Difference between revisions of "1° Caso clínico: Espasmo hemimasticatorio"

=== Ephaptic transmission ===

With a little effort and patience on the part of passionate readers who have followed the entire logical path, sometimes apparently off topic, we have reached a clinical picture in which the code to be decrypted is inherent in neuromotor damage. Consequently, the access keys to the code, the one that figuratively corresponds to the exact decryption algorithm, would correspond to the right choice of the neuromotor damage detector test.   

This is a point where it is essential to infer the clinician's intuition because finding the right algorithm to decrypt the code, after the aforementioned filter steps that have been described to wash away the interference of assertions, means at least choosing the right dictionary, for example, that of the image (MR of the brain rather than the neck); acoustic and vestibular evoked potentials (if a vestibular scwannoma is suspected) or trigeminal electrophysiological study (if more than one trigeminal involvement is suspected).

In this clinical iter that we have presented, the choice of the clinician to follow the electrophysiological trigeminal roadmap from which the positivity of the <math>\bar{\gamma_n}=1</math> assertions have already been derived, therefore, having already defined a picture of serious anomaly of absence of the jaw jerk and of the silent period masseterino on the right side of the patient will have to understand if the damage is intracranial or extracranial.

To do this, the clinician uses an electrical stimulation test of the masseter nerve in infratemporal fossa called <math>M-wave</math> on the masseter muscle with simultaneous recording of the heteronymous <math>H-wave</math> on the temporal muscle<ref>{{cita libro  

  }}</ref> and a bilateral transcranial electrical stimulation of the trigeminal motor roots called, precisely, <math>_bRoot-MEPs</math><ref name="fris1992">{{cita libro  

The right masseter nerve was electrically stimulated in the infratemporal fossa (see clinical procedure chapter: [[Encrypted code: Ephaptic transmission]]) with a technique similar to that described by Macaluso & De Laat (1995).<ref>Macaluso G, De Laat A. [https://pubmed.ncbi.nlm.nih.gov/8773249/ H-reflexes in masseter and temporalis muscle in man. Experimental] Brain Research. 1995;107:315–320. [PubMed] [Google Scholar] [Ref list]</ref> Square cathode pulses (0.1 ms) generated by an electrical stimulator (Neuropack X1, Nihon Kohden Corporation, Tokyo, Japan) were delivered through a Teflon-coated monopolar needle electrode (TECA 902-DMG25, 53534) with a tip non-isolated (diameter 0.36 mm; area 0.28 mm2) inserted 1.5 cm through the skin below the zygomatic arch and anterior to the temporomandibular joint in the infratemporal fossa with electrical shocks of 0.5 - 5 mA, and 0.1 ms. The anode was a surface non-polarizable Ag-AgCl disc electrode (OD 9.0 mm) positioned over the ipsilateral ear lobe. Electrical stimulation of the masseter nerve never produced pain, and the subjects only perceived muscle contraction. The correct position of the stimulation electrodes was monitored throughout the experimental session by checking online the size of the M wave in the masseter muscle. The signals were recorded by placing surface electrodes on the masseter and temporal muscles and filtered at 10-2000Hz and by concentric needle electrodes inserted into the anterior temporal muscle.   

{{Q2|The response in the right masseter was clearly delayed but relatively symmetrical in amplitude between sides. (Fig. 9)}}

The trigeminal root was stimulated transcrally through high voltage, low impedance through an electrical stimulator (Neuropack X1, Nihon Kohden Corporation, Tokyo, Japan)) with the anode electrode positioned at the apex and the cathode approximately 10 cm laterally from the apex along a line vertex acoustic meatus. The electric field is believed to excite the trigeminal motor nerve fibers via the trancranial route, near their exit from the skull.<ref name="fris1992" /><ref>G Frisardi, P Ravazzani, G Tognola, F Grandori. [https://pubmed.ncbi.nlm.nih.gov/9467995/ Electric versus magnetic transcranial stimulation of the trigeminal system in healthy subjects. Clinical applications in gnathology.] J Oral Rehab.1997 Dec;24(12):920-8.doi: 10.1046/j.1365-2842.1997.00577.x.</ref> Also in this case, the response in the right masseter was markedly delayed (3.5 ms on the right side 2 ms on the left and dispersed. amplitude of the M-wave.

[[File:TCS Lupo edited.jpg|center|thumb|600x600px|'''Figure 9:''' The responses evoked by stimulation of the masseter nerve M-wave and the trigeminal Root-MEPs are clearly delayed on the right side while maintaining the amplitude relatively symmetrical.]]

Having highlighted, through the execution of the <math>M-wave</math> and <math>_bRoot-MEPs</math> test, a delay in the conduction speed of the trigeminal nerve fibers generates the suspicion that it is a focal demyelination. This indicates that the problem is to be referred to the nervous component rather than to the muscular one, therefore, our attention should focus on the type of focal demyelination, extent of damage and presumably localization of the damage. The differential diagnosis at this point focuses on the type and area of the demyelinating damage, for example, if it is a damage exclusively referred to the masseterine motor nerve or the motor nerve of the temporal muscle is also involved, important for treatment with botulinum endotoxin. To resolve this doubt it is necessary to evoke a heteronymous <math>H-wave</math> response from recording on the temporal muscle.

The arrangement is similar to that previously described with regard to the <math>M-wave</math> with the variant that the temporal muscle is recorded simultaneously with the stimulation of the masseterine nerve in the intratemporal fossa by a bipolar needle electrode. The stimulation must be gradually adapted in order to evoke both a <math>M-wave</math> from the masseter that a heteronymous <math>H-wave</math> from the temporal muscle.

In our patient Mary Poppins, unfortunately, the neuromotor situation is quite complex and serious because to the infratemporal stimulation of the masseteral nerve we have a direct evoked response on the muscle ipsilateral to the stimulation (figure 10; <math>M-wave</math>) and at the same time not a heteronymous response (figure 10; <math>H-wave</math> ) on the temporal muscle but rather a tonic asynchronous activity (Figure <math>E</math>)

This neurophysiopathological phenomenon is called 'Ephaptic transmission' and allows us to confirm the presence of demyelinating lesions also of the motor nerve of the temporal muscle.

As previously mentioned and in order not to burden the topic, the detailed description of the 'Hephaptic' phenomenon will be treated in the chapter '[[Encrypted code: Ephaptic transmission]]' in order to better understand the physiological responses of heteronymous <math>H-wave</math> by pathological ones.

[[File:Hephaptic edited.jpeg|center|thumb|600x600px|'''Figure 10:''' On the right indicated with EMG the recording of the motor unit discharge on the right masseter at the time of the spasm is shown while on the right below indicated with M-wave we can see two motor potentials evoked by the electrical stimulation in infratemporal fossa recorded on the masseter. With H-wave it is possible to note the recording of the heteronomous H-wave on the temporal ipsilateral to the stimulation.]]

=== Conclusions ===

Following this step by step path we have demonstrated a peripheral motor nerve injury as originally proposed by Kaufman.<ref name="kauf">Kaufman MD. [https://pubmed.ncbi.nlm.nih.gov/7436363/ Masticatory spasm in facial hemiatrophy]. Ann Neurol 1980;7:585-7.</ref> Conduction studies have shown a slowing of conduction in the extracranial course of masticatory nerve fibers without a reduction in the amplitude of <math>M-wave</math> and obviously EMG signs of chronic denervation. The temporal muscle biopsy appeared histologically normal.

{{Q2|These results indicate axon-sparing demielination.}}  

The absence of the jaw jerk on the diseased side indicates damage to the large diameter afferent fibers ({{:F:A-alpha}}) from the neuromuscular spindles. A lesion of few afferents {{:F:A-alpha}} could easily abolish the jaw jerk.<ref>Cruccu G, Inghilleri M, Fraioli B, Guidetti B, et al. [https://pubmed.ncbi.nlm.nih.gov/3561775/ Neurophysiologic assessment of trigeminal function after surgery for trigeminal neuralgia]. Neurology 1987; 37:631-8.</ref>

Muscle nerve damage would not be explained only because patients with Hemimasticatory Spasm (HMS) do not have sensory disturbances but also because they often only have spasms in one or two levator mandibular muscles. These observations argue against damage to the motor root or to the intracranial portion of the mandibular nerve where the motor bundles are closely grouped,<ref>Pennisi E, Cruccu G, Manfredi M, Palladini G. [https://pubmed.ncbi.nlm.nih.gov/1795166/ Histometric study of myelinated fibers in the human trigeminal nerve]. J Neurol Sci 1991;105:22-8.</ref> favoring damage to the individual muscle nerves that pass through the infratemporal fossa.

The mechanism of involvement of facial paroxysmal involuntary activity has been discussed by Kaufnan<ref name="kauf" /> and by Thompson and Carroll<ref>Thompson PD, Carroll WM. [https://pubmed.ncbi.nlm.nih.gov/6842234/ Hemimasticatory spasm: a peripheral paroxysmal cranial neuropathy?] J Neurol NeurosurgPsychiatry 1983;46:274-6.</ref> who emphasized the close similarity between hemimasticatory and hemifacial spasm.

In EMG, these prolonged spasms fit perfectly into the description of cramps, that is, discharges of irregular motor units that progressively increase, leading to the recruitment of much of the muscle of synchronous discharges at speeds of 40 to 60 Hz.<ref>Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 2nd edn. Philadelphia: FA Davis 1989.</ref> Common to hemifacial spasm and cramps however, ectopic EMG activities can also be detected.

This could be responsible for the high frequency of EMG discharges at a frequency of 100-200 Hz and the synchronization of the entire muscle or multiple muscles, and post-activity. The synchronization could be explained by the lateral spread of discharges from adjacent nerve fibers,<ref>Nielsen VK. [https://pubmed.ncbi.nlm.nih.gov/6322049/ Pathophysiology of hemifacial spasm: II. Lateral spread of the supraorbital nerve reflex]. Neurology 1984;34:427-31.</ref><ref>Thompson PD. Stiff people. In Fahn S, Marsden CD, eds. Movement disorders 3. London: Butterworths, 1993: 367-99.</ref> generating a local re-excitation circuit. Posthumous EMG activity consists of paroxysmal discharges that may follow a voluntary orthodromic contraction or antidromic impulses,<ref>Auger RG. [https://pubmed.ncbi.nlm.nih.gov/573406/ Hemnifacial spasm: clinical and electrophysio- logic observations.] Neurology 1979;29: 1261-72.</ref><ref name="niels">Nielsen VK. [https://pubmed.ncbi.nlm.nih.gov/6322048/ Pathophysiology of hemifacial spasm: I. Ephaptic transmission and ectopic excitation.] Neurology 1984;34:418-26.</ref> and is attributed to self-excitation of the same axons after the passage of an impulse.

In our patient Mary Poppins we observed a synchronization of the whole or a large part of the muscle involved in the spasm (fig 10, EMG); the self-excitation is evidenced by the recording of the evoked discharges following the response of the stimulation of the chewing nerves (Fig. 10, E). These results support the hypothesis that spontaneous activity 'arises' in a demyelinated peripheral nerve, a phenomenon called hepaptic.<ref name="niels" />

In conclusion, the patient was affected by 'Hemimasticatory Spasm' mainly focused on the right masseter muscle but with indirect diffusion of the phenomenon to the right temporal muscle probably due to hepaptic activity due to the demyelination of the masticatory motor nerves in the infratemporal fossa. Botulinum endotoxin therapy was started immediately with total regression of the disease 10 years later.

{{Q2|But how do we get to decrypt a machine language code?|we will try to describe it in the chapter 'Crypted code: Ephaptic transmission' at the end of the section 'Hemasticatory spasm'}}