Sunday, November 13, 2011

Demyelinating Optic Neuropathy (Optic Neuritis, Retrobulbar Optic Neuritis)

Signs and Symptoms
Optic neuritis (ON) is defined as acute inflammation of the optic nerve. While etiologies include infection (syphilis, mumps, measles), infiltrative/ inflammatory disease (sarcoidosis, lupus), ischemic vascular disease (diabetes), the most common etiology is the demyelinating disease multiple sclerosis (MS). ON is the initial presenting sign in 20 to 25 percent of MS patients. Anywhere from 35 percent to 75 percent of patients who present with ON develop clinical MS. The risk of developing MS increases steadily during the first 10 years after the initial presentation of ON. The usual age range for the diagnosis of MS is 15 to 45 years. While some sources cite a predilection for females, the topic of sexual distribution remains controversial.

The clinical presentation of demyelinating optic neuropathy varies. Patients frequently present to the office with an acute loss of vision. The natural history of MS-related vision loss is rapidly progressive acuity loss for a period of 10 days, which then stabilizes and improves. Additional ocular signs include eye pain, tenderness of the globe, dyschromatopsia, decreased brightness sense, decreased color perception, a relative afferent pupillary defect, assorted visual field defects (altitudinal and central/cecocentral), phosphenes upon eye movement and optic disc swelling with or without vitreous cells. Often, the optic nerve is normal in appearance and the dysfunction is considered retrobulbar.

Systemic signs and symptoms may include headache, nausea, Uhtoff’s sign (decreased vision with or without limb weakness following exposure to increased temperatures i.e., a bath or exercise), Romberg’s sign (patient falls when they close their eyes), Pulfrich’s stereo phenomenon (beer barrel appearance to the environment) and fever.

Multiple sclerosis is an acquired, multifactorial, inflammatory demyelinating disease, which affects the white matter located in the central nervous system. Myelin is responsible for speeding electrical impulses along nervous tissues. Loss of myelin greatly slows nervous conduction and leads to the neurologic deficits seen in MS.

Although the exact cause of MS is presently unknown, many theories regarding its etiology exist. The most common theories involve the immune system. The immune system attacks and destroys antigens by two different mechanisms. One mechanism, known as cellular immunity, involves a response by macrophages and T-cells. The other mechanism, governed by B-cells and antibodies is known as humoral immunity. Evidence suggests that the cellular immune response contributes to the loss of myelin. This patchy demyelination is thought to be caused by a deposition of mononuclear cells such as macrophages and B-cells in perivascular regions. Demyelinating optic neuropathy can damage the fibers in both the visual and pupillary pathways. This damage interrupts nerve impulses within the pathways, producing decreased vision as well as an afferent pupillary defect.

In the past, controversy existed as to whether or not to treat patients with ON with corticosteroids. The Optic Neuritis Treatment Trial (ONTT) supports the administration of intravenous methylprednisolone sodium succinate (Solumedrol, 250 mg. every 6 hours) for three days followed by oral prednisone (1 mg/kg per day) for 11 days for the purposes of accelerating visual recovery. This therapy did not improve visual outcome after one year but was found to increase the rate at which patients recover. The ONTT also determined that the use of oral prednisone (1 mg/kg per day) alone for 14 days is contraindicated. Patients receiving this therapy had a higher rate of new attacks of ON in both the initially affected and fellow eyes than did the intravenous/oral group and placebo group.

As recorded in the three-year follow-up of patients in the ONTT, treatment with intravenous methylprednisolone followed by oral corticosteroid regimens reduced the two-year rate of development of clinical MS, particularly in patients with signal abnormalities consistent with demyelination on MRI of the brain at the time of study entry. Serious side effects of glucocorticoid therapy are infrequent. Therefore, outpatient administration of high-dose intravenous glucocorticoids may be recommended.

Clinical Pearls

A number of other types of demyelinating disorders have been associated with ON. They are: acute transverse myelitis, Guillain-BarrĂ© syndrome, Devic’s neuromyelitis optica, Charcot-Marie-Tooth syndrome, multifocal demyelinating neuropathy, and acute disseminated encephalomyelitis.

Diseases such as syphilis, toxoplasmosis, histoplasmosis, tuberculosis, hepatitis, rubella, human immunodeficiency virus (HIV), Lyme borreliosis, familial Mediterranean fever, Epstein-Barr virus, herpes zoster ophthalmicus, paranasal sinus disorder, sarcoidosis, systemic lupus erythematosus, Bechet’s disease, and diabetes may cause optic neuropathy and should be considered before prematurely diagnosing demyelinating optic neuropathy.

In cases of optic neuropathy presumably secondary to demyelinating disease, MRI can assist in systemic diagnosis by identifying both old and acute demyelinating plaques within periventricular white matter.

Significant pain with eye movement is present in nearly every case of demyelinating optic neuropathy.

As the visual dysfunction is due to autoimmune destruction of myelin

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