128 - pseudotumor cerebri

Signs and Symptoms

Pseudotumor cerebri (PTC) is encountered most frequently in young, overweight women between the ages of 20 and 45. Headache is the most common presenting complaint, occurring in more than 90 percent of cases. Dizziness, nausea, and vomiting may also be encountered, but typically there are no alterations of consciousness or higher cognitive function. Tinnitus, or a "rushing" sound in the ears, is another frequent complaint. Visual symptoms are present in up to 70 percent of all patients with PTC, and include transient visual obscurations, general blurriness, and intermittent horizontal diplopia. These symptoms tend to worsen in association with Valsalva maneuvers and changes in posture. Reports of ocular pain, particularly with extreme eye movements, have also been noted.

Funduscopic evaluation of patients with PTC demonstrates bilaterally swollen, edematous optic nerves consistent with true papilledema. Ophthalmoscopy may reveal striations within the nerve fiber layer, blurring of the superior and inferior margins of the neural rim, disc hyperemia, and capillary dilatation. More severe presentations involve engorged and tortuous retinal venules, peripapillary hemorrhages and/or cotton wool spots, and circumferential retinal microfolds (Paton’s lines). Chronic papilledema mayresult in atrophy of the nerve head, with associated pallor and gliosis. Most cases of true papilledema will not present with a relative afferent pupillary defect, although visual field deficits may be present. The most common visual field defect associated with PTC is an enlarged blind spot, followed by a nasal deficit, typically affecting the inferior quadrants. Other field losses seen in PTC include arcuate defects, nasal step, generalized constriction, and least commonly, cecocentral scotoma.

Pathophysiology
Pseudotumor cerebri is a syndrome disorder defined clinically by four criteria: (1) elevated intracranial pressure as demonstrated by lumbar puncture; (2) normal cerebral anatomy, as demonstrated by neuroradiographic evaluation; (3) normal cerebrospinal fluid composition; and (4) signs and symptoms of increased intracranial pressure, including papilledema.

While the mechanism of PTC is not fully understood, most experts agree that the disorder results from poor absorption of cerebrospinal fluid by the meninges surrounding the brain and spinal cord. The subsequent increase in extracerebral fluid volume leads to elevated intracranial pressure. However, because the process is slow and insidious, there is ample time for the ventricular system to compensate and this explains why there is no dilation of the cerebral ventricles in PTC. Increased intracranial pressure induces stress on the peripheral aspects of the brain, including the cranial nerves. Stagnation of axoplasmic flow in the optic nerve (CN II) results in papilledema and transient visual obscurations; when the abducens nerve (CN VI) is involved, the result is intermittent nerve palsy and diplopia.

Many conditions and factors have been proposed as causative agents of PTC, including excessive dosages of some exogenously administered medications (e.g., vitamin A, tetracycline, minocycline, naladixic acid, corticosteroids), endocrinologic abnormalities, anemias, blood dyscrasias, and chronic respiratory insufficiency. However the majority of cases remain idiopathic in nature.

Management
All patients presenting with suspected papilledema or other manifestations of intracranial hypertension warrant prompt medical evaluation and neurologic testing. Current protocol dictates that patients presumptively diagnosed with papilledema must undergo neuroimaging via computed tomography or, preferably, magnetic resonance imaging within 24 hours. These tests are meant to rule out space-occupying intracranial mass lesions, and therefore should be ordered with contrast media unless otherwise contraindicated. In cases of PTC, neuroimaging typically displays small to normal-sized cerebral ventricles with otherwise normal brain structure. Patients with unremarkable radiographic studies should be subsequently referred for neurosurgical consultation and lumbar puncture. (Lumbar puncture should not be ordered until neuroimaging is found negative for space-occupying mass due to risk for herniation of brainstem through foramen magnum secondary to mass during lumbar puncture.) Additional medical testing includes serologic and hematologic studies.

Therapy for patients with PTC varies, but in most instances initiate systemic medications as a first line treatment. Typically, the drug of choice for the initial management of PTC is oral acetazolamide (Diamox), although other diuretics including chlorthalidone (Hygroton) and furosemide (Lasix) may also be used effectively. Corticosteroid therapy is considered controversial in the management of PTC. While a short-term course of oral or intravenous dexamethasone may be helpful in initially lowering intracranial pressure, it is not considered to be an effective long-term therapy because of the potential for systemic and ocular complications.

For patients in whom conventional medical therapy fails to alleviate the symptoms and prevent pathologic decline, surgical intervention is the only definitive treatment. Cerebrospinal fluid shunting procedures are commonly employed in recalcitrant cases of PTC, but are successful in only 70 to 80 percent of cases. Optic nerve sheath decompression has also been advocated as a method to alleviate chronic disc edema, although this technique fails to directly address the issue of elevated intracranial pressure. It also demonstrates a particularly high failure rate.

Optometric management of patients diagnosed with PTC includes careful and frequent evaluation, including threshold visual fields, acuity measurement, contrast sensitivity, and indirect ophthalmoscopy. Photodocu-mentation of the nerve heads should also be performed.

Clinical Pearls

· PTC is a diagnosis of exclusion.

· Past literature refers to PTC as benign idiopathic intracranial hypertension, however this condition is far from benign. Patients may suffer intractable headache, severe nausea, intermittent diplopia and permanent vision loss, if they are not properly managed.

· Although no single causative agent has been identified, it is clear that one very common factor in patients with PTC appears to be obesity in women of childbearing age. Interestingly, significant weight loss in conjunction with conventional therapy leads to complete remission of this disorder in many instances.

· Patients with PTC should be enrolled in a formal weight-reduction program as a therapeutic measure.

· While PTC occurs most commonly in females of childbearing age, a number of cases have been encountered in male children.