8282ournal ofNeurology, Neurosurgery, and Psychiatry 1997;62:82-84 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.62.1.82 on 1 January 1997. Downloaded from SHORT REPORT Post-traumatic stress disorder and head injury as a dual diagnosis: "islands" of memory as a mechanism Nigel S King Abstract A third factor is the interpretation of any This case study describes post-traumatic amnesia for the event. A lack of full memory stress disorder (PTSD) and head injury for the traumatic event can be due to organic after a road traffic accident involving a amnesia and thus a sign of head injury or due to pedestrian. Previous studies have pro- psychogenic amnesia and thus a potential posed two mechanisms by which this dual PTSD symptom of avoidance. No agreed diagnosis may occur: (1) when post-trau- method of distinguishing between these types matic amnesia and retrograde amnesia of amnesia has been reported. It seems rea- are small or non-existent and (2) when sonable, however, that if psychogenic amnesia non-declarative memory systems for the in PTSD is primarily an avoidance or dissocia- traumatic event are in operation. This tive reaction then it is more likely to occur for case study demonstrates a third mecha- aspects of the event which are perceived as nism-"islands" of memory within post- being the most traumatic rather than for those traumatic amnesia. that are perceived as less so. It is no doubt possible, however, for an investigator to (J Neurol Neurosurg Psychiatry 1997;62:82-84) attribute amnesic aspects of post-traumatic amnesia to PTSD or vice versa. Two mechanisms by which both a head Keywords: post-traumatic stress disorder; head injury; injury and PTSD can occur have been high- "islands" of memory lighted: (1) when retrograde amnesia or post-trau- It is clear that circumstances in which a person matic amnesia is very small or non-existent. In sustains a head injury (for example, assaults, such cases memories of a traumatic incident road traffic accidents, industrial accidents) immediately before or immediately after the may often be those where "threatened death or head injury may be present.7 http://jnnp.bmj.com/ serious injury" (DSM IV)' also occurs2 and (2) Contemporary memory theory posits the therefore where post-traumatic stress disorder existence of multiple and independent mem- (PTSD) might also be expected. The dual ory systems. These include the declarative or diagnosis of PTSD and head injury, however, is explicit system (stored experience actually or uncommon, particularly if judged by the num- potentially accessible to conscious recollec- ber of published examples of its occurrence.36 tion) and the non-declarative or implicit sys- due to several factors. tem experience not accessible to This is probably Firstly, (stored on September 30, 2021 by guest. Protected copyright. organic amnesia which commonly accompa- consciousness).8 Within such theories the re- nies head injury (in the form of unconscious- experiencing of a traumatic event may be via ness, post-traumatic amnesia, or retrograde "intense psychological distress on exposure to amnesia), is thought to protect most patients internal or external cues that symbolise or with head injury from developing PTSD. resemble an aspect of the traumatic event" Indeed, some writers have used rigid defini- (DSM IV) without conscious recall of the tions of PTSD and head injury to argue that event itself.5 "PTSD and MTBI (mild traumatic brain This paper presents a case study which injury) are mutually incompatible since highlights a third mechanism by which head patients who sustain PTSD simply cannot injury and PTSD can co-occur-"islands" of 'forget' the traumatic event, whereas patients memory during post-traumatic amnesia. Post- who sustain MTBI (for example, cerebral con- traumatic amnesia is usually defined as the have no recollection of the traumatic period of time between receiving a head injury Clinical Psychology cussion) Department, event. "7 and the resumption of normal continuous Rivermead A second factor can be the existence of memory.9 11 "Islands" of memory or recollec- Rehabilitation Centre, postconcussion symptoms. Some postconcus- tions of events which occur outside continuous Abingdon Road, Oxford OXI 4XD, UK sion symptoms are identical with some PTSD memory for events are a common feature of N S King symptoms- for example, poor concentration, post-traumatic amnesia1° 12 and occur in at Received 15 April 1996 depression, anxiety, sleep disturbance, and least a third of all cases of mild head injury. 13 and in revised form at In Gronwall and Wrightson's sample "islands" 17 July 1996 irritability and could, theoretically least, Accepted 13 August 1996 cause a misdiagnosis of PTSD. of memory were usually reported for specific Post-traumatic stress disorder and head injury as a dual diagnosis: "islands" ofmemory as a mechanism 83 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.62.1.82 on 1 January 1997. Downloaded from changes in events-for example, being helped "island" of memory, sweaty palms, and signifi- into an ambulance, being discharged from cantly increased heart rate and arousal levels hospital etc. Forty four per cent of those who when near most roads, phobic avoidance of all reported "islands" had them for events less but minor roads, persistent efforts to avoid than five minutes after injury and 71% thoughts and conversations about the acci- reported them for events less than 15 minutes dent, very diminished participation in activi- after injury. ties (for example, staying in his bedroom for up to three days consecutively), feelings of detachment from others (particularly family Case report members), sleeping for only about 25% of the A 21 year old unemployed man sustained a time before the accident, irritability and verbal head injury as the result of being hit by a car outbursts of anger, difficulties concentrating from behind as a pedestrian while hitch hiking as highlighted by being able to read only one home at night. He also had considerable or two pages of a book before losing concen- orthopaedic injuries. He had no previous his- tration (compared with reading a book every tory of head injury, psychiatric treatment, or few days before the injury), exaggerated startle psychological trauma, but reported being an response, hypersensitivity to most potential occasional cannabis user. dangers inside and outside his house, and Evidence for head injury included the fol- impairment in social functioning (in the form lowing: of drinking to excess, much diminished inter- (1) Ambulance records which stated that (a) est in socialising with friends, and phobic he was "probably knocked out for a few min- avoidance of busy roads). utes according to witness"; (b) he was struck at The criteria for fulfilling the diagnosis of about 40 mph and was thrown on to the bon- PTSD was confirmed by scores on the PTSD net of the car, smashing the windshield symptom scale.'4 (almost certainly with his head); (c) he had a wound to the front of his head and significant pain at the back of the head; and (d) he had Discussion neck injuries that required a collar. This case study presents someone with both a (2) Hospital records on admission diagnosed head injury and PTSD arising from the same (a) mild head injury and recommended hourly event. A key feature of the PTSD was the re- neurological observations; (b) boggy haem- experiencing of intrusive images, thoughts, atoma over the left temporoparietal area; (c) and nightmares of an "island" of memory dur- left frontal skull laceration; and (d) laceration ing post-traumatic amnesia after the head to the chin. injury. The case therefore infers a third mecha- (3) Medical discharge summary included the nism by which the dual diagnosis of head diagnosis of head injury. injury and PTSD may occur. An "island" of (4) At a routine follow up nine days after memory for part of the traumatic event can be injury post-traumatic amnesia was established responsible for the recurrent intrusive recollec- by retrospective questioning. He described a tions of the trauma which are a key feature of single memory immediately after his head the diagnosis of PTSD (DSM IV). This mech- injury, of lying in the road, seeing the car that anism is consistent with previous explanations http://jnnp.bmj.com/ had hit him turn around, and him having great of "islands" of memory which consider them difficulties in pulling himself to the side of the to happen only when a strong "stimulus" road due to his orthopaedic injuries. The occurs during partial recovery from a head intensely traumatic aspect of this memory was injury.'3 15 Gronwall and Wrightson'3 postu- the mistaken perception that the car had lated that the process of recovery after concus- intentionally hit him and that it had turned sion may occur in two phases. The initial round to "finish him off". He had no other phase often occurs during the first hour after on September 30, 2021 by guest. Protected copyright. memories until 2j days later on the trauma mild head injury and the second phase then ward in hospital. Normal memory resumed follows. They argue that "islands" of memory almost immediately after this time. Post-trau- usually occur during the first phase and only matic amnesia was thus assessed as 24 days. "when a stimulating event coincides with a (5) At the follow up interview he reported peak arousal, providing enough external acti- pronounced postconcussion symptoms, which vation to push the peak above the threshold included sensitivity to light, headaches, con- level for memory".'3 An explanation of the centration difficulties, forgetfulness, dizziness, patient's "island" of memory is thus that the sleep disturbance, irritability, depression, feel- notable heightened state of arousal present ings of frustration, and restlessness.