Case of transient global amnesia-like syndrome after recreational cold-water swimming

Background

In 1801, Dr James Currie described the beneficial effects of cold water immersion in the treatment of typhus fever in his work entitled ‘Dr. Currie on the Affusion of Cold Water’.1 Currie ‘stripped him [the afflicted individual] naked and threw four or five gallons of sea water on him, dried him and put him to bed’. When the fever returned, he repeated the procedure; ‘I threw water again over him with the same happy effect’. He likely recognised the phenomenon of after drop where core temperature can further reduce on exiting the water.2 Now 221 years later, immersion in cold water is undergoing somewhat of a revival as a recreational activity in the form of cold-water swimming.3 Enthusiasts swim in bodies of water that range from small artificial lakes to oceans, proclaiming benefits to mental and physical health in addition to overall well-being, beyond that of simply swimming.4 Despite these benefits the possibility of hypothermia is a risk, particularly where water temperature is extremely low, where immersion is prolonged or where the swimmer’s physiology is unable to compensate and adapt. We describe a case of prolonged but self-limiting neurological dysfunction following a session of open water swimming, manifesting as a transient global amnesia (TGA)-like syndrome.

Case presentation

A woman in her 70s was brought to the emergency department (ED) via ambulance with acute confusion and hypothermia (34°C) after an organised session of open water swimming in a purposely flooded ex-quarry. She was normally well with no active co-morbidities and had regularly swam in open water for the past few months. On this occasion, she attended a supervised class (water temperature: 13°C) wearing a wetsuit and was seen to have left the class prematurely after 30 min. She was found shortly afterwards hyperventilating, shivering and acutely confused. First aiders reported she was not oriented to time or place and there were concerns from bystanders that she had mild right-sided weakness of her arm and face. It was not possible to ascertain the exact nature and duration of these symptoms as a collateral history could not be obtained. There was no loss of consciousness or loss of personal identity. She had no signs of physical injury. Her medical history composed of poliomyelitis as a child (with no sequelae) and a Holmes-Adie pupil resulting from a viral infection 20 years prior. She took no regular medications. She was a non-smoker and drank three units of alcohol a week. She was fully independent.

Paramedics attended by which point there was no sign of the mild weakness. She was conveyed to the ED and on arrival her temperature was 34°C, as measured with a tympanic temperature probe. The remainder of her observations were within normal limits and with external active rewarming her temperature increased to 36.4°C. Despite successful rewarming, she remained confused and this was predominantly amnestic where she was unable to recall any events since that morning and her content of speech was repetitive. This was, therefore, suggestive of anterograde amnesia with retrograde amnesia for the immediate past. There was no suggestion of specific dysphasia of speech or word generation and there were no other neurological symptoms noted from admission to the ED. On examination, her cardiovascular and respiratory systems were normal. Her pupils were 5 mm, with the right pupil sluggish to respond to light. Her cranial nerve, upper and lower limb examinations were normal with no deficit in power, tone, co-ordination or sensation. She scored 4/10 on Abbreviated Mental Test (AMT-10) and 6/12 on the 4 'A’s Test (4AT).

Investigations

A 12-lead ECG indicated left axis deviation with a complete right bundle branch block, as well as T-wave inversion in leads V5 and V6, in sinus rhythm. In the absence of chest pain and using previous ECG for comparison, no further immediate management was deemed necessary. A chest radiograph indicated normal appearances of the heart and lungs. Blood tests were reassuring with a normal white cell count (9.8×10⁹/L), haemoglobin (144 g/L) and normal biochemistry (including a sodium of 141 mmol/L). A random glucose was 6.8 mmol/L and a venous blood gas demonstrated a pH of 7.378, a pCO₂ of 5.91 kPa and a lactate of 1.53 mmol/L. CT imaging of the patient’s brain demonstrated no intracranial haemorrhage or space occupying lesion with minimal small vessel ischaemic change. An MRI of the brain with diffusion weighted imaging was subsequently performed (figure 1) indicating no restriction of diffusion or haemorrhage but again suggesting a mild degree of small vessel vascular change.

Differential diagnosis

In the context of acute confusion and anterograde amnesia following cold-water swimming, a working diagnosis of TGA was made but it was recognised that in light of the history of possible right-sided weakness, an acute ischaemic stroke needed to be excluded. The history of having been swimming in cold water yielded further consideration of watershed infarcts having occurred secondary to fluid shifts. Therefore, the MRI brain imaging was expedited to identify cerebral ischaemia. The differentials, also considered, included a prolonged postictal state from an unwitnessed focal seizure, toxic encephalopathy, migrainous process (the patient had a history of typical migraines around the menopause 10 years prior) or concussion following an unwitnessed head injury. Exercise-induced hyponatraemia is another consideration,5 although in this case serum sodium was demonstrated to be normal. Focal seizure was also felt unlikely given the hypothermia and history, and an electroencephalogram (EEG) was not performed.

A diagnosis of exclusion, TGA secondary to hypothermia was deemed the most likely causative mechanism underlying the patient’s presentation initially. The possibility of neurological deficit in the form of weakness warranted consideration but was never professionally witnessed or elicited and therefore was challenging to corroborate. The possibility that the patient had suffered from an ischaemic event even with normal MRI findings could not be entirely excluded. However, the clinical picture of amnesia in isolation occurring following cold water immersion, TGA remained the most likely diagnosis at this time.

Treatment

Initial treatment involved passive rewarming with warm clothes and a hot drink, as well as external active rewarming with a Bair Hugger and electric blankets. She was admitted under the medical team recognising the risk of ‘after drop’ where body temperature continues to drop due to central return of cool peripheral blood.

Once cerebral haemorrhage had been excluded with the CT head, she was initially treated with a single dose of 300 mg aspirin while awaiting the MRI scan. The normal MRI scan made an ischaemic event less likely and the specialist stroke team agreed with the working diagnosis of TGA. Aspirin (75 mg daily) was commenced in case of transient ischaemic attack (TIA). A formal stroke work-up was not undertaken given the low probability of a preventable cause of stroke with the cold water being the precipitating factor. The mainstay of treatment for TGA is supportive, so the patient was monitored in hospital, including repeated cognitive testing and with neurological observations, until the symptoms of confusion and amnesia resolved.

Outcome and follow-up

The patient spent 2 days in hospital, for which approximately 30 hours she remained amnestic and unable to recall the events leading up to or including the swim. Over this period, however, she gradually became oriented to time, person and place and a Mini-ACE (addenbrooke's cognitive assessment) assessment performed prior to discharge gave a result of 30/30. The patient did not, at any point, recover the memories of the day of the event. She was discharged back home. The final diagnosis was a TGA-like syndrome (given the duration of >24 hours amnesia) with antiplatelet cover being initiated given the possibility that a subtle vascular event had occurred not visible on imaging. Counselling was provided on the risks of open water swimming and performing this safely. At 18 months, she still is unable to recall the events of the day in question and now tends to enjoy swimming in heated environments.