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Julie Vajnar, PA-C, RT, DEPARTMENT EDITOR

MRI confirms cause of facial numbness

Julie Vajnar, PA-C, RT

The author practices in a radiology group at North Oaks Health System, Hammond, La. She has indicated no relationships to disclose relating to the content of this article.

CASE

The patient is a 34-year-old black female who presents with intermittent right facial numbness. She has no other complaints. She states the numbness has been present “off and on” for 12 months. She has no pain or pruritus. She reports that she had an episode of weakness in her left leg several months ago but that it has since resolved.

On physical examination, her facial skin appears unremarkable. No carotid bruit is noted. There is decreased sensation on the right side of the face compared to the left. The results of testing for visual acuity and motor function are normal, as are laboratory results, including those on a CBC and a test to measure thyroid-stimulating hormone. You decide to order MRI of the brain (see Figure 1). What does the MRI reveal?

DISCUSSION

The image shows multiple small, bright, round and oval lesions in the frontal region with a larger, bright ovoid lesion in the left parietal lobe. This larger lesion is perpendicular to the lateral ventricle and located in the white matter of the brain. These findings are compatible with a demyelinating disease.

The differential diagnosis in a situation like this is vast and includes vasculitis, Lyme disease, multiple sclerosis, embolic disease, ischemia, migraine, and hypoxia. A thorough history, physical examination, and diagnostic studies are needed to narrow the differential and to reach a diagnosis. This patient also underwent a lumbar puncture, the results of which demonstrated oligoclonal antibody bands. At that point it was determined she had multiple sclerosis (MS).

MRI is useful in evaluating patients with suspected MS. Alone, it is not diagnostic, but MRI has been shown to demonstrate lesions of the brain and/or spinal cord in approximately 90% of clinically confirmed cases of MS, whereas CT demonstrates lesions in only about 50% of confirmed cases (see Figure 2).

Many sequences are performed during an MRI of the brain, but the most helpful is the FLAIR sequence, which is seen in Figure 1. FLAIR stands for fluid-attenuated inversion recovery. It is an MRI sequence that suppresses CSF, making lesions in the periventricular space more obvious, and is best for demonstrating supratentorial white matter disease. The MRI results suggestive of MS include high signal intensity (brightness) on T2-weighted and FLAIR sequences, location of lesions abutting the ventricles (usually perpendicularly), multiplicity of lesions, location of lesions at or near the gray-white matter junction, and ovoid or round lesion shape. The lesions may also be noted in the spinal cord, the cerebellar and cerebral peduncles, and the corpus callosum; if they are present in these locations, the likelihood of MS is increased, as these areas are usually not involved in ischemia.

Multiple sclerosis is a chronic neurologic disease that results in inflammation and myelin damage in the CNS. Diagnosing MS is difficult since it can mimic many other conditions. Two or more lesions in the brain or spinal cord should be present on imaging for diagnosis, and some or all of the lesions should be seen in different locations in the CNS on subsequent examination.

Patients with MS are usually 20 to 50 years old at onset, and women are more likely than men to be affected. Signs and symptoms may include dizziness, fatigue, urinary bladder dysfunction, numbness or tingling, weakness, or monocular visual impairment, although the patient may present with any neurologic deficit. The disease may have unpredictable relapses and remissions. Other causes of the symptoms—including CNS infection, inflammatory processes, vascular disease, anatomic or compressive disorders of the brain or spinal cord, and genetic disorders—must be excluded.

Lumbar puncture is usually performed if MS is suspected. Oligoclonal antibody bands may be present on an isoelectric focusing assay, but this alone also does not confirm the diagnosis. The CSF is also evaluated for the IgG index because in MS, the CSF IgG concentration is usually increased relative to other CNS proteins. Lumbar puncture can help exclude neoplasm or infection as well. Oligoclonal bands and the IgG index are abnormal in approximately 90% of patients who have MS.

Evoked potential testing is also used to provide objective evidence of lesions that may be suspected based on the patient’s subjective complaints. Electrodes are placed on the head and body during this procedure, and an electrical stimulus is delivered. The response to the stimulus is recorded to determine any delay in nerve transmission.

Early diagnosis is important in MS. Although no cure is available, evidence exists that early treatment can delay disability and slow down injury to the CNS. When combined with a detailed history, neurologic examination, evoked potential testing, and lumbar puncture, MRI can increase the clinician’s confidence that a diagnosis of MS is correct.