'Lost My Way' - Transient Topographic Amnesia: A Bizarre Manifestation of Migraine.

Sir,

Migraine is a common disease that can present with bizarre manifestations. Many perceptual experiences and focal deficits have been reported in migraine and these have been attributed to the spreading cortical depression affecting corresponding areas of the cerebral cortex.[1] Here, we report a peculiar experience of one of the authors during a migraine aura and discuss its probable mechanism and its implications on evaluation of cases with transient topographical amnesia (TTA).

(All the places in this report are typed in italics. These places are in South Kerala, India, and may be unfamiliar to readers).

A 31 year old, right handed male, DGY, the first author of this article, a known migraineur, experienced a migrating scotoma (in his right visual field) while he was at work at Venjaramoodu. He had a family history of migraine, and his father and father's two siblings were migraineurs. His past history was apparently normal except that he had allergic rhinitis and migraine with visual aura (~1–3 episodes per year) since his school days. He was not on prophylaxis. He had some extended academic work the previous day and had lost sleep, the previous night. With the onset of scotoma, he decided to take rest on his desk. The scotoma enlarged: its position and shape altered over next 15 min and later the scotoma disappeared. There was a flickering edge to the scotoma. After 20 min of the onset of scotoma, the headache started. The headache was hemicranial to start with, but later became diffuse. It was pulsatile, was associated with photophobia and phonophobia, was aggravated with shaking of head and prevented him from performing activities. After around 30 min, he noticed another scotoma (left visual field). It also changed its position and shape over next 10 min and later disappeared. Soon the headache worsened. Unable to find a suitable area to rest at his workplace, he decided to drive back home to take rest in a calm environment. The journey that he had to undertake was a 33-km drive from his workplace – Venjarammoodu – to his home – Trivandrum. The route was very familiar to him as he had been driving to his workplace, most of the days for the past one year. The time was around 12 noon. As he began his drive, he was disabled by intense headache, sunlight, and glares of light reflecting from the vehicles on his way. After around five km, he developed another scotoma (again, in his left visual field). He judged that his scotoma was in the peripheral field of vision and he felt that he could drive and reach home soon, to take rest. After 7 km from Venjarammoodu, he reached the junction at Vembayam from where he had to take a right turn to go to Trivandrum [Figure 1]. He had been driving along this route for around one year and had been thorough on the roads and navigation. However, he was ‘unable’ to take the right turn, but continued to drive along a wrong route [Figure 1]. He saw the signboards, which he could read, but felt strange about the name of the places. As the central vision was clear, DGY believed that he would be able to continue with his driving. He drove slowly, but as he drove further, he became more and more confused. He saw the place boards, could read the letters but could not ‘link the word to the place.’ He parked the car by road-side and got out. Then he realized that he needs to seek help. He waved his hands for help and a motor cyclist, X (name concealed), stopped by. DGY explained to X that he was a doctor and that he was having an attack of migraine, but strangely he could not say from which place he came from or to which place he was going to. DGY asked X about the place where they were, and X said that it was Nedumangad (a town almost 8 km off the route to his residence). DGY heard the word Nedumangad but he could not identify it as a place. His speech was clear as reported by X later. He did not feel weakness of any part of the body, double vision, or abnormal sensations. DGY thought about differential diagnoses of his own condition and made a mental shortlist of acute cerebrovascular event an impending seizure and acute encephalopathy. DGY phoned RSW, his medicine professor (the 2nd author of this article). DGY narrated briefly about his scotomas and headache and told him that he was driving home, but then he was ‘lost’ and confused. RSW provisionally diagnosed the condition to be a migraine aura, asked DGY to lie down in the car and take rest and asked him to hand over the phone to X. DGY also phoned his family members who drove to the spot. Meanwhile, DGY slowly recovered from the amnesia in 10–15 min, after parking the car. The scotoma had disappeared 15 min earlier, while he was driving the car. He felt very tired and uneasy due to headache. DGY then ‘realized’ that he had taken a wrong route from Vembayam and that he has then reached Nedumangad instead of turning to Trivandrum [Figure 1], all places which were very familiar to him. DGY's relatives took him to hospital for medical attention, with the help of X.

Figure 1

(a) The view of Vembayamjunction on the road from Venjaramoodu. The road to the right is to Trivandrum, which was the road to DGY's residence, but he took the wrong route (straight) to reach Nedumangad. Source – Image in public domain. (b) The aerial view of the places in three-dimensional rendition in Google Maps. The line shows the intended road. Source – Google Maps (image in public domain)

RSW clinically examined DGY. His vital signs were stable. He was conscious and oriented. He continued to experience headache when he was examined. Higher mental functions were normal. A neurological examination was unremarkable. The Mini–Mental State Examination was also normal. RSW diagnosed it as a case of migraine with aura. RSW ordered for immediate intravenous administration of 8 mg dexamethasone to DGY. He was also given an oral analgesic (paracetamol 500 mg) and then he was sent home. The headache lasted for around 8 h. He started DGY on the prophylactic drug propranolol at a dose of 40 mg, bedtime for 6 months. He later ordered magnetic resonance imaging (MRI) of the brain to rule out any other structural cause for migraine. Plain and contrast MRI were done by NJJ (the 3rd author of this article) and were found to be normal. While on prophylactic medication, he had very infrequent attacks of milder headache. However, there was no visual aura or topographic amnesia associated with them. RSW tapered the dose of propranolol after 6 months and stopped it completely at 9 months. DGY now uses sunglasses while driving to avoid triggers like glare, sleeps adequately, and avoids stress and identified triggers. After the prophylaxis was stopped, he experienced one episode of migrainous headache associated with visual aura, which was treated with analgesics. He never had an episode of topographic amnesia before or after this incident.

Human navigation is a result of complex networks in the cerebral cortex. While the dominant hemisphere of the cerebrum is said to be involved in the language functions,[2] the non-dominant hemisphere is said to have a specialized role in spatial orientation.[3] The regions of brain said to be directly involved in human navigation are the dorsal parietal cortex and the hippocampus along with parahippocampal networks, of the non-dominant hemisphere of the cerebrum. The role of the hippocampus in navigation as an internal “GPS” has been proven in animal experiments.[4] The place cells in hippocampus and grid cells in the nearby entorhinal cortex create a spatial memory map, and these coordinates are used by the dorsal parietal cortex to navigate through environment.[5]

The present case seems to be a TTA, a term used to describe a temporary inability in the wayfinding process due to improper functioning of the brain circuits necessary for human navigation. The clinical features of the aura and headache in the present case fulfilled the International Classification of Headache Disorders 3rd edition beta as a migraine with aura.[6] The understanding of the pathophysiology of migraine has drifted from the old “vascular theory” of transient vasoconstriction and rebound vasodilatation to cortical spreading depression (CSD).[7] The pathophysiology of the clinical presentation in our report may involve the CSD reaching the right temporal lobe and affecting the hippocampus and the parahippocampal pathways and parietal cortex of the right (nondominant) side, causing disturbance in the normal networks involved in spatial navigation. It correlates with the fact that the last two scotomas DGY experienced prior to losing directional sense were in the left halves of the visual fields. The ability to ‘read’ the name of a place, but not being able to ‘link the word to the place’ also seems to be a feature of topographical amnesia. It is to be noted that DGY did not have deficits in speech or defects in higher mental functions as he was able to explain to X about his profession and medical problem and as he was able to derive ‘diagnostic differentials’ in a logical sequence in congruence with his education and training. His global memory seemed to be intact as he was able to call his medicine professor and his relatives from his mobile phone contact list and narrate his medical problems. In this case, a differential diagnoses of transient ischemic attacks, complex partial seizures, and transient visual obscurations associated with brain tumors were considered. Plain and contrast MRI were done and were found to be normal. Complex partial seizures were less likely as the aura was prolonged, nonstereotypic, and was soon followed by migrainous headache. The patient did not have any known or newly diagnosed common risk factors of stroke. Hence, transient ischemic attack was also considered to be less probable.

Stracciari et al. described a series of ten cases of TTA and suggested it to be a benign cognitive disorder.[8] Cammalleri et al. reported an interesting case of recurrent short (5–10 min) episodes of TTA where a patient could not orient himself in the familiar streets of his native village.[9] On MRI, the patient had a lesion (probably angioma) near the middle-third of the right cingulate cortex. Area 23 of the right cingulate cortex is located at a strategic point in the networks linking the right parietal cortex and the right parahippocampal networks. They suggested that transient epileptic discharges from damaged cingulate cortex to parahippocampal and parietal cortex may account for the TTA. This patient was given a daily oral dosage of 900 mg carbamazepine and no similar episodes occurred later. Although there have been similar documented descriptions of TTA in patients with focal deficits in the right cerebral hemisphere,[10] right retrosplenial lesions,[11] right posterior cingulate cortex,[12] and in generalized neurodegenerative diseases such as dementia,[13] particularly Alzheimer's disease, the occurrence of TTA in a context of migraine has not been reported.

The clinical implication of the present report can be the possible inclusion of migraine in the differential diagnoses of TTA when the clinical scenario – past history of migraine, aura and headache – is appropriate. We stress that even a single episode of TTA warrants a detailed neurological examination, a neuropsychological assessment, and imaging of the brain to rule out other structural causes. Driving a motor vehicle may not be advisable for a migraineur while having a migraine aura, however tempting it is to ‘reach home fast’.

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Conflicts of interest

There are no conflicts of interest.