From the Guidelines
Square wave jerks are a normal finding when they occur occasionally, but become pathological when frequent or large in amplitude, and their presence should prompt neurological evaluation to identify potential cerebellar or brainstem pathology, as they can be an early sign of neurodegenerative disorders. When considering the management of conditions that may be associated with square wave jerks, such as REM sleep behavior disorder (RBD), it is essential to prioritize the patient's quality of life and morbidity, as highlighted in the American Academy of Sleep Medicine clinical practice guideline 1. Some key points to consider in the context of square wave jerks include:
- They are characterized by brief, involuntary eye movements, typically measuring 0.5-5 degrees in amplitude and occurring at a frequency of 1-2 Hz
- They can be associated with cerebellar disorders, particularly involving the vermis, and conditions like progressive supranuclear palsy, multiple system atrophy, spinocerebellar ataxias, and certain medications
- Diagnosis is typically made through clinical observation and confirmed with eye movement recordings
- Treatment focuses on addressing the underlying cause rather than the eye movements themselves, and in most cases, no specific treatment is needed for the square wave jerks unless they are severely affecting vision or quality of life, as seen in the management of RBD 1. In clinical practice, it is crucial to prioritize the patient's morbidity, mortality, and quality of life when evaluating and managing square wave jerks, and to consider the potential underlying causes and associated conditions, such as RBD, as discussed in the American Academy of Sleep Medicine clinical practice guideline 1.
From the Research
Definition and Characteristics of Square Wave Jerks
- Square wave jerks (SWJ) are saccadic eye movements that interrupt fixation, characterized by an initial saccade that moves the fovea away from the intended position of fixation, followed by a second saccade in the opposite direction, which refoveates the fixation position 2.
- SWJ are the most common saccadic intrusion, which can be readily seen at the bedside and also quantified using oculographic techniques 3.
- They are involuntary, horizontal, saccadic intrusions that occur in 24-60% of healthy adults, with a high prevalence also found in children and adolescents 2.
Clinical Significance of Square Wave Jerks
- SWJ can be a potential indicator for various clinical conditions, including neurological, neuropsychiatric, and psychiatric disorders 3.
- They are particularly important for clinicians because they can be readily observed at the bedside, and their presence may suggest underlying pathological conditions 3.
- SWJ have been found to occur in patients with movement disorders, such as parkinsonism, ataxia, dystonia, myoclonus, tremor, and chorea, and can provide important information for differential diagnosis 4.
Neural Mechanism and Localization
- The neural mechanism for the production of SWJ is not fully understood, but it is thought to involve the brainstem and the frontal eye field, among other areas 5, 6.
- SWJ may be related to fixation instability and central neurological lesions, but they can also occur in the absence of any apparent neurological pathology 5.
- The study of SWJ and other eye movements can provide valuable insights into the localization and type of diseases affecting the brain, particularly those involving the pons and other brainstem structures 6.