Evaluation Guidelines Table132

Neuroimaging. Lesions of the medulla such as infarction or neoplasm, or extramedullary, intracranial lesions, are better visualized by magnetic resonance imaging (MRI) than by computer-assisted tomography (CT). Some lesions that involve bone, especially the skull base, may be detected by CT or radiographs, the latter usually requiring the neurologist to request special views of the base of the skull. Imaging should be employed to assist in defining lesion type when the clinical examination indicates an intracranial process.

Electrophysiology. Disorders of speech and swallow suspected to be due to neuromuscular disorders such as motor neuron disease or myasthenia gravis may be evident on electrophysiological testing. Repetitive stimulation on nerve conduction studies, and single fiber assessment of jitter may aid in the diagnosis of myasthenia. Electromyography (EMG) of the tongue or limb muscles may demonstrate denervation indicative of motor neuron disease. The location of a nerve lesion producing vocal cord paralysis may be established by EMG testing of the thyroarytenoid

TABLE 13-2 -- USEFUL TESTS IN THE EVALUATION OF DISORDERS OF CRANIAL N

ERVES IX AND X*

Neuroimaging

Electrophysiology

Fluid and

Tissue

Analysis

Neuropsychology Tests

Other Tests

Seven supranuclear lesions unilateral or bilateral

CT or MRI evidence of structural lesion, most commonly ischemic infarction of the frontal lobe.

EEG may demonstrate nonspecific abnormalities

Not applicable

Evidence of cognitive impairment

None

Nuclear lesions: lateral medulla

MRI evidence of ischemic infarcton. CT is not optimal imaging modality in this region. Angiographic evidence of impaired flow in the vertebral or basilar artenes

No findings

Not applicable

No abnormal findings

None

Proximal peripheral nerves: Cerebellopontine angle lesion

MRI or CT evidence of contrast enhancing mass lesion

Abnormal interwave separation (waves I-III, I-V) on brain stem auditory evoked potential

Not applicable

None

None

Middle peripheral nerve lesion at base of skull or nasopharynx

MRI or CT evidence of neonlasm or trauma r

None

Not applicable

None

None

Far distal peripheral nerve lesions

MRI or CT evidenee of neoplasm or trauma

Not applicable

Not applicable

None

None

* With cross-references to chapters on neuroimaging, electrodiagnostics, tissue analyses, neuropsychology testing, and other tests. MRI, magnetic resonance imaging: CT, computed tomography; EEG, electroencephalogram.

and cricothyroid laryngeal muscles. y Evidence of denervation restricted to the cricothyroid or thyroarytenoid muscle alone indicates neuropathy of the superior laryngeal or recurrent laryngeal nerves, respectively. Denervation of both muscles places the lesion proximally in the laryngeal nerve or the vagus. Laryngeal EMG has also been useful in discriminating laryngeal dystonia (spasmodic dysphonia) from voice tremor and other disorders producing speech problems. y

Fluid and Tissue Analysis. Occasionally, biopsy of tissue outside the CNS may be productive in establishing a diagnosis involving the ninth and tenth cranial nerves. Amyloid neuropathy involving the cranial nerves may be demonstrated on peripheral nerve biopsy. Sarcoidosis with basilar meningitis and cranial neuropathies may be evident on lung or lymph node biopsy.

Cerebral Spinal Fluid and Intracranial Pressure. Lumbar puncture should be accomplished in cases of suspected CNS infectious or inflammatory disorders.

Neuropsychological Testing. Patients with pseudobulbar palsy may have findings of cognitive impairment on formal neuropsychological testing.

Other Tests. Patients with voice disorders should undergo careful otolaryngological evaluation of the neck and pharynx, and visualization of the vocal cords by either indirect or direct laryngoscopy. Paresis of the left vocal cord may result from disease processes in the chest involving the recurrent laryngeal nerve, such as an expanding aortic aneurysm, mediastinal adenopathy, or lung neoplasm. Chest radiographs, and possibly CT, should be employed to evaluate patients with suspected thoracic disease. Intravenous administration of edrophonium (Tensilon test) may be helpful in diagnosis of suspected myasthenia gravis.

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