Amnesia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Zehra Malik, M.B.B.S[2]

Overview

Amnesia can be divided into two broad groups, retrograde amnesia and anterograde amnesia. Anterograde amnesia is the inability to form new memory and retrograde amnesia is the loss of memory prior to the onset of amnesia.

Classification

• Anterograde amnesia
• Retrograde amnesia
• Dissociative Amnesia
• Post-traumatic Amnesia
• Infantile Amnesia
• Drug-Induced Amnesia
• Amnesia in Korsakoff’s Syndrome
• Selective Amnesia
• Epileptic Amnesia
• Lacunar amnesia

Common Cause of Tremor	Differentiating Feature of Tremor	Main Feature of Disease
Essential tremor	Postural Tremor - Frequency 4–12 Hz, Bilateral onset	gait ataxia, vestibulo-cerebellar involvement, reduced by alcohol, family history, stress/fatigue can increase tremor amplitude, increases with voluntary movements
Parkinson’s disease	Resting Tremor - Unilateral onset	Bradykinesia, micrographia, stooped posture, ataxia, rigidity, imbalance, depression, apathy, decreases with voluntary movements
Physiologic Tremor	Postural tremor - High frequency 8–10 Hz, low amplitude, irregular oscillations	Tremor occurs while maintaining a posture and mostly disappears if eyes are closed or a load is placed on the muscles. Subtle innate tremor normally present in the general population.
Enhanced Physiologic Tremor	Increased amplitude	Physiologic tremor enhanced due to fatigue, sleep deprivation, drugs, endocrine disorders, caffeine, stress.
Cerebellar Tremor	Intention tremor - Low frequency <4 Hz	Occurs in multiple sclerosis, stroke, brainstem tumor, or cerebellar trauma. May feature ataxia, dysmetria, dysdiadochokinesia, and dysarthria.
Drug Induced Tremor	Can enhance rest, action, postural tremors	Amiodarone, bronchodilators, lithium, metoclopramide, neuroleptics, theophylline, valproate
Orthostatic Tremor	Essential tremor variant, high frequency 14 Hz-18 Hz	Occurs in the legs on standing and is relieved by sitting down
Holmes tremor	Combination of rest, action, and postural tremors, Frequency 2Hz-5Hz	Mostly due to vascular lesion in mesencephalic, thalamic or both regions.