Natural recovery from long-lasting generalised dissociative amnesia and of cerebral blood flow

Abstract

A 40-year-old man presented with generalised dissociative amnesia. At 2 weeks after onset, N-isopropyl-[¹²³I] p-iodoamphetamine-single-photon emission CT imaging of the brain revealed hypoperfusion in the right medial temporal area. Organic brain damage was ruled out. His inability to recall information was attributed to psychological stress related to his employment. Consistent with this diagnosis, his generalised dissociative amnesia lasted 6 years and 10 months; however, he recovered from amnesia naturally on starting a new job. Perfusion of his right medial temporal area also returned to normal levels. Longitudinal reports for generalised dissociative amnesia with natural recovery are exceedingly rare. It is important to confirm whether dissociative amnesia and cerebral blood flow recover in parallel, even in cases where dissociative amnesia is long-lasting.

Background

Generalised dissociative amnesia is characterised by the sudden loss of a person’s whole autobiographical episodic memory in the absence of accompanying organic brain damage. Typically triggered by psychological stress or trauma, this severe condition was previously called psychogenic amnesia. Previous studies using standard MRI did not identify substantial structural changes in the brain of patients with generalised dissociative amnesia; however, functional neuroimaging studies using positron emission tomography, single-photon emission CT (SPECT) and functional MRI reported changes in metabolic activity or blood flow in the prefrontal, frontal or temporal areas.¹ A case study report of 14 patients with dissociative amnesia identified hypometabolism of the right inferolateral prefrontal cortex.²

In Japan, the first case of generalised dissociative amnesia was reported in 1950. Following a case study report in 1992,³ several additional case studies described the use of functional neuroimaging to study generalised dissociative amnesia.⁴ Hypoperfusion in areas of the brain where memory retrieval was diminished during amnesia was reported for a few of these cases. However, long-term follow-up studies using neuroimaging before and after recovery of generalised dissociative amnesia are exceedingly rare.

The present case is a patient who had lost his whole life’s memory in response to psychological stress. After greater than 6 years following the onset of amnesia, his memory recovered, naturally. Concurrently, perfusion in the temporal lobe, which was reportedly decreased soon after the onset of amnesia, returned to normal levels. Written informed consent was obtained from the patient for publication of this case report and accompanying images.

Case presentation

A 40-year-old man, who had total amnesia, visited the psychiatry department of Hokkaido University Hospital with his family. He had lost his autobiographical and episodic memory 2 weeks prior and was very confused. On the day of amnesia onset, he suddenly could not even remember his own name. Fortunately, his friend found him roaming the street, and took him to his family. Although he could recognise his own name after being taught it by his friend, he could not recall it by himself.

The man was born in Sapporo, Hokkaido Japan, and had an older brother and sister. He was raised in an old-fashioned household with a strict upbringing and grew up to become an introversive and gentle person. A few years before, he visited the hospital, he was running a bookstore. However, the bookstore went bankrupt and he lost his job. Although the man attended a vocational training school to gain skills for a new job, he was unable to find new employment because there were no positions available until after his graduation. He lost his whole autographical and episodic memory on the last day of vocational training school. A clear connection was observed between the loss of his job and sudden onset of dissociative amnesia.

The man was admitted to our hospital 2 weeks after the onset of total amnesia and received N-isopropyl-[¹²³I] p-iodoamphetamine-SPECT (IMP-SPECT), MRI, electroencephalogram (EEG) and neurocognitive tests. IMP-SPECT using a three-dimensional stereotactic surface projections revealed hypoperfusion of the right ventral area of the medial temporal lobe (figure 1). By contrast, neither MRI nor EEG revealed any significant brain damage. Neuropsychological tests revealed a slight decline in cognitive function, which recovered within 3 months. The neuropsychological tests employed were as follows: Wechsler Adult Intelligence Scale third edition (WAIS-III), Rivermead Behavioural Memory Test (RBMT), Wisconsin Card Sorting Test (WCST), Auditory Verbal Learning Test (AVLT), Word Fluency Test (WFT), Trail Making Test (TMT) and Stroop Test. The full-scale IQ, as measured by the WAIS-III, was 95 (verbal IQ=95, performance IQ=95). The RBMT revealed no significant decline in memory function (standard profile score=24, screening score=12). The WFT score of 18 was significantly lower than the mean score of normal controls, which was 25. Results of the WCST, AVLT, TMT and Stroop tests were within normal ranges. Although the battery of neuropsychological tests suggested a slight decline in the patient’s cognitive function, no significant abnormalities were observed for his general function of memory.

Figure 1.

IMP-SPECT image of 3D-SSP at 2 weeks after the onset of amnesia. An area of hypoperfusion on the right ventral surface of the medial temporal lobe was observed. 3D-SSP, three-dimensional stereotactic surface projections; IMP-SPECT, N-isopropyl-[¹²³I] p-iodoamphetamine-single-photon emission CT. Global, GLB; Thalamus, THL; Cerebellum, CBL; Pons, PNS; Right lateral, RT.LAT; Left lateral, LT.LAT; Superior, SUP; Anterior, ANT; Posterior, POST; Right medial, RT.MED; Left medial, LT.MED.

The man was diagnosed as dissociative amnesia comorbid with mild depressive episode according to the Diagnostic and Statistical Manual Ⅳ-TR criteria. When he was admitted to the hospital, he had 13 points on the 17-item Hamilton Depression Rating Scale, which corresponded to mild depressive symptoms. He was able to maintain a generally stable mental state by taking 20–60 mg duloxetine, a serotonin and norepinephrine reuptake inhibitor and 0.25 mg brotizolam. He has continued taking this medication, even after recovering from amnesia.

He was discharged from the hospital after 4 months, even though his generalised amnesia continued. Due to his poor relationship with his father, he could not gain any support from his parents. Therefore, he lived in a group home and visited the hospital regularly. He engaged in occupational therapy for rehabilitation at the hospital for 6 months with the goal of getting a new job, and then started to work in a small office held by job assistants.

At 6 years and 10 months following the onset of generalise amnesia, he decided to work in another job without any job assistants. He engaged in his new job, which entailed easy work for several hours a day, without any problems. Two weeks after starting this new job, he recalled every detail of his life. He remembered that he had wanted to die when vocational training school finished and had taken an overdose on the last day of school. He stated that when he had woken up, he had lost his whole autographical and episodic memory. One week following his natural recovery from amnesia, IMP-SPECT revealed that the area of hypoperfusion on the right ventral surface of the temporal lobe had disappeared. Slight hypoperfusion in the frontal lobe was now observed (figure 2).

Figure 2.

IMP-SPECT image of 3D-SSP at 1 week after recovery from amnesia. The previously observed area of hypoperfusion on the right ventral surface of the medial temporal lobe has disappeared. 3D-SSP, three-dimensional stereotactic surface projections; IMP-SPECT, N-isopropyl-[¹²³I] p-iodoamphetamine-single photon emission CT. Global, GLB; Thalamus,THL; Cerebellum, CBL; Pons, PNS; Right latelal, RT.LAT; Left lateral, LT.LAT; Superior, SUP; Anterior, ANT; Posterior, POST; Right medial, RT.MED; Left medial, LT.MED.

Differential diagnosis

Organic disorders, such as stroke, transient ischemic attack or brain damages, were ruled out by MRI and EEG.

Treatment

Pharmacotherapy was suggested using duloxetine or a few minor tranquillisers. Psychotherapy and supportive care were provided by a psychiatrist and social workers, respectively.

Outcome and follow-up

Outcome: Recovery from generalised dissociative amnesia with restoration of perfusion on the right ventral surface of the temporal lobe. Follow-up periods: 6 years and 10 months. The patient is currently alive.

Discussion

The present case is a patient with generalised dissociative amnesia with hypoperfusion on the right ventral surface of the temporal lobe. Memory loss was attributed to psychological stress. Although amnesia lasted 6 years and 10 months, his episodic memory recovered fully when he started a new job. In addition, cerebral blood flow in the right ventral area of temporal lobe also returned to normal levels.

The most distinct feature of the present case is the reversible nature of generalised dissociative amnesia. Both memory and cerebral blood flow returned to normal, even after long-lasting total amnesia. Long-term follow-up studies are scarce,¹ and analyses of cerebral blood flow both before and after recovery from amnesia are not currently available.

Mnestic block syndrome, which may be related to altered brain metabolism, has been hypothesised to contribute to the onset of generalised dissociative amnesia.⁵ For the retrieval of episodic memory, regions of the temporofrontal junction are engaged as trigger structures for activating the cortical network. In mnestic block syndrome, there is a disconnection between the trigger structures for retrieval, and storage sites are blocked. Previously, a functional MRI analysis of a patient with dissociative amnesia revealed that the temporal area of the cortical network was not activated when stimuli related to autobiographical episodes were applied.⁶ This finding may well explain the correlation between hypoperfusion on the right ventral surface of the temporal lobe and memory loss in the present case.

With regard to psychological reasons for the observed dissociative amnesia, the loss of a job was a strong stressor for this man. The stress imparted by bankruptcy and his inability to find a job was so great as to induce generalised amnesia as an equivalent symptom to suicide. Similarly, recovery from dissociative amnesia was also related to employment. It is possible that acquiring new stable employment provided sufficient stress relief so as to alleviate suppression of his whole life’s memory. A recent study of patients with dissociative amnesia revealed that 3 out of 28 patients had stress related to a broken career.⁷

This case report has several limitations. First, we could not confirm the exact time when hypoperfusion of the temporal lobe resolved. It is possible that perfusion in the area had recovered long before recovery of dissociative amnesia. Second, we were unable to rule out malingering. During the recovery from dissociative amnesia, it is exceedingly difficult to distinguish real memory from memory learnt or obtained after the onset of dissociative amnesia.

Longitudinal naturalistic reports for generalised dissociative amnesia are exceedingly rare. It is important to confirm if dissociative amnesia and cerebral blood flow recover in parallel, even when dissociative amnesia is long-lasting.

Patient’s perspective.

When my memory was recovered, I remembered that I had wanted to die at the onset of amnesia. Although I felt slightly depressed, I could easily change my mind. I confirmed that I now lives in a different situation from that 6 years and 10 months ago.

Learning points.

• A case of generalised dissociative amnesia is presented with an area of hypoperfusion in the right ventral surface of the medial temporal lobe.

• Generalised dissociative amnesia can recover naturally, even if its duration is longer than 6 years.

• When his memory fully returned, the region of hypoperfusion on the right ventral surface of his temporal lobe also resolved.

• Eliminating the psychological conflict which precipitated the amnesia seems to be an important factor for recovery from generalised dissociative amnesia.