Clinical Features

The multiplicity of MS plaques and their locations at various anatomic sites account for the great variability of clinical symptoms and signs (Table 8.2). Visual impairment, varying from diminished visual acuity to total blindness in one or both eyes, orbital pain, and frontal headaches are often the presenting symptoms. However, any cerebral or spinal cord dysfunction may introduce the disease.

Among diagnostic tests, magnetic resonance imaging (MRI) is particularly valuable in supporting the diagnosis (Figs. 8.10-8.12). It shows the typical periventricular plaques and also plaques as small as 3 to 4 mm. Using contrast material, MRI identifies acute plaques and is helpful in monitoring therapeutic efficacy. MS plaques are hypointense (black holes) on T1-weighted images and hyperintense on T2-weighted images. Proton-density images better delineate the periventricular lesions,

TABLE 8.2.

Multiple Sclerosis: Common Symptoms and Signs

Ocular

Somatosensory

Optic/retrobulbar neuritis

Paresthesias, dysesthesias,

Scotomas

sensory deficits,

Temporal pallor of optic

pain, Lhermitte's sign

disc

Autonomic/endocrine

Diplopia

Bladder, bowel, sexual,

Internuclear ophthalmoplegia

cardiovascular,

Nystagmus

temperature, eating,

Cranial nerves

sleeping disorders

Facial numbness

Speech/language

Facial palsy

impairment

Trigeminal neuralgia

Cognitive decline

Vertigo

Psychiatric

Motor

Behavioral changes

Weakness,

Euphoria

Ataxia

Depression

Tremor

Fatigue

Spasticity

Reflex changes

Pathologic reflexes

FIGURE 8.1 1

MRI of chronic MS plaques. Chronic lesions examined in axial planes. A. T1-weighted image shows extensive confluent hypointense lesions (black holes) in centrum semiovale. B. Parasagittal image shows lesions perpendicular to the ventricular surface (Dawson's fingers). C. On T2-weighted image, the lesions are hyperintense and the peri-ventricular lesions are indistinct from the CSF. D. On proton density (PD) images, the hyperintense periventricu-lar and small white matter lesions are distinct.

because the CSF is darker here than on T2-weighted images. The plaques are often oriented perpendicularly to the ventricular surface (Dawson's fingers). Magnetic resonance spectroscopy (MRS) is useful in demonstrating axonal injury. By measuring the concentration of N-acetyl aspartate (NAA), a neuron-specific marker, MRS monitors axonal dysfunction, which correlates with clinical disability. NAA levels are decreased in acute and chronic plaques. A temporary decrease in acute plaques is associated with reversible neurologic deficits. An increase in choline, a cellular membrane marker, indicates myelin breakdown.

Visual, somatosensory, and brainstem evoked potentials demonstrate a delay or a block in the conduction of nervous impulses and detect clinically silent plaques. CSF abnormalities are not specific, but an increase in y-globulin fraction and the presence of oligoclonal IgG bands further support the diagnosis. An acute solitary plaque, by producing edema with mass effect, may mimic a space-occupying lesion requiring a diagnostic brain biopsy. The definite diagnosis of MS is based on (a) two or more episodes of neurologic deficits separated in time by at least 1 month, (b) two or more noncontiguous anatomic lesions on MRI, and (c) the absence of an alternative clinical diagnosis.

Although the course of MS is not predictable, two major forms are distinguished: remitting-relapsing and progressiveā€”either from the onset (primary) or after a remitting-relapsing course (secondary). The outcome of an attack is defined by the anatomic and functional relationships between the myelin sheath and its axon, and between the myelin and the myelin-forming oligo-dendroglia. The severity and extent of axonal injury largely determines the degree of recovery or the persistence of neurologic deficits. Briefly, after the inflammation has resolved and the myelin debris has been removed, the conduction of the neural impulses is reestablished in the denuded nerve fibers. This results in remission with full or partial recovery of neurologic deficits. If remyelina-tion of nerve fibers occurs, this also contributes to remission. New plaques, which may develop at any time throughout the course of the disease, account for relapses. New attacks of myelin destruction, with a

FIGURE 8.12

MRI of MS plaques in the spinal cord. Multiple small hyper-intense lesions are present in several segments.

FIGURE 8.12

MRI of MS plaques in the spinal cord. Multiple small hyper-intense lesions are present in several segments.

further reduction in nerve fibers within and around an established plaque (active chronic plaque) account for the progression of existing neurologic deficits. The disability becomes permanent when the structural continuity of the nerve fibers is disrupted and wallerian degeneration develops.

The average duration of the disease is 25 to 30 years. Approximately one-third of patients have a benign course, with little disability for 15 years. Death is usually due to an intercurrent infection.

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