severe n e u r o n a l d a m a g e , e.g. n e u r o t m e s i s o r a c o m b i n a t i o n o f a x o n o t m e s i s a n d n e u r o t m e s i s . N o full r e c o v e r y was exp e c t e d in this g r o u p [6]. T h e classification allows for a f o u r t h g r o u p in w h i c h there is c o m p l e t e a b s e n c e o f the a c t i o n p o t e n t i a l [1, 6], a n d in this g r o u p the p r o g n o s i s is e x t r e m e l y p o o r . W e d i d n o t have a n y p a t i e n t s in this g r o u p , w h i c h is m o r e c o m m o n l y seen after surgery f o r a c o u s t i c nerve t u m o r s , tum o r s o f the p a r o t i d gland, a n d , very seldom, in cases o f Bell's palsy. H a v i n g the F N L T as criterion, we a t t e m p t e d to correlate the results o f this to the degree o f f u n c t i o n a l r e c o v e r y o f the facial nerve, using the H o u s e classification [2] (Table 3). A s is e v i d e n t f r o m this table, the 17 g r o u p A p a t i e n t s w i t h LT within n o r m a l r a n g e all h a d full funct i o n a l r e c o v e r y o f the facial nerve w i t h i n 1 - 2 m o n t h s f r o m the time o f onset. O f the 4 p a t i e n t s b e l o n g i n g to g r o u p B, with a slightly to m o d e r a t e l y p r o l o n g e d LT, 2 h a d g r a d e I full f u n c t i o n a l recovery, b u t the time t a k e n

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tages. Its value lies in that it can be performed from the 1 st day of the palsy. In this conclusion Joachims et al. [3] concur; they found the F N L T to be similarly potent in prognosis. This finding clearly signifies that the F N L T has an advantage in prognostic value over other electrophysiological tests, all of which can give answers a b o u t prognosis after 48 72 h f r o m the onset of the palsy - the time necessary for the Valerian degeneration to progress from the petrous segment of the facial nerve to the stylomastoid foramen where the electrical stimulation is applied. The values that we implied as normal after the age of 3 years are the same as established in the adult population in a previous report [6]. Langworthy and Taverner [4] reported on the basis of studies in normal adult individuals that the upper normal limit of LT should be 4 ms. Waylonis and Johnson [8] considered 3.4_+ 0.8 ms as the norm. In a previous work we studied 80 normal adult individuals and found the average normal LT to be 3.2 + 0.35 ms [6]. We had noticed that there were slight variations between investigators in regard to the average normal value. These variations might be due to the use of different apparatuses and different placements of the electrode. In subjects below the age of 3 years the use of considerable variations of the normal LT have been observed, especially in newborns. After the age of 3 years the normal LT becomes stabilized [8]. The accuracy of the F N L T as a prognostic factor reaches 94% according to a study that we did in 131 patients [1]. In conclusion we can say that: 1. The F N L T is an objective test which is performed in a short time and does not require the full cooperation of young patients.

Facial nerve

Fig. 2 a-c. Latency times: a normal, b slightly prolonged, e moderately prolonged

2. The F N L T can be carried out from the first 24 h of the palsy and can establish the degree of neuronal damage as well as predict the outcome with a remarkably high percentage of accuracy.

was a b o u t 4 months. The other 2 patients in the group had grade II functional recovery. Finally, of the four group C patients, with an extremely prolonged LT, 2 had grade II (incomplete) functional recovery while the remaining 2 had only grade III recovery. N o n e of the group C patients had grade I recovery.

3. The F N L T should be repeated at least every 2 days for the first 10 14 days (the high risk period for nerve degeneration).

Discussion

1. Danielides V (1990) The contribution of electrodiagnostic tests in evaluation and location of damage of the facial nerve. Doctoral thesis, Ioannina, Greece 2. House JW (1983) Facial nerve grading system. Laryngoscope 93:1056-1069 3. Joaehims HZ, Bialik V, Eliachar I (1980) Early diagnosis in Bell's palsy. Laryngoscope 90:1705-1708 4. Langworthy EP, Taverner D (1963) The prognosis in facial palsy. Brain 86:465 5. Seddan HJ (1943) Three types of nerve injury. Brain 66:237-288 6. Skevas A, Danielides V, Assimakopoulos D (1990) The role of the facial nerve latency test in prognosis of Bell's palsy. Laryngoscope, vo1100, no 10 7. Sunderland S (1978) Nerve and nerve injuries. Churchill-Livingstone, London, pp 88-89, 96-97, 133 8. Waylonis GW, Johnson EW (1964) Facial nerve conduction delay. Arch Phys Med Rehab 45:539

It is impossible accurately to assess the functional status of the facial nerve in the various stages of the development and progress of a facial palsy by clinical examination alone. Physical examination by itself cannot give information a b o u t the precise degree of neuronal damage and the prognosis of the disease. The value of clinical examination decreases still further when we are dealing with children who are uncooperative and difficult to examine. The contribution of the electrodiagnostic tests in the assessment of neuronal damage, evolution, and prognosis in facial palsy in childhood is great. In a previous study we concluded that a m o n g the various electrodiagnostic tests the F N L T has certain advan-

4. The m o r e prolonged the LT, the worse the prognosis. References

Value of the facial nerve latency test in the prognosis of childhood Bell's palsy.

In the present study we evaluated the facial nerve latency test (FNLT) as a prognostic tool in cases of childhood Bell's palsy. Twenty-five children a...
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