SUDDEN VISUAL DISTURBANCE IN AN AIRCREWMAN – INVESTIGATION AND DIFFERENTIAL DIAGNOSIS

A 48-year-old Blackhawk loadmaster aircrewman experiences sudden visual disturbance while driving his car to work; more specifically pixilation and serpentine patterning in the right visual field of the right eye. The aircrewman stops driving, hands over to his passenger and presents to Oakey Aviation Medical Centre. His is distressed and fears he has suffered a stroke. A 72-hour history is taken with nothing unusual noted, apart from spray painting his R/C aircraft with Tamiya paint in a closed room without ventilation the previous day.

The aircrewman presents with a distressed appearance, mild pallor and diaphoresis. Pulse is 84 regular, BP 122/74, RR 20, SaO2 99% and T 36.2. Heart and lung auscultation is normal and no carotid bruits noted. VA is 6/6 bilateral uncorrected, PEARLA, fundoscopy normal confrontation test is normal, visual fields are normal and no ptosis noted. All cranial nerves are normal; there is no motor or sensory deficit and speech and ECG (SR 80) are normal.

Previous medical history reveals no operations or chronic diseases and no allergies. BMI is 28.7, blood pressure is normal and total cholesterol is 4.9. There is no history of previous migraine or recurrent headaches and no family history of migraines. The aircrewman reports he was a long-timer smoker, but had given up a few weeks ago and was using e-cigarettes.

The aircrewman is referred to Toowoomba Emergency Centre for further investigations. Visual sensation moves laterally and fades within 60 minutes; and he is left with mild frontal headaches in both hemispheres. These are non-pulsating – dull in nature, with no nausea or photophobia/phonophobia. Neurological examination finds no unusual features. Bloods FBC, ESR, BSL, E/LFT are all normal, along with a CT scan of the brain to look for ischemia. The case is discussed with the on-call ophthalmologist over the phone and the aircrewman is reassured that he most likely suffered a migraine.

The aircrewman is discharged home the same day. He is reviewed by the aviation Medical Officer the next day and is found to have made a full recovery.

Is the diagnosis migraine or stroke?

The most likely diagnosis is migraine with aura; retinal migraine; typical aura without headache (Acephalic migraine); or simple visual hallucination.

Secondary causes could be CTA/TIA; vascular (eg. Aneurysm, carotid artery dissection); brain tumour (primary or secondary); Multiple sclerosis; or ophthalmological (eg. Detached retina).

Visual effects in migraine are caused by cortical spreading depression (CSD) rather than vasoconstriction.

The most common positive effects include Scintillation scotoma and fortifications. Less common are kaleidoscope, crackled glass, photopsia (flashes) and pixilation. Negative effects include blurring, greyout, blackout, tunnel vision, homonymous hemianopia, desaturation and cortical blindness.

The question is: should we investigate this or not? Perhaps a neurologist would say it’s most likely a migraine; however the literature shows there’s quite a raft of differential diagnosis. In this case there are 300 to consider.¹

In most cases, they are clear-cut and there is no need to investigate. However, there are certain criteria where in the literature at least the neurologist decides investigation is warranted. These include onset in those aged greater than 50 years; some neurological lasting deficits; no typical headache (possible acephalic migraine) or unusual features like first or worst headache.

Other criteria where migraine investigation is warranted in the literature includes all anterior visual pathway migraine (retinal migraine) and acephalic migraine²; atypical aura (not visual), affective movement, sensation or cognition³; occasionally typical aura caused by focal cerebral lesion⁴; in cases of diagnostic uncertainty, or to demonstrate diagnostic competency; upon patient request or expectation; or ‘just to be safe’ or for medico-legal reasons.

Retinal migraine is a very rare condition (1 in 200 migraineurs), but up to half of cases with recurrent attacks show permanent monocular visual loss.^5,6

CT is first-line investigation for intracranial haemorrhage e.g. acute SAH suspected, bony pathology, thunderclap headaches. An MRI will pick up multiple other pathology such as: Vascular process, arteriovenous malformation, aneurysm, thrombosis; diffusion weighted image changes; white matter abnormalities, MS, or optic neuritis; inflammation such as vasculitis, abscess or neoplasia; posterior fossa and pituitary pathology; and subtle subdural/epidural haematoma. For investigations of headaches, MRI is the preferred modality.¹

The neurological examination was normal. A review of the MRI and CT scan found slight hypoplastic corpus callosum on the MRI, which the neurologist said could be incidental. However, a referral to an ophthalmologist was considered important to rule out ocular pathology.

The neurologist’s opinion was most likely migraine, with a differential diagnosis of retinal migraine. However, due to the patient being an aviator, an echocardiogram and carotid Doppler was ordered as part of the stroke workup.

A follow up with the ophthalmologist found a normal eye examination. The neurologist finds normal echo and carotid Doppler; TIA was thought unlikely.

The aircrewman experienced no further events. It was considered most likely that the aircrewman experienced a migraine, triggered by spray paint solvents in a closed room. He was advised to avoid re-exposure to the trigger circumstances, and to return for review if any further events occur. He is grounded pending follow up the aviation medical officer after investigations.

When considering aeromedical disposition of a migraine, the risk is potential incapacitation due to aura or subsequent headache. Of primary concern is potential neurological deficit: visual impairment, paresis, paraesthesia; distraction from task, photo/phonophobia; pain, nausea, vomiting, vertigo (common); or impaired judgement and mood changes.

We looked into a number of triggers. Was it the spray paint fumes, or was it a food trigger? Was it the use of e-cigarettes?

There are a number of possible triggers to consider: food and wine, cheese⁷, chocolate, preservatives (nitrates), enhancers (MSG, sweeteners) or lack of food or dehydration; medications, eg OCP, Sildenafil, nitrates; lifestyle (fasting, smoking, caffeine, fatigue, sleep disturbance, stress); activity (physical training, sexual intercourse); external factors including the weather, altitude, strobe lights or computer screens; or exposure to noxious substances, in this case vaping e-cigarettes or spray painting. In the aviation environment, anti-G strain and the use of NVGs have been cited as migraine triggers^8,9.

There have been some anecdotal reports about the use of e-cigarettes (or ‘vaping’) causing migraine-like headache and seizure. New generation devices can deliver a vapor containing 1mg of nicotine with substantial ‘hit’, although the surge is only one third of a normal cigarette.¹⁰

The use of e-cigarettes is becoming increasingly common in the community, possibly driven by the perception of them being a less-harmful alternative to smoking tobacco. Exposure to toxic substances through the use of e-cigarettes is far lower compared to tobacco cigarettes (with 4000+ noxious substances being present in tobacco smoke). Compared to smoking, e-cigarettes exert minimal or no effect on lung and cardiovascular function, and do not impact levels of blood CO.¹⁰

Several controlled trials in small study populations reported no relevant adverse effects¹⁰, but long-term safety data is not available. The US Food and Drug Administration (FDA) has received anecdotal reports about unwanted effects attributed to the use of e-cigarettes, including migraine-like headaches and seizure.

E-cigarettes – including the devices and the nicotine ampoules – are not TGA approved in Australia, and they are unlikely to be so long as nicotine is considered a “Schedule 7 dangerous poison”. However, the use of e-cigarettes can be prescribed by a medical practitioner for personal use in certain cases¹¹.

The delivery of nicotine through e-cigarettes is powered by high capacity/high energy lithium battery, and these batteries are considered an aviation safety hazard due to their link with causing on-board fires.

The use of e-cigarettes is fairly recent, but three aeromedical considerations have emerged that are worthy of further study. It is not yet clear whether ‘vapers’ are considered ‘smokers’ when assessing cardiovascular risk. Is the delivery of nicotine via an e-cigarette considered nicotine supplement, or prevention of withdrawal from a smoker who is prevented from using tobacco prior to flight? To what extent does vaping enhance, or degrade, performance? The use of e-cigarettes is becoming increasingly common, and it is important for the aeromedical community to consider these issues.

Pilot incapacitation from migraine has been linked to several aviation and transport accidents and incidents, both in Australia^12,13, and international^14-16. It is clear that an accurate diagnosis and characterisation of migraine is important for flight safety.

Diagnosis was solely based on history and symptoms, and by exclusion of other pathology. Migraine with aura was the most likely diagnosis, although no second attack was observed as per the IHD2 criteria. Was it a retinal migraine? Initial symptoms only affected the right eye, but the neurologist reported that the right visual field was affected. It was unclear what role potential triggers played. Aeromedical disposition relies effectively on patient reported symptoms, as there is no way of monitoring them.

The aircrewman underwent frequent review for a four-month period following the incident. During that time he abstained from potential triggers, particularly spray paint.

Advice about e-cigarette use in the Australian Defence Forces was sought from SO1 Aviation Medicine, 16^th Aviation Brigade - the use of e-cigarettes is not permitted for aviators.

The aircrewman kept a headache diary, and reported no further visual disturbance or headaches. He was able to return to flying ‘as or with second loadmaster’ eight weeks after the event.

Disclaimer: The views expressed in this article are those of the author, and do not reflect a position of the Editor or Committee of the Australasian Society of Aerospace Medicine.