| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SR) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we're going to be talking about posterior ischemic optic neuropathy. And the critical piece of course is the P, posterior. So as opposed to anterior ischemic optic neuropathy, where you have the disc edema that's visual during the acute phase. In posterior ischemic optic neuropathy, the P means that it is a retro bulbar optic neuropathy; and what that means is, there's no swelling. This is a very dangerous diagnosis to make, because there's so many things that could cause a retro bulbar optic neuropathy that have nothing to do with ischemia. And so, before we make a diagnosis of a retro bulbar PION, we want to have clinical confirmation that there is an RAPD. We want to make sure that we have a visual field defect that is corresponding with a nerve fiber layer loss. Or we might have central loss with central acuity and a central scotoma. And the disc has to be normal initially, in PION, but over time, the nerve will turn pale. So, in some respects, it's a retrospective diagnosis, because we have to see the optic atrophy develop in this patient after resolution of the retro bulbar optic neuropathy. And so, there are different types just like non-arteritic anterior ischemic optic neuropathy. There is non-arteritic PION, just like non-arteritic AION. And then there's arteritic PION. And then there are things that look like PION, but are really a retro bulbar optic neuropathy: either retro bulbar optic neuritis or compressive optic neuropathy. So, far and away, in an elderly patient, you should be thinking about arteritic PION. So, non-arteritic PION does occur. Usually it occurs in the setting of surgical procedures like spine surgery or cardiac surgery. They wake up with loss of vision and RAPD, field defect, loss of acuity, but a normal nerve and then it turns pale. In giant cell arteritis, same thing. Elderly patient, acute unilateral loss of vision, RAPD, normal fundus. And a fluorescein angiogram, fundus fluorescein angiogram, might be helpful in that setting to look for choroidal perfusion deficits in patients who has PION, because the other retro bulbar forms of optic neuropathy, like optic neuritis, MOG, NMO, or compressive lesions would not be expected to have a fluorescein angiogram showing choroidal perfusion deficit. Second thing is that you have to do an MRI scan of the head and orbit with gadolinium with contrast and fat suppression, because what we're looking for is enhancement of the optic nerve. And so, if we see enhancement of the optic nerve, then probably, you should not be considering PION. That usually means it is an inflammatory optic neuropathy. And then the young person that's MS, but in an older person, it could still be GCA, but that is when you have to really think, maybe I am dealing with one of the other optic neuropathies that are antibody mediated. MOG (myelinoligodendrocitic glycoprotein) or NMO (neuromyelitis optica). So the key differentiating radiologic feature is enhancement of the optic nerve. And you should be thinking about MOG and NMO. It is especially true if the patient has other autoimmune disease already, like lupus. That means we should really think about antibody mediated and not delayed type hypersensitivity granulomatous causes for the optic neuropathy. So, in summary, a posterior ischemic optic neuropathy is a retro bulbar optic neuropathy. It's characterized clinically by acute unilateral or bilateral loss of vision, visual field and neurofiber layer defect, RAPD if it is bilateral or asymmetric, and a normal nerve that becomes pale over time. It can be arteritic or non-arteritic. Should be thinking about giant cell. And I would do a fluorescein for choroidal perfusion deficit. Need to do an MRI scan and make sure it's not some other retrobulbar optic neuropathy. And you should be thinking about MOG and NMO in patients who have enhancing optic nerve, even if they are elderly patients. And if they are young patients, regular optic neuritis, MS, MS mimics, and of course NMO and MOG also still on the differential. And if everything is negative, then you can make the diagnosis of non-arteritic PION. But that usually occurs after surgical procedures. Spine or cardiac surgery. And I would recommend that the general ophthalmologist not make the diagnosis by themselves of non-arteritic PION. |
