Positional nystagmus is a rapid eye movement caused by body or head position, often accompanied by dizziness. It has various classifications, with the most common cause being benign paroxysmal positional vertigo (BPPV) due to tiny debris in the inner ear. Positional alcohol nystagmus (PAN) is not related to any dysfunction and is caused by alcohol absorption. PAN can be confused with horizontal gaze nystagmus (HGN), which is used as a test for alcohol or drug intoxication.
Positional nystagmus is a very rapid eye movement over which the patient has no control and is caused or influenced by body and/or head position. These rapid eye movements are usually accompanied by feelings of dizziness. There are many types of positional nystagmus differentiated by both the location causing the nystagmus and the direction of the eye movements. The most common cause of positional nystagmus is benign paroxysmal positional vertigo (BPPV). One specific type of nystagmus, positional alcohol nystagmus, is not related to any disease or dysfunction, but is concerned with the absorption of alcohol into the bloodstream.
Examples of positional nystagmus classifications include upbeat, downbeat, lateral, and directional change. Positive nystagmus is observed when the patient is lying down with the head tilted and indicates BPPV in the posterior canal of the inner ear. Bearish nystagmus is similar but occurs without head tilt and indicates BPPV in the anterior canal. Lateral positional nystagmus is seen as a side-to-side movement when the patient is lying down, but the cause of this type is less certain. Positional nystagmus that changes direction causes movements that change direction depending on whether the patient is lying down or sitting. Another variant, cervical nystagmus, is related to compression of a cervical disc on the vertebral artery.
BPPV is explained as an accumulation of tiny bits of debris sometimes called “ear rocks.” These tiny crystals are formed from calcium carbonate, similar in theory to kidney stones, and are officially known as otoconia. They slowly dissolve back into the inner ear solution so that any symptoms they cause can stop for a period of time before they come back. Most cases of BPPV are caused by head trauma or simply by aging. Some viruses and the effects of ear surgery are also known causes, but in many cases a clear cause is never determined.
Eye movements caused by positional alcohol nystagmus (PAN) are sometimes confused as signs of horizontal gaze nystagmus. Police officers use horizontal gaze nystagmus (HGN) as a test for alcohol or illegal drug intoxication. To accurately view the HGN, the subject lies on their side with their head in alignment with the spine. If the head is tilted to one side, any nystagmus seen is caused by PAN showing the presence of alcohol but not indicating a level of intoxication. A false positive for HGN can then be recorded.
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