Bilateral Optic Disc Edema
Optic disc edema refers to the ophthalmoscopic swelling of the optic disc with a concurrent increase in fluid within or surrounding the axons. While unilateral disc edema is more common, bilateral disc edema can occur. Many terms have been used to describe optic disc edema including swollen optic disc, disc edema, papilledema, papillitis, choked disc, and elevated optic nerve. The broadest terms to describe this phenomenon are optic disc edema and swollen optic disc, whereas the other terms imply the cause of the optic disc swelling. For example, papilledema implies optic disc edema due to increased intracranial pressure (ICP). For this reason, this article will use both optic disc edema and optic disc swelling interchangeably.
When discussing bilateral optic disc edema as opposed to unilateral optic disc edema, the most likely etiological categories are increased intracranial pressure (ICP), infectious/inflammatory, toxic-metabolic/nutritional, and hypertensive emergency (ie, malignant hypertension). Optic disc edema (ie, papilledema) due to increased ICP can be caused by many disease processes including intracranial space occupying lesions, CSF producing tumors, obstructions of the arachnoid villi, and idiopathic intracranial hypertension (IIH). Infections and inflammatory conditions can result in bilateral disc edema either from direct infiltration or inflammatory effects or secondary to increased intracranial pressure. Lyme disease, cat scratch disease, and syphilis can all directly cause bilateral optic disc swelling due to infiltration whereas viruses can often precede optic neuritis. Toxic causes of bilateral optic disc edema are numerous and can include drugs such as antimicrobials, immunomodulators, chemotherapeutic agents, etc. along with many others chemicals not used for medical treatments.Hereditary and mitochondrial disorders will often result in bilateral involvement. Although less common, causes of unilateral optic disc edema such as optic neuritis, ischemia, and compression can occur bilaterally.
The risk factors vary with the etiology. Infectious and toxic causes depend upon exposure to the causative agent. Papilledema risk factors include those for pseudotumor cerebri such as obesity, female sex, and use of certain medications. Uncontrolled hypertension increases the risk of disc edema. A history of cerebrospinal fluid shunt device places a person at risk due to a high rate of shunt malfunction over time and optic disc edema may be the presenting or only sign of shunt failure in these patients.
In general, optic disc swelling alone refers to axonal distension and elevation of the optic disc, and optic disc edema indicates optic disc swelling along with increased fluid surrounding the axons. This is caused by obstruction of slow and fast axoplasmic transport resulting in axoplasmic backflow.
A good history is key to creating a differential diagnosis. Review the medical history for recent headaches and/or weight gain, transient visual obscurations, pulsatile tinnitus, history of malignancy or autoimmune disease. Discuss with the patient not only current medications, but supplements, topical applications, and recently discontinued agents. When considering an infectious etiology, inquire about recent tick bites, rashes, upper respiratory viral symptoms, gastroenteritis symptoms, cat scratches or recently exposure to cats, and sexually transmitted diseases.
Vital signs should be obtained initially to screen for hypertensive emergency (ie, malignant hypertension) in all patients with bilateral optic disc edema. Visual acuity testing in optic disc edema may be normal (e.g., papilledema) or decreased (e.g., papillitis), and the visual field test can have variable results. For example, if the cause of the optic nerve edema is papilledema, then there can be peripheral nerve fiber layer related vision loss or an increase in the size of the blind spot; whereas, if the cause is an acute toxic or nutritional etiology then the most common visual field defects are central and cecocentral scotomas. When examining the pupils, in contrast to unilateral optic disc edema, there may or may not be a relative afferent pupillary defect (RAPD) if there is bilateral and symmetric disease. Fundoscopic exam in optic disc swelling will demonstrate various findings based on the severity and duration of the optic disc swelling but in general the appearance alone of the optic disc edema is not usually specific enough to make an etiologic diagnosis.
Initially, there may only be mild obscuration of the nerve fiber layer presenting clinically as blurring of the disc margin. Over time and with increasing grade (Frisen) and severity, hyperemia of the optic disc head develops due to dilated disc telangiectatic capillaries. As the disc swelling increases in severity one may find more obligatory signs of pathology such as hemorrhages in the peripapillary nerve fiber layer, hard exudates, subretinal fluid, and cotton wool spots. Chronically swollen optic discs may develop surface vessels that serve as collateral supply to carry blood away from the central retinal vein to the choroidal vortex veins (i.e., retinochoroidal venous collaterals). More severe or chronic disc swelling may have associated retinal striae or wrinkles or develop choroidal folds. Over time secondary atrophy and gliosis may make it difficult to differentiate the various etiologies of chronic optic disc edema.
The work up for optic disc edema should be individualized based upon the history and exam but in general neuroimaging is recommended for unexplained optic disc edema (especially bilateral). Typically, the preferred imaging study is an MRI of the brain and orbit with and without contrast and including fat suppression sequences. An MRV (Magnetic Resonance Venography) also is recommended in suspected papilledema cases to evaluate the dural venous sinuses for thrombosis. In addition, if the MRI is negative, a lumbar puncture may be needed to assess for elevated opening pressure and signs infection or inflammation (e.g., CSF cell count, protein, glucose). If toxic or infectious etiologies are suspected, then other laboratory or serologic testing may be indicated. CT scan may be the initial imaging study in acute settings (eg, emergency room) or if there is a contraindication to MRI (eg, ferromagnetic material).
Disease management depends upon the etiology of the bilateral optic disc edema. The goal is to treat the underlying cause in order to reduce the disc edema as quickly as possible.
Medical therapy options will depend on the underlying etiology. For instance, malignant hypertension is typically managed in the inpatient setting with intravenous antihypertensive agents as an inpatient. Acetazolamide (and other diuretics) can be used to expedite resolution of disc edema for idiopathic intracranial hypertension but can be used in other causes of papilledema as indicated and may be contraindicated (eg, cryptococcal meningitis). Inflammatory etiologies may require corticosteroid or immunosuppressive therapy. Demyelinating disease (e.g., multiple sclerosis) may require high dose or intravenous corticosteroids or immunomodulatory therapy. Infectious etiologies may require directed antibiotic therapy. Acetazolamide may be contraindicated in cases of cryptococcal meningitis due to higher morbidity and mortality related to metabolic acidosis).
If an intracranial mass lesion is found, the patient may require neurosurgical intervention. Persistent disc edema due to increased ICP that does not respond to maximum medical therapy or that is associated with acute vision loss at onset (e.g., fulminant IIH) may require treatment surgically with optic nerve sheath fenestration and/or cerebrospinal fluid shunt device (e.g., ventriculoperitoneal shunt). A lumbar drain may be necessary for papilledema in the acute setting (eg, fulminant IIH) as a temporizing measure prior to definitive surgical treatment.
Optic disc edema that is left untreated can lead to permanent and irreversible blindness.
Prognosis depends upon the etiology and treatment of the bilateral optic disc edema. With appropriate and prompt treatment, in most cases vision can be preserved. As noted above however prolonged disc edema increases the risk of permanent nerve damage and vision loss. Patients presenting with acute and severe disease at onset (e.g., malignant hypertension or fulminant IIH) require more urgent and aggressive intervention for better long-term prognosis.
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