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Man reports slowly decreasing vision in left eye
There was diffuse loss of peripapillary nerve fiber layer in the left eye and temporal nerve fiber layer thinning in the right eye.
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 Jeffrey Chang |  Vivek Chaturvedi | ||
A 46-year-old white man had decreased central vision in his left eye. He reported that the visual loss had been slowly progressive for about 18 months. He had been to his cornea specialist several times during this period for follow-up of his keratoconus.
At his most recent visit, the loss in central visual acuity was noted to be quite severe, as the patient could only be refracted to 20/200 in the left eye, whereas his best corrected visual acuity had been 20/40 just 1.5 years ago. The cornea specialist believed that the degree of visual deficit could not be explained by the patient’s anterior segment examination or corneal topography. The patient was therefore referred to a retina specialist for further evaluation.
The patient’s ocular history was significant only for keratoconus. He had undergone corneal transplantation in the right eye in 1996; he wore hard contact lenses in both eyes. His only medical problems were dyslipidemia, hypertension and gastroesophageal reflux disease. His medications included gemfibrozil, lisinopril and pantoprazole. He had no significant family history of ocular problems. He worked in real estate, and denied smoking, drinking or drug use.
Examination
On examination, the patient’s BCVA was 20/25 in the right eye and 20/200 in the left eye. Pupils showed no relative afferent pupillary defect. Confrontational visual field testing was suggestive of a superior temporal visual field defect in the right eye; vision was too poor in the left eye to assess for visual field deficit. Color vision was significantly diminished in the right eye, as the patient missed four out of eight color plates; central visual acuity was again too poor in the left eye to adequately evaluate color vision.
Anterior segment examination showed a clear corneal graft as well as a hard contact lens in the right eye and trace nuclear sclerotic cataract in both eyes. Fundus examination revealed mild optic disc pallor in both eyes, more prominent in the left eye than in the right (Figure 1). The retina was unremarkable. OCT nerve fiber layer imaging revealed diffuse loss of peripapillary nerve fiber layer in the left eye and temporal nerve fiber layer thinning in the right eye.
 Mild optic disc pallor was prominent in the left eye. |
What is your diagnosis?
Progressive visual loss
The differential diagnosis for progressive bilateral nerve fiber loss causing optic disc pallor is extensive. The various causes can be divided into several broad categories, including compressive, hereditary and infiltrative causes, in addition to conditions related to toxin or drug exposure, as well as nutritional deficiencies.
Among these categories, a compressive optic neuropathy should be strongly considered in this middle-aged man presenting with a slow progressive visual loss and field deficit. Compression of the optic chiasm, with or without extension to the optic nerves, is a common cause of bilateral asymmetric optic neuropathy. The most frequently encountered lesions in this category include pituitary adenomas, craniopharyngiomas, meningiomas, gliomas, as well as internal carotid artery aneurysms impinging on the optic chiasm. A compressive optic neuropathy can also be caused by thyroid ophthalmopathy, via enlargement of the extraocular muscles and surrounding tissues.
The most common hereditary cause of bilateral optic neuropathy in men of this age group is Leber’s hereditary optic neuropathy. This condition displays mitochondrial inheritance and causes a severe monocular visual loss occurring over a few weeks or months, associated with a relative afferent pupillary defect and a central or centrocecal visual field deficit. Involvement of the second eye usually presents itself within a couple of months. Given the protracted time course of visual loss, Leber’s would be less likely in this patient.
There are multiple toxin-, nutrition- and drug-related optic neuropathies. Tobacco-EtOH amblyopia is well-known but infrequently encountered. Low B12 and low folate levels can also cause nerve fiber layer loss. Multiple drugs, such as ethambutol, INH and chloroquine, are believed to cause optic neuropathy.
Numerous infiltrative processes can present with progressive visual loss due to optic nerve infiltration. These include neoplastic conditions, especially leukemia and lymphoma; however, these are rare causes. Granulomatous processes, such as tuberculosis, sarcoid, syphilis and fungal infections, can also infiltrate the optic nerves. The lack of inflammation on examination makes these diagnoses less likely in this patient.
Diagnosis
The patient had a history of fatigue and headache for several months. Humphrey visual field testing showed a right homonymous hemianopia. Based on these findings, tumor was the most likely diagnosis. The patient’s MRI revealed a 6 cm by 8 cm mass arising from the sella, severely compressing the left optic nerve and partially compressing the optic chiasm and the right optic nerve (Figure 2). The mass extended to the posterior cranial fossa and impinged on the left optic tract. Based on its radiologic appearance, the mass was suspected to be a pituitary adenoma. A prolactin level was found to be markedly elevated at 33,000 ng/mL, consistent with a prolactin-secreting pituitary adenoma.
 MRI revealed a mass arising from the sella, compressing the left optic nerve. |
Discussion
Prolactin-secreting pituitary adenomas account for 40% of all pituitary adenomas. They present early in women, with symptoms of galactorrhea and amenorrhea. Men have more vague symptoms, such as fatigue and progressive loss of libido, and so the tumors present later and at a larger size. Men are therefore more likely to have neurological and visual deficits at time of presentation due to the larger tumor size.
Diagnosis is made via radiologic imaging, as well as laboratory tests confirming elevated levels of the hormone. The rise in serum prolactin levels parallels tumor growth and can be used to monitor progression of the lesion. Prolactin secretion is mediated by the neurotransmitter dopamine. Initial treatment of prolactinoma therefore involves administration of dopamine agonists, such as bromocriptine and cabergoline. Cabergoline has been found in several studies to be a more effective inhibitor of prolactin than bromocriptine, with a better side effect profile.
Once treatment with a dopamine agonist is initiated, patients should undergo repeat visual field testing 1 month after starting therapy. A repeat MRI should be performed after 6 months of treatment, and prolactin levels should be checked yearly.
Follow-up
The patient was evaluated by a neuroendocrine specialist and was started on cabergoline, a dopamine agonist. A follow-up visual field study done several weeks later showed marked improvement in the field defect. The patient also noted that his visual acuity seemed improved. A follow-up MRI in a few months is planned.
References:
- Arafah BM, Nasrallah MP. Pituitary tumors: pathophysiology, clinical manifestations and management. Endocr Relat Cancer. 2001;8(4):287-305.
- Foroozan R. Chiasmal syndromes. Curr Opin Ophthalmol. 2003;14(6):325-331.
- Karavitaki N, Cudlip S, Adams CB, Wass JA. Craniopharyngiomas. Endocr Rev. 2006;27(4):371-397.
- Newman NJ. Hereditary optic neuropathies: from the mitochondria to the optic nerve. Am J Ophthalmol. 2005;140(3):517-523.
- Schiefer U, Isbert M, Mikolaschek E, et al. Distribution of scotoma pattern related to chiasmal lesions with special reference to anterior junction syndrome. Graefes Arch Clin Exp Ophthalmol. 2004;242(6):468-477.
- Schlechte JA. Clinical practice. Prolactinoma. N Engl J Med. 2003;349(21):2035-2041.
- Priti Batta, MD, and Thomas R. Hedges III, MD, can be reached at Tufts Medical Center, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; Web site: www.neec.com.
- Edited by Jeffrey Chang, MD, and Vivek Chaturvedi, MD. Drs. Chang and Chaturvedi can be reached at New England Eye Center, Tufts University School of Medicine, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; Web site: www.neec.com.
