Continuous muscle spasm in intramedullary tumours of the neuraxis

Clinical neurophysiology of cranial nerve disorders

Electrophysiologic techniques are available to measure many of the cranial nerves. The procedures can be done using equipment available in standard clinical neurophysiology laboratories. These studies can aid in localization of cranial nerve lesions as well help identify the underlying pathology and possibly aid in prognosis. The trigeminal pathways can be measured using the blink and masseter responses. The facial nerve is measured by the blink response and by direct facial stimulation; techniques such as lateral spread can identify specific abnormalities. The spinal accessory nerve is measured using nerve conduction techniques. Needle examination can be routinely performed on muscles innervated by cranial nerves V, VII, X, XI and XII. These studies reliably measure the functional integrity of cranial nerves and their central pathways. Intraoperative monitoring of the cranial nerves is useful in certain surgeries. This chapter reviews current techniques used to evaluate cranial nerves, emphasizing the methods available in most clinical neurophysiology laboratories.

Electrophysiological Evaluation of Cranial Neuropathies

BACKGROUND

Cranial nerve abnormalities occur frequently in both focal and diffuse neurologic disorders and can be evaluated by electrophysiological techniques available in most clinical neurophysiology laboratories.

REVIEW SUMMARY

The optic nerve is evaluated by visual evoked potentials. Measurements of latency, amplitude, and waveform morphology are especially useful in detecting demyelinating lesions. Brain stem auditory evoked potentials evaluate the auditory portion of the eighth cranial nerve. Using an auditory stimulus, a number of waveforms are generated, and changes in the normal patterns of response can detect abnormalities. Assessment of the trigeminal and facial nerves is done using a series of electrical stimulation techniques including the blink, masseter, and masseter inhibitory reflexes and facial motor nerve conduction studies. The blink reflex detects lesions of the first division of the trigeminal nerve and the facial nerve. The masseter reflex evaluates the third division of the trigeminal nerve. Changes in responses are measured and, using a combination of these techniques, localization of lesions at specific sites can be made. Accessory motor nerve conduction is useful not only in focal nerve injury, but repetitive stimulation on the accessory and facial nerves is used in diagnosing neuromuscular junction disorders. In addition, many of the voluntary muscles innervated by the cranial nerves are accessible to needle electrode examination, and evaluation can aid in identification of focal nerve lesions, as well as diagnosis in diffuse nerve and muscle disorders.

CONCLUSION

Electrophysiological techniques offer reliable means of measuring the integrity of the cranial nerves and their central pathways.

Facial myokymia associated with an isolated lesion of the facial nucleus

We report on a patient with transient facial myokymia. He had an isolated lesion of the right facial nucleus in the pontine tegmentum. Facial myokymia is a rare symptom and its pathogenesis is not known. Our case had a very localized lesion and we attempted to determine the case of the facial myokymia.

Facial myokymia and spastic paretic facial contracture as the result of anaplastic pontocerebellar glioma

The case of a 36-year-old man who sought treatment of right facial myokymia and spastic paretic facial contracture is reported. Computed tomography and magnetic resonance imaging revealed a tumor located in the right cerebellar peduncle and the right dorsal pons bulging into the fourth ventricle. After microsurgical partial resection of the mass, which was verified histologically as an anaplastic glioma, facial myokymia initially ceased. The vermicular rippling movements were less intense upon recurrence and could be controlled by low-dose dexamethasone in the further course, when magnetic resonance imaging showed an interstitial pontine edema after percutaneous radiation therapy. It is assumed that facial myokymia and spastic paretic facial contracture were generated by ectopic activity due to alterations in the microenvironment at the intrapontine portion of the axons of the seventh nerve caused by the compressive effect of the tumor and later by edema.

AAEM case report #21: hemifacial spasm: preoperative diagnosis and intraoperative management

A 75-year-old man developed progressive involuntary hemifacial spasm. Electrophysiologic evidence of abnormal cross-transmission between neurons of the facial nerve was demonstrated. Electrodiagnostic studies were used to confirm the diagnosis preoperatively and determine the adequacy of vascular decompression of the facial nerve intraoperatively.

Myokymia of the tongue in a case of brainstem tumour that simulated motor-neuron disease

The diagnosis of a brainstem tumour, which presented as progressive bulbar palsy that resembled motor-neuron disease, was suspected because of the rare electromyographic finding of myokymia of the tongue, and was confirmed by magnetic resonance imaging.

Segmental rigidity and spinal myoclonus as a paraneoplastic syndrome

A 68 year old woman is described with persisting muscular rigidity of the left lower leg together with transient myoclonic jerking in the left quadriceps muscle. Six weeks after onset a small cell carcinoma of the lung became manifest. With radiotherapy and chemotherapy complete remission was achieved. Segmental muscular spasm improved at the same time. Necropsy revealed loss and degeneration of alpha-motor neuron cells at one side of the anterior horn of the lumbar enlargement. This case may represent another manifestation of paraneoplastic subacute motor neuronopathy.

Facial myokymia in the course of a pontine tumor

A patient with facial myokymia, suffering from an infiltrating grade II astrocytoma originating within the pons with vegetations invading the cerebellopontine angle, was studied clinically and electromyographically from 1973 to 1979. The myokymias started in the muscles of the right side of the face and later spread to the left side. The latter point is worth noting because the myokymias of the left side were detectable by EMG but not by inspection. They preceded clinical and instrumental evidence of a contralateral spread of tumoral damage to the brainstem. From the physiopathogenetic angle they point up the importance of a mechanism of hyperexcitability and release of the facial motoneuronal pool. The results of the EMG study suggest that the persistence of myokymia, its association with an ingravescent neurogenic impairment of the facial musculature and its polymorphism in the course of pontine tumors are more reliable features than their discontinuity and rhythmicity.