Lenworth N. Johnson

Alteration of the visual evoked potential by macular holes: Comparison with optic neuritis

Nine patients with maculopathy (macular holes, macular cysts, and lamellar holes) and ten patients with optic neuritis were examined in order to determine changes in the visual evoked potential (VEP) in response to pattern-reversal stimulation. Eyes with lamellar holes had normal P100 latency, but eyes with macular cysts and macular holes had prolonged P100 latency. Eyes with optic neuritis exhibited greater prolongation of the P100 latency than eyes with macular holes. In contrast, eyes with macular holes had a greater reduction in the steady-state VEP amplitude than eyes with optic neuritis. The prolonged latency occurring in maculopathy may be due to a peculiar amplitude summation noted with half-field VEP, rather than to a true conduction delay like that seen in eyes with optic neuritis. The amplitude slope, which is usually positive in normal controls, was negative for 85.7% of eyes with macular holes and 69.2% of eyes with optic neuritis. The negative amplitude slope may represent a subtle defect in retinal ganglion X cells. Eyes with significantly lower values for four or more of the nine central test points on quantitative automated perimetry had negative amplitude slopes and prolonged P100 latency.

Magnetic resonance imaging of craniopharyngioma.

Craniopharyngiomas are common tumors located in the suprasellar region. Contrast enhancement, cyst formation, and calcification are the three characteristic features of craniopharyngiomas on computed tomographic scan. More than 90% of suprasellar craniopharyngiomas exhibit at least two of these three features, thus providing easy radiologic detection. We treated a 41-year-old man in whom a large suprasellar craniopharyngioma producing severe visual loss was not detected by computed tomography but was easily identified with magnetic resonance imaging. Thus, despite high-resolution computed tomographic scan, large suprasellar craniopharyngiomas can be missed. Magnetic resonance imaging may be superior to computed tomography in detecting these tumors.

Digoxin toxicity presenting with visual disturbance and trigeminal neuralgia.

We present a patient with monocular blindness and ipsilateral internal carotid artery dissection to complement those recently reported by Newman et al.1 Case report. An HIV-positive, drug-abusing woman presented to the New England Medical Center with blindness in the right eye, which she had noticed upon awakening that morning. She had had right-sided retrobulbar headache during the previous day and 6 monthsprior to admission had been appropriately treated for Staphylococcus aureus bacterial endocarditis. She recalled no previous visual symptoms. Examination revealed a 4/6 systolic ejection murmur. No bruits were heard in the neck or head. Vision was light perception in t h e r ight eye with a relative afferent pupillary defect. Ophthalmoscopic examination showed normal retinas without vascular abnormalities and healthy-appearing optic disks on both sides. Visual acuity and Goldmann visual field examinations of the left eye were normal. The rest of her neurologic examination was normal. Head and orbital CTs were normal. Right carotid angiography revealed a string sign2 suggestive of internal carotid artery dissection beginning 2 em above the bifurcation. The patient was heparinized until blood cultures grew Streptococcus viridans. Two days after heparin was discontinued, the patient developed a left hemiplegia af€ecting face, arm, and leg. Signs of retinal ischemia never appeared although by 6 weeks the optic disk had begun to develop pallor. An electroretinogram (ERG) showed normal scotopic function bilaterally, whereas visual evokedpotentials (VEPs) were absent on rightsided stimulation and normal on the left. Subsequent review of the patient’s medical history elucidated an episode of pulsatile hemorrhage from the right side of the neck while undergoing intravenous catheter placement during the previous hospitalization. Discussion. Internal carotid artery dissection with subsequent embolization to ipsilateral ophthalmic artery explains the blindness experienced by the patients reported by Newman et al.1 Our patient also suffered internal carotid artery dissection, probably due to previous injury, and subsequent ipsilateral monocular blindness. Yet, in contrast to the cases described by Newman et al,’ there were no signs of retinal or anterior optic nerve ischemia in our patient. These normal physical findings, the absent VEP with preserved ERG, and the normal visual field in the left eye indicate retrobulbar, prechiasmal optic nerve damage. The optic nerve head receives its blood supply from the central retinal artery (surface nerve-fiber layer) and the posterior ciliary arteries (laminar and prelaminar regions).3.4 Both these arteries are branches of the ophthalmic. Similarly, the intraorbital and intracanalicular portions of the optic nerve also derive most of their blood supply from the ophthalmic viapial capillary networks as well as from intraneural branches of the central retinal artery.5 The intracranial portion of the optic nerve, however, receives no blood supply from the ophthalmic and its branches; rather, its supply is derived from anterior cerebral and internal carotid artery perforators. Infarction of this portion of the optic nerve due to occlusion of its perforating arterioles would cause monocular blindness yet preserve the ophthalmic, retinal, and ciliary circulation. We think our patient provides another example of carotid artery dissection presenting as sudden monocular blindness, in this case due to a posterior ischemic optic neuropathy. The likely mechanism was occlusion of perforators to the intracranial portion of the optic nerve with preservation of the circulation subserving the anterior optic nerve and retina. The subsequent left hemiplegia presumably resulted from occlusion of the middle cerebral artery secondary to an artery-to-artery embolus originating from the region of the dissection. Had the patient not had bacterial endocarditis and had she been maintained on anticoagulants, hemiplegia may have been averted.2.6

Hemianopia respecting the vertical meridian and with foveal sparing from retinal degeneration

lumbosacral ganglia, which have only interganglia and postganglionic fibers. When sympathetic ganglia or postganglionic fibers along the lumbosacral plexus or the peripheral nerves are damaged below the segment L3, autonomic disturbances appear, which are not preeent with lesions of the nerve roots or cauda equina.l.2 However, clinically it is difficult to differentiate LSP from lesions of the spinal cord, cauda equina, or nerve mot. Our patient’s myelogram was normal, as were CSF studies. Additionally, epidural metastasis, usually below the conus medullaris, has been demonstrated in 45% of patients with neoplastic LSP by myelography.3 Furthermore, myelography might help delineate radiation porta because the epidural tumor may be at the fringe of or outside the conventional pelvic port. In cancer patients, along with the classic quintet of leg pain, weakness, edema, rectal mass, and hydronephrosis, which are strongly suggestive of neoplastic LSP? look for vegetative symptoms in the neurologic examination. The spontaneous onset of a warm and dry foot in a cancer patient is a valuable diagnostic clue to retroperitoneal metastasis. Furthermore, motor or sensory disturbances at lumbosacral segments indicate LSP. rather than a radiculopathy or cauda equina syndrome.lJ

Tetracycline delays ocular motility decline in chronic progressive external ophthalmoplegia

Chronic progressive external ophthalmoplegia (CPEO) is a mitochondrial cytopathy characterized by bilateral ptosis during adolescence, followed later by limitation of extraocular muscle movement and diplopia.1 The biochemical defect consists of mutations or deletions of mitochondrial DNA genes that encode respiratory chain enzymes involved in adenosine triphosphate (ATP) generation and its subsequent translocation from the mitochondria.1 To date, there is no definitive treatment that reverses or halts the progression of the muscle weakness. Herein, we report improvement in ocular motility in a patient with CPEO following treatment with tetracycline. The retrospective review was approved by the institutional review board. A 47-year-old woman, with bilateral upper eyelid ptosis since childhood, underwent ptosis repair in 1987, at age 28. There was a gradual return of the ptosis over the ensuing years. By age 33, she began experiencing diplopia. She had otherwise enjoyed excellent health. Her family history was significant for six brothers and three sisters with ptosis. We initially evaluated her in October 1997, at age 38, for diplopia and ptosis. Her visual acuity was 20/20 for both eyes. There was 6- to …

Primary aberrant regeneration of the oculomotor nerve from presumed extracavernous neurilemmoma, meningioma, and asymmetric mammillary body

Previous reports of primary aberrant regeneration have indicated that its presence is diagnostic or suggestive of intracavernous meningioma or aneurysm. Three cases of extracavernous processes (presumed oculomotor nerve neurilemmoma, meningioma, and asymmetric mammillary body) associated with primary aberrant regeneration are presented. Magnetic resonance imaging was helpful in identifying two processes not noted on computed tomographic scan. Computed tomography was helpful in further delineating the meningioma. The value of magnetic resonance imaging and computed tomographic scan in the evaluation of primary aberrant regeneration is indicated from these cases.

The 5-year risk of MS after optic neuritis

To the Editor: The ONTT has identified the presence of one or more brain MRI lesions at the time of optic neuritis as the single most important predictor of the development of CDMS at 5 years.1 The cumulative probability of CDMS at 5 years was 16% without brain MRI lesion, 37% for one to two MRI lesions, and 51% for three or more MRI lesions. Examination of the probability curves (figure 2 in reference 1), which combined the outcomes of the placebo (natural history), prednisone, and IV SoluMedrol groups, suggests a high rate of conversion to CDMS within the first year, followed by an apparent linear increase in MS conversion for patients with no, one to …