Amnesia Types

Snapshot

• A 55-year-old male is brought to the clinic by his wife for memory issues.  Per the wife, patient has been having difficulties recalling events that happened over the past couple of days, which included their daughter’s wedding. When asked to describe what happened yesterday, the patient began telling stories of him attending a dinner party hosted by the current president of the United States. (Korsakoff syndrome) 

Introduction

• Overview
  • condition of memory loss 
    • most commonly affects declarative/explict memories (facts or events) rather than nondeclarative/implict memories (non-conscious knowledge)
• Common causes  
  • injuries (e.g., trauma) 
  • disease (e.g., Alzheimers)
  • infections (e.g., HIV/AIDS)
  • anoxia
  • nutritional deficiencies 
• chronic alcoholism 

Retrograde Amnesia

• Overview
  • loss of memory-access to events that occurred or information that was learned in the past, before CNS insult
  • commonly affects episodic, autobiographical, and declarative memory with sparing of procedural memory
• Pathogenesis
  • commonly results from damage to regions of the brain associated with episodic and/or declarative memory
    • hippocampus
    • diencephalon
• temporal lobes

Anterograde Amnesia

• Overview
  • loss of the ability to create new memories after CNS insult
  • long-term memories are intact while ability to recall the recent past is affected
• Pathogenesis
  • most well-described regions affected are the medial temporal lobe, basal forebrain, and fornix
  • common causes include    
    • benzodiazepine
    • encephalitis
    • traumatic brain injury
    • alcohol intoxication 

Transient Global Amnesia

• Overview
  • acute onset anterograde amnesia that resolves within 24 hours
  • no other focal neurological signs or symptoms
  • often linked to trigger (e.g., Valsalva maneuver, sympathetic activation, etc.)
• Pathogenesis
  • most likely due to hippocampal injury, but not clear
    • arterial ischemia
• venous congestion 

Korsakoff Syndrome 

• Overview 
  • amnestic disorder secondary to thiamine (vitamin B1) deficiency caused by prolonged alcohol abuse 
  • characterized by anterograde > retrograde amnesia, confabulation, lack of insight, and apathy 
    • confabulation describes invented memories that fill in gaps in memory 
• Pathogenesis
  • signficant thiamine deficiency leads to damage to the medial thalamus and mammillary bodies  
• these brain regions are parts of the limbic system, which are involved in emotion and memory 

Dissociative Amnesia 

• Overview    
  • memory disorder characterized by sudden retrograde episodic memory loss, often involving personal information 
  • can be associated with dissociative fugues (abrupt travel or wandering during a period of dissociative amnesia, associated with traumatic circumstances) 
• Pathogenesis
  • thought to be functional and no associated with any brain trauma or disease
  • thought to occur as a result to extreme psychological trigger/stress