Severe Vision Loss and Intracranial Hypertension Presenting as Delayed Sequelae of "Mild" Carbon Monoxide Poisoning

A 32-year-old non-smoker man presented to neuro-ophthalmology service with progressively worsening bilateral vision loss for 3 weeks. His medical history was only significant for migraines; 4 weeks before presentation, he was admitted at an outside hospital after being found unconscious by his sister.

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Caroline Froment, MD, PhD An-Guor Wang, MD Severe Vision Loss and Intracranial Hypertension Presenting as Delayed Sequelae of “Mild” Carbon Monoxide Poisoning James H. Garcia, BS, Sangeeta Khanna, MD CASE REPORT A 32-year-old non-smoker man presented to neuroophthalmology service with progressively worsening bilateral vision loss for 3 weeks. His medical history was only significant for migraines; 4 weeks before presentation, he was admitted at an outside hospital after being found unconscious by his sister. His carbon monoxide (CO) levels were found to be elevated at the scene, and he was immediately started on normobaric oxygen by mask en route to the hospital. On arrival, the patient was awake with a normal neurological examination except for complaints of a headache. His carboxyhemoglobin levels (COHb) were reported to be 2.8% and classified as mild CO poisoning. On day 2 after admission, the patient experienced a seizure and was started on zonisamide 50 mg daily for seizures and naproxen for headaches. Noncontrast computed tomography (CT) head, CT neck, MRI brain, and electroencephalograms were all unremarkable, and after resolution of symptoms, he was discharged on day 3. He reported onset of mild blurring of vision in the right eye in the hospital and subsequent continued worsening of vision in both eyes with increasing pressure and pain behind the eyes and neck. He also endorsed a worsening headache different from his usual migraine headache, numbness, and paresthesias in his hands. On examination in the neuro-ophthalmology clinic 4 weeks after the incident, he was alert and oriented; he had count fingers vision in the right eye and hand motion vision in the left eye with dense central scotoma bilaterally and bilateral disc edema (Fig. 1). He reported severe headache and pain behind both eyes. He was admitted for urgent workup. MRI Orbit w/wo contrast did not show any enhancement of the optic nerves but did show flattening of the globes (Fig. 2A). MRI brain was normal without hydrocephalus or other abnormality. MR venogram showed narrowing of dural venous sinuses, most pronounced in transverse sinuses and parts of superior sagittal sinus (Fig. 2B). An urgent lumbar puncture was conducted, which revealed an opening pressure of 50 cm of H20. He was started on acetazolamide 2g twice a day, IV methylprednisolone, and neurosurgery was consulted for lumbar drain in view of drastically reduced vision with raised intracranial pressure (ICP). Because of concern for carbon monoxide toxic optic neuropathy, he was started on thiamine and folic acid. Toxicology was also consulted and recommended against hyperbaric oxygen at this time 4 weeks after exposure. Neurosurgery performed a right ventriculoperitoneal shunt, and the patient noted minimal improvement in vision and resolution of headaches. Five days after discharge, the patient’s ophthalmologic examination revealed visual acuity of 8/200 in the right eye and 2/300 in the left eye. A follow-up magnetic resonance venography revealed increased caliber of the dural venous sinuses, which now showed normal smooth outline (Fig. 2C). On follow-up, the patient’s vision continued to be stable, was headache free, and developed temporal optic atrophy as papilledema resolved. Vision loss was attributed to carbon monoxide toxic optic neuropathy with additional insult from severely elevated ICP. Carbon monoxide is an odorless gas which, when inhaled, can have devastating hypoxic consequences because CO has an Saint Louis University School of Medicine (JG, SK), St. Louis, Missouri; and Departments of Ophthalmology (SK) and Neurology (SK), Saint Louis University, St. Louis, Missouri. The authors report no conflicts of interest. Address correspondence to Sangeeta Khanna, MD, Departments of Ophthalmology and Neurology, Saint Louis University, 1755 S. Grand Boulevard, St. Louis, MO 63104; E-mail: sangeeta.khanna@ health.slu.edu Garcia and Khanna: J Neuro-Ophthalmol 2021; 41: e703-e707 FIG. 1. Fundus examination 4 weeks after carbon monoxide poisoning, demonstrating bilateral disc edema and peripapillary hemorrhages. Patient endorsed worsening vision and pain behind both eyes. e703 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence FIG. 2. Imaging findings of raised intracranial pressure seen in our patient. A. MRI orbit: T2 axial cuts show flattening of the globes right. left as indicated by the arrow. B. MR venogram before placement of ventriculoperitoneal shunt showed narrowing of dural venous sinuses, most pronounced in transverse sinuses and parts of superior sagittal sinus (arrow). C. Repeat MRV after placement of ventriculoperitoneal shunt shows increased patency of the dural venous sinuses after normalization of the intracranial pressure. MRV, MR Venogram. e704 affinity for hemoglobin which is 240 times greater than oxygen. This results in a reduced oxygen carrying capacity of hemoglobin, tissue hypoxia, and neuronal necrosis. CO poisoning causes central nervous system damage, and the effects are not limited to initial presentation and may present days to weeks after the cessation of initial symptoms in up to 40% of individuals (1). Neurologic and neuropsychiatric manifestations of CO poisoning are encountered more frequently and include headache, nonfocal alteration in mental state, confusion, dizziness, in milder cases and seizures, loss of consciousness, ataxia, brain infarction, and death in severe cases. Delayed neurological sequelae (DNS) can develop 2–40 days after exposure and include amnesia, apraxia, agnosia, parkinsonism, incontinence, and peripheral neuropathy (1,2). Neuro-ophthalmic complications of carbon monoxide poisoning are not encountered frequently but can include devastating visual loss. There have been case reports of cortical blindness, toxic optic neuropathy, asymptomatic retinal venous congestion, and retinal hemorrhages. These are summarized in Table 1. Latency of visual symptom onset after poisoning can vary from 3 to 30 days as in our patient who reported onset about 4 days after exposure and progressively got worse. Development of intracranial hypertension is not well documented in the literature. A few case reports did mention mild papilledema with retinal venous congestion without spinal tap confirmation on mechanism (Table 1). One report indicated development of cerebral venous sinus thrombosis after CO poisoning (3). Our patient did not have venous sinus thrombosis. We believe our patient is the first welldocumented case report of severe intracranial hypertension developing as DNS of CO poisoning unrelated to venous sinus thrombosis. We speculate that the raised ICP may be related to the increase in cerebral blood flow as a mechanism to combat hypoxia (4). In addition, this case highlights what has been long recognized: that initial COHb level cannot be solely relied on to diagnose the severity of CO poisoning, particularly of the nervous system (2). Our patient was classified as mild at the initial hospital admission based on the COHb levels, but he clearly showed severe disease with acute loss of consciousness and then delayed drastic vision loss and severe intracranial hypertension. The literature supports the use of hyperbaric oxygen (HBO) within 24 hours of CO poisoning especially in moderate to severe poisoning as determined by clinical presentation (rather than COHb levels). This significantly reduces the risk of DNS which can be devastating as seen in this case. The role of HBO as treatment after manifestation of DNS is not well understood and is an area of future research (5). Garcia and Khanna: J Neuro-Ophthalmol 2021; 41: e703-e707 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Garcia and Khanna: J Neuro-Ophthalmol 2021; 41: e703-e707 Visual Sx Latency Ophthalmologic from Carbon Sex Presentation Other Symptoms Monoxide Exposure Ophthalmologic Examination Age Bilchik (6) 49 F Asymptomatic Weakness, headache NA 54 M Asymptomatic Weakness, headache NA 11 M Asymptomatic Weakness, headache NA 28 M Vision loss, cortical blindness M Vision loss, cortical blindness F Vision loss, optic neuropathy Headache, photophobia 5 days Comatose, spastic quadriparesis Comatose ,5 days Fundus and light reflex normal ,7 days M Vision loss, cortical blindness F Vision loss, optic neuropathy M Vision loss, optic neuropathy LOC followed by 7 days headache Fix and Disc edema OU, follow OD, peripapillary hemorrhage OU, no No fixation lumbar puncture OS LP OU Intact light reflex, fundus normal, total blindness 20/200 OD, Bitemporal disc 20/120 pallor, paracentral OS scotoma OU NA Bitemporal pallor, central scotoma, and peripheral constriction OU Duncan (7) Katafuchi (8) 3 Ferguson (9) 5 Quattrocolo (10) 22 Simmons (11) 43 None 3–4 days Cognitive deficits NA Swollen disc and retinal heme, cotton wool spots OU; lumbar puncture normal Retinal heme and exudate OU; lumbar puncture normal Swollen disc and retinal heme, cotton wool spots OU Normal Initial VA Final VA Follow-Up Intervention 20/20 OU 20/20 OU 21 days NA 20/20 OU 20/20 OU 21 days NA 20/20 OU 20/20 OU 9 months NA LP OU 20/20 OU 1 month Absent LP Absent LP 3 months Mask O2 dopamine infusion Nasopharyngeal O2 20/30 OD, 28 days 20/200 OS NA “Normalized” 90 days NA 20/120 OD, 20/60 OS 42 days Hydroxocobalamin CF OU 10 years NA Clinical Correspondence Author 49 e705 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. TABLE 1. Summary of the literature Author Age 30 Ersanli (12) 34 32 Karakurum (13) 18 Levin (14) 5 Uzuner (3) 44 Visual Sx Latency Ophthalmologic from Carbon Sex Presentation Other Symptoms Monoxide Exposure M Vision loss, optic neuropathy F Vision loss, cortical blindness F Vision loss, cortical blindness F Vision loss, cortical blindness M Vision loss, cortical blindness F Photophobia LOC NA LOC followed by 3 days nausea, vomiting, headache, memory loss LOC followed by 6 days memory loss LOC 10 days Garcia and Khanna: J Neuro-Ophthalmol 2021; 41: e703-e707 LOC followed by NA stupor and rigidity Headache, NA nausea, vomiting Ophthalmologic Examination Initial VA Final VA Follow-Up 20/30 OU 20/30 OU 3 years Bitemporal pallor, central scotoma, cupping OU Papilledema OU - mild HM 10 cm 20/100 OD; 61 days 20/130 OS OD, CF grade 1, no lumbar 10 cm OS puncture, normal light reflex Normal fundus, normal light reflex Normal 20/100 OD, 20/28 OU 20/200 OS LP OU 20/25 OU Vitreous hemorrhage NA Papilledema OU, No lumbar puncture, venous sinus thrombosis NA Intervention NA HBO started 8th day 42 days HBO started 6th day 12 months Nasal O2, dexamethasone 20/30 OD, 20/40 OS 3 months NA 2 months HBO,* vitreous tap, intravitreal Abx HBO* *Time since HBO initiation not available. Abx, antibiotics; CF, count finger; HBO, hyperbaric oxygen; HM, hand movement; LOC, loss of consciousness; LP, light perception; NA, not available; OU, both eyes; Sx, symptoms; VA, visual acuity. Clinical Correspondence e706 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. (Continued ) Clinical Correspondence STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: J. Garcia and S. Khanna; b. Acquisition of data: J. Garcia and S. Khanna; c. Analysis and interpretation of data: J. Garcia and S. Khanna. Category 2: a. Drafting the manuscript: J. Garcia and S. Khanna; b. Revising it for intellectual content: J. Garcia and S. Khanna. Category 3: a. Final approval of the completed manuscript: J. Garcia and S. Khanna. REFERENCES 1. Choi S. Delayed neurologic sequelae in carbon monoxide intoxication. Arch Neurol. 1983;40:433–435. 2. Piantadosi CA. Carbon monoxide poisoning. New Engl J Med. 2002;347:1054–1055. 3. 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