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In virtually every patient who presents with overt or subtle manifestations of trigeminal nerve dysfunction, some form of laboratory evaluation is indicated ( Table 10-2

). Careful and directed neurological examination dictates the most important tests to obtain.

Neuroimaging. Once a lesion has been reasonably localized to the cortex, white matter pathways, thalamus, or brain stem, neuroimaging is essential to support a definitive clinical diagnosis (for complete text, see reference 'i/ ). Although computed tomography (CT) scanning can provide useful information regarding bony change or intracranial hemorrhage, magnetic resonance imaging (MRI) renders

TABLE 10-2 -- USEFUL STUDIES IN THE EVALUATION OF THE TRIGEMINAL NERVE

Syndrome

Neuroimaging

Eleetrophysiology

Fluid and Tissue Analysis

Neuropsychological Tests

Supranuclear

MRI with gadolinium for stroke, tumor, MS

EEG focal slowing or sharp waves

Increased protein, mild pleocytosis

Acalculia neglect

Nuclear lesions

MRI with gadolinium for stroke, tumor, MS

Abnormal BAEP, slowed blink reflex (V1)

Increased or normal protein, pleocytosis

NA

Preganglionic C-P angle

MRI with gadolinium for stroke, tumor, MS, meningitis, brain stem compression

Slowed blink reflex (V1)

Increased protein, pleocytosis, decreased glucose, abnormal cytology, positive CSF culture

NA

Gasserian ganglion

MRI with gradolinium for infection, tumor

Slowed blink reflex (V1)

Increased or normal protein, abnormal cytology, positive CSF culture

NA

Cavernous sinus

MRI with gadolinium for infection, thrombosis, aneurysm

Slowed blink reflex (V1)

CSF pleocytosis, low CSF glucose

NA

Peripheral CN V branches

Neuropathies

Slowed blink reflex (V1)

Increased or normal protein

NA

Trigeminal neuralgia

CN V root compression on MRI

No change

No change

NA

C-P, Cerebellopontine; MRI, magnetic resonance imaging; BAEP, brain stem auditory evoked potentials; NA, not applicable.

C-P, Cerebellopontine; MRI, magnetic resonance imaging; BAEP, brain stem auditory evoked potentials; NA, not applicable.

high-resolution models of regions not readily visible by CT such as the brain stem. In addition, subtle abnormalities such as early multiple sclerosis plaques, small tumors, or infarcts can often be visualized with gadolinium-enhanced MR images. MRI with gadolinium is a very useful way to visualize Meckel's cave [ial and to detect enhancement within the trigeminal nerve roots or gasserian ganglion. MRI with fine sections through the orbits is useful in assessing an orbital mass lesion and pain referable to V1. Orbital CT may also be useful. mR angiography and CT may be utilized to identify compression of the trigeminal nerve by the superior cerebellar artery. CT is the method of choice to evaluate the petrous apex especially in disorders such as Gradenigo's syndrome.

Electrophysiology. Electroencephalography (EEG) may reveal focal slowing or epileptiform abnormalities such as sharp waves or spikes in patients with significant cortical or hemispheric lesions. Because tumors, infarctions, and hemorrhages may also cause seizures in addition to sensorimotor trigeminal dysfunction, EEG may be very useful. In addition, if symptoms described are paroxysmal or intermittent, focal seizures must be considered in the differential diagnosis. Brain stem auditory evoked potentials (BAEPs) may be useful in assessing the possibility of an intrinsic brain stem process as well as lesions within the adjacent cerebellopontine angle. For example, BAEPs may assist in identifying people with occult multiple sclerosis or small vessel brain stem strokes that may have subclinically affected pontine or medullary regions in adjacent to the trigeminal nuclei.

Electrophysiological assessment of the corneal (blink) reflex latency can be reliably measured in an attempt to further localize a supranuclear, nuclear, or peripheral nerve processed This electrically elicited response is similar to that tested at the bedside, and it allows measurement of the response latency after stimulating either the afferent trigeminal or efferent facial nerve components. The facial nerve can be stimulated directly at its exit near the mastoids and the direct response latency (contraction of the ipsilateral orbicularis oculi muscles) measured. For normal adults, this value is typically between 3.0 and 5.0 msec. In contrast, the afferent and efferent limbs of the blink reflex can be tested by stimulating the supraorbital nerve or tapping the glabellar regions and measuring response time to bilateral orbicularis contraction (normal values, approximately 30 msec; ipsilateral and contralateral latency differences less than 5 msec). Prolongation of the blink latency may be seen in compressive lesions of the trigeminal nerve, acoustic neuroma, Guillain-Barre syndrome, hereditary motor and sensory neuropathy type I, diabetes, and intrinsic brain stem processes. In contrast, clinical utility of trigeminal somatosensory evoked potentials is limited by technical problems of reliability and reproducibility.

Fluid and Tissue Analysis. Laboratory studies may reveal evidence of vasculopathies like systemic lupus erythematosus or Sjoren's syndrome. White blood count elevations may suggest infections, and eosinophilia may indicate fungal disease. Altered glucose tolerance is seen with diabetes mellitus. Vitamin levels may indicate deficiencies of thiamine, folate, B12 , pyridoxine, or vitamin A.

Cerebrospinal Fluid Evaluation. If infectious, neoplastic (especially meningeal carcinomatosis), or inflammatory (sarcoidosis) etiologies are suspected, cerebrospinal fluid (CSF) evaluation is warranted. CSF glucose level, protein level, differential white and red blood cell counts, and cytology tests are compulsory, whereas other studies to isolate mycobacterial, fungal, rickettsial, parasitic, and viral pathogens should be addressed on an individual basis. In the immunocompromised person (e.g., one with cancer, acquired immunodeficiency syndrome [AIDS], and organ transplant), opportunistic pathogens causing infections such as cryptococcosis, candidiasis, mucormycosis, toxoplasmosis, and cytomegalovirus need to be seriously considered in the setting of any acute or subacute neurological presentation.

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Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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