Psychology and Psychiatry: Open access
Open Access

Saccadic Intrusions: Don’t Miss Toxins & Drugs

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Saccadic intrusions are involuntary conjugate saccades (rapid eye movements) that interrupt fixation. Although, some of these may be seen in normal individuals, most of the time these are pathologic. Generally, they are almost always pathologic if they are symptomatic. They often reflect dysfunction of the brainstem, cerebellum, superior colliculus, basal ganglia, and/or cerebral hemispheres1,2. First, we have to differentiate nystagmus from saccadic intrusions. Nystagmus is classically described as rapid jerky movements followed by slow corrective saccades whereas in intrusions, the movements are purely saccadic. The next step would be to distinguish two groups of saccadic intrusions by the presence or absence of an intersaccadic interval. Saccadic intrusions with intersaccadic intervals such as square wave jerks, macro saccadic oscillations and saccadic pulses may be seen in neurodegenerative diseases and demyelinating diseases1. Saccadic intrusions without intersaccadic intervals such as ocular flutter and opsoclonus can be seen in various conditions5. This includes parainfectious brainstem encephalitis, metabolic toxic states, demyelinating diseases, inherited disorders, and paraneoplastic conditions (primarily neuroblastoma in children, and small cell lung carcinoma, breast carcinoma or ovarian carcinoma in adults), although in many cases, the cause remains unknown1,2,4. Ocular flutter and opsoclonus are rarely caused by drugs and toxins. This association has been reported in drugs/toxins such as cocaine, phenytoin, lithium, amitriptyline, phencyclidine and more recently venlafaxine.

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