Severe obstructive sleep apnea diagnosed after non-arteritic anterior ischaemic optic neuropathy in a young man

Abstract

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in older individuals but may also occur in younger patients. A 30-year-old man presented with a 2-day history of right eye painless vision loss and was found to have right optic disc oedema and a left ‘disc-at-risk’. He was diagnosed with right NAION and review of symptoms revealed witnessed apnea at night and episodes where he woke up gasping for air, concerning for obstructive sleep apnea (OSA). A formal sleep study revealed severe OSA and he was treated with continuous positive airway pressure to reduce his risk of fellow eye involvement and reduce his overall cardiovascular risk. OSA should be considered in every patient with NAION, especially in younger patients without any additional risk factors.

Background

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in older individuals.¹ Clinical features of NAION include acute vision loss, typically an altitudinal visual field defect and optic disc oedema that resolves usually within 6–11 weeks.¹ NAION is a disease typically seen in patients over 50 years of age, who have an anatomic predisposing factor, the so-called ‘disc-at-risk’ and systemic vascular risks such as hypertension and diabetes mellitus.¹ In recent years, the association between obstructive sleep apnea (OSA) and NAION has been increasingly recognised.^{2 3} NAION in patients under 40 years of age is uncommon⁴ and it has been suggested that OSA is a strong risk factor particularly in this age group.⁵ We describe a case of NAION in a 30-year-old man which led to the diagnosis of severe OSA, emphasising the association between OSA and NAION and the need to screen for this condition especially in younger individuals without any additional risk factors.

Case presentation

A 30-year-old man presented with a 2-day history of right eye painless vision loss. He noticed the symptom on awakening in the morning, and described it as ‘a large black shadow just below the centre of vision’. He denied pain or pain with eye movements.

His medical history was remarkable for asthma, anxiety and depression. His medications included sertraline, trazodone, salbutamol puffers and lorazepam on an as needed basis. He denied use of phosphodiesterase-5 inhibitors or amiodarone. On further questioning, he mentioned that his partner frequently observed apneic episodes during sleep and frequent snoring. He recalled episodes where he woke up from sleep choking and gasping for air. He also endorsed daytime fatigue.

On examination, he was found to have blood pressure of 162/112 mm Hg and heart rate of 73 bpm. He had a muscular build, was 191 cm tall and weighed 114 kg (body mass index 31.2 kg/m²), and neck circumference of 42 cm. He had normal visual acuity of 20/20 in both eyes, and a right relative afferent pupillary defect was noted. Dilated fundus examination showed optic disc oedema in the right eye and a normal appearing disc in the left eye (figure 1). There was a small cup-to-disc ratio in the left optic disc, which is consistent with the so-called ‘disk-at-risk’ (figure 1). Humphrey 24-2 SITA-Fast visual field testing showed a right inferior altitudinal defect and was normal in the left eye (figure 2). He had a normal peripheral retinal examination. Ocular motility and alignment and cranial nerve function were normal.

Figure 1.

Fundus photos at presentation demonstrating right optic disc oedema (primarily in the superior portion of the optic disc) and a left eye ‘disc-at-risk’.

Figure 2.

Humphrey visual field testing (24-2 SITA-Fast) at presentation demonstrating a right eye altitudinal inferior defect.

The clinical diagnosis if right NAION was made based on the acute symptoms, characteristic visual field loss and segmental optic disc oedema. He had significant symptoms of OSA and we therefore referred him for a formal sleep study. His blood pressure was also significantly elevated and he was urgently referred to his primary care physician for management of this. He was also advised and counselled on the importance of weight loss and received formal consultation on this with his primary care physician and a dietician. An MRI of the brain and orbits with contrast and a workup for hypercoagulable state were arranged.

Investigations

The results of the sleep study showed that he suffered from severe OSA with a total apnea–hypopnea index severely increased at 68.4 per hour, further increased to 96.9 per hour in rapid eye movement (REM) sleep. Oxygen saturation was below 90% for 3% of the time. Out of 49.8 per hour arousals 40 per hour were respiratory-related arousals.

The remainder of the investigations was normal including MRI of the brain and orbits with gadolinium, HbA1c and lipid profile. A workup for a hypercoagulable state including erythrocyte sedimentation rate (ESR), C reactive protein (CRP), antiphospholipid antibodies, lupus anticoagulant assay, protein C and S assay, International Normalized Ratio and homocysteine were all within normal limits. A nontreponemal syphilis screen was also negative.

Differential diagnosis

The diagnosis of NAION was substantiated by the presence of acute onset of unilateral visual loss from an optic neuropathy, altitudinal visual fild defect, optic disc oedema and ‘disc-at-risk’ in the fellow eye. The fellow eye served as a marker of what the involved eye looked like before the onset of optic disc oedema. He had a significant risk factor for NAION given his symptoms of severe OSA. The differential diagnosis for a unilateral optic neuropathy includes inflammatory, compressive or infectious etiologies. He had no pain or pain with eye movements to suggest optic neuritis and his symptoms were of sudden onset, arguing against compression of the optic nerve, which is usually of gradual onset. He was not immunosuppressed and had no other risk factors for infection.

Treatment

There is no established treatment for NAION and the primary focus was on optimising his underlying vascular risk factors. He was started on candesartan for his blood pressure and continuous positive airway pressure (CPAP) for severe OSA. He was also counselled on the importance of weight loss and working with his primary care physician and dietician on this.

Outcome and follow-up

At 3-month follow-up, the visual acuity of the affected eye is 20/25. The optic disc oedema resolved, and there was superior-temporal segmental optic pallor (figure 3). Humphrey visual field showed a persistent inferior altitudinal defect presentation (figure 4). His blood pressure was improved at 126/83 mm Hg and he had lost 2 kg.

Figure 3.

Fundus photos at a 3-month follow-up demonstrating right optic disc superior pallor and an unchanged left eye ‘disc-at-risk’.

Figure 4.

Humphrey visual field testing (24-2 SITA-Fast) at a 3-month follow-up demonstrating a right eye altitudinal inferior defect.

Discussion

Although the exact mechanism of NAION pathogenesis has not been fully elucidated, it is generally believed that NAION is related to a failure of the microvascular autoregulation within the prelaminar portion of the optic nerve head.^{1 6} The most widely accepted hypothesis of NAION pathogenesis is that a transient event of hypoperfusion in a crowded optic disc causes infarction and swelling of ganglion cell axons, leading to compression of microvasculature in the optic nerve head. A vicious cycle of ‘infarction–edema–compression–more infarction’ within the anatomically predisposed constricted optic disc space leads to acute onset of edematous optic neuropathy.^{1 6}

NAION is typically a disease of older individuals and uncommon in young patients.¹ In a series of 747 consecutive patients of NAION, 77% were 50 years old and above, only 1.9% were under 30 years of age.⁴ Scattered case reports of young patients with NAION often have disc-at-risk’ in combination with a major precipitating event such as blood loss,^{7 8} hypovolemia/hypotension during dialysis^{9 10} or a hypercoagulable factor such as phospholipid antibodies.¹¹ The current NAION patient, however, was a 30-year-old young man with ‘disc-at-risk’, but the precipitating factor was not immediately clear at the presentation until a review of symptoms related to OSA was obtained. A sleep study later on revealed an undiagnosed severe OSA. This case is an example to support the idea of recent literature that OSA is a strong risk factor for NAION.2 3 5 12–14

Numerous studies have suggested the association between NAION and OSA by evaluating the prevalence of OSA in NAION patients and vice versa.2 3 5 12–14 The prevalence of OSA in NAION patients was reported to be 71% (12 of 17 cases) by Mojon et al ² and 89% (24 of 27 cases) by Palombi et al.³ On the other hand, the prevalence of NAION among patients diagnosed with OSA was studied by Stein et al,¹³ who reviewed approximately 2 million billing records to determine the incidence of NAION stratified to OSA status. The results suggested that OSA not treated with CPAP posed a 16% increase in the risk of developing NAION. Most recently, a large longitudinal health insurance database study among Asian population showed that OSA patients had a 1.95-fold higher risk of NAION compared with controls in all age groups and that the risk was significantly higher (adjusted HR: 4.21) in patient less than 45 years old and male individuals (adjusted HR: 1.93).¹² Many of these studies were included in a systematic review and meta-analysis, which concluded that there was robust evidence that OSA was a strong independent risk factor for NAION with more than a sixfold increase in risk.¹⁴

The mechanism by which OSA is linked to NAION has not been clearly understood, speculated mechanism includes OSA-induced direct hypoxic injury to retinal ganglion cell axons,⁵ increased intracranial pressure during apneic episodes causing compression at the disc² and hypoxia-reoxygenation causing oxidative stress, leading to capillary endothelial damage and autoregulatory dysfunction.³ The benefit of CPAP ventilation in NAION has not been established in prospective trials. Behbehani et al ¹⁵ described three OSA patients who developed NAION while receiving CPAP, the authors questioned the role of CPAP in preventing NAION. More recently, Aptel et al ¹⁶ reported a cohort of 89 NAION patients with up to 3 years follow-up data. They found that NAION patients with OSA have significantly higher chance of having a second attack in the fellow eye compared with non-OSA NAION patients. Moreover, multivariate analysis in the study showed that non-adherence to CPAP treatment in NAION patients with severe OSA increased the risk of second eye involvement (HR, 5.54). The current consensus is that, as a modifiable condition, OSA should be treated in NAION patients in an attempt to minimise the risk of NAION recurrence.¹⁷

In summary, we described a young male patient who developed NAION at 30 years of age likely as a result of undiagnosed severe OSA. This case highlights the association between OSA and NAION. All NAION patients, especially the younger ones, should be screened for OSA-related symptoms and signs. OSA and other modifiable risk factors should be properly addressed to minimise the risk of NAION in the fellow eye or the rare recurrence in the same eye.

Learning points.

• Non-arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in older individuals, but may also occur in younger ones.

• Risk factors for NAION include obstructive sleep apnea (OSA), medication use (eg, phosphodiesterase-5 inhibitors), hypertension and diabetes mellitus.

• Younger patients with NAION should be screened for OSA, especially if there are no additional risk factors and the patient has symptoms such as frequent snoring, apneic episodes or daytime fatigue.

• Treatment of OSA with continuous positive airway pressure may reduce the risk of NAION in the fellow eye and also has cardiovascular benefits.