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This 70 year old man reports that he has been falling more lately. His partner tells you that the falls are often backward and seem to occur unexpectedly.
A likely cause of this abnormality is:
Incorrect
Correct! These are square wave jerks, in which the eyes make conjugate saccades to one side of
fixation, and then, after a very brief stationary (“inter saccadic”) interval, move back to fixate straight ahead.
These eye movements do not constitute nystagmus, which is defined as involuntary rhythmic oscillations initiated by a slow drift of the eyes. There is no slow drift here. The oscillations begin with saccades and end with saccades. Called “saccadic intrusions,” they represent lack of inhibition of the brainstem saccadic generators.
Square wave jerks occur most commonly in progressive supranuclear palsy (PSP), but also in severe brainstem trauma, and in many other disorders that affect the brainstem. They do not usually cause blurred vision or other symptoms because vision is suppressed during saccades. Often overlooked by examiners, square wave jerks are an important clue that PSP is the cause of a parkinsonian state. Although patients with PSP often display axial rigidity and frequent falls, they lack the typical clinical features of Parkinson disease.
With regard to the other answer choices: square wave jerks occur much less frequently in Parkinson disease than in PSP. Ataxia is more prominent than square wave jerks in paraneoplastic cerebellar degeneration and hereditary cerebellar ataxias.
These eye movements do not constitute nystagmus, which is defined as involuntary rhythmic oscillations initiated by a slow drift of the eyes. There is no slow drift here. The oscillations begin with saccades and end with saccades. Called “saccadic intrusions,” they represent lack of inhibition of the brainstem saccadic generators.
Square wave jerks occur most commonly in progressive supranuclear palsy (PSP), but also in severe brainstem trauma, and in many other disorders that affect the brainstem. They do not usually cause blurred vision or other symptoms because vision is suppressed during saccades. Often overlooked by examiners, square wave jerks are an important clue that PSP is the cause of a parkinsonian state. Although patients with PSP often display axial rigidity and frequent falls, they lack the typical clinical features of Parkinson disease.
With regard to the other answer choices: square wave jerks occur much less frequently in Parkinson disease than in PSP. Ataxia is more prominent than square wave jerks in paraneoplastic cerebellar degeneration and hereditary cerebellar ataxias.
Incorrect