Periodic Alternating Nystagmus

Timothy C. Hain, MD • Page last modified: May 1, 2021

Supplemental material : Video of congenital nystagmus, periodic variant

Supplemental material : Video of acquired PAN (periodic alternating nystagmus)

Periodic alternating nystagmus in person who had a previous hemorrhage into nodulus of cerebellum.

PAN is a persistent horizontal jerk nystagmus that periodically changes direction.

Acquired PAN.

PAN can be divided into congenital and acquired. Acquired PAN is of the most interest. The acquired type is further subdivided into those due to cerebellar problems, visual problems, and idiopathic.

One of the PAN movies on this site shows a person with strong acquired PAN, with a long period (about 4 minutes), of uncertain cause (idiopathic).

A discussion of our group's research on PAN is found here.

Acquired PAN associated with cerebellar disturbances:

An example of strong acquired PAN is shown in the figure above. This person acquired PAN through a stroke to the cerebellum.

Acquired PAN has been mainly reported in cerebellar disorders. Cerebellar disorders associated with PAN include arachnoid cyst of the posterior fossa (Towle and Romanul 1970) , Arnold-Chiari malformation (Meienberg and Hoyt 1980) , spinocerebellar degeneration (Plant 1982; Stell, Bronstein et al. 1989; Yabe, Sasaki et al. 1998; Yabe, Sasaki et al. 1998) , focal cerebellar lesions associated with multiple sclerosis (Keane 1974) , and cysticercosis (Keane 1993) . PAN can occur as a side effect of anticonvulsant medication (Campbell 1980) , presumably also related to cerebellar dysfunction.

There is substantial evidence that PAN can be the result of damage to the cerebellar uvula and nodulus. For example, PAN can be induced in monkeys by lesions of nodulus (Waespe, Cohen et al. 1985; Wearne, Raphan et al. 1998) . In humans, while many reports of PAN are associated with diffuse cerebellar lesions, some have been associated with small specific lesions of the nodulus. Kennard et. al. reported a case of PAN in a patient with cerebellar medulloblastoma, which is a tumor that arises in the cerebellar nodulus (Kennard, Barger et al. 1981). In our case (Chiu and Hain, 2002), we hypothesized that the nodulus or uvula might have been damaged early in life, thus resulting in an enlarged cisterna magna and a tendency towards PAN. Recently it has been reported that PAN can be provoked by lithium (Lee and Lessell, 2003). This is unsurprising as lithium toxicity can induce other types of central nystagmus and is also a cerebellar toxin. It seems likely that other disorders that affect vision or cerebellar function may also be associated with PAN in the future.

Acquired PAN from visual disturbances

PAN can also be associated with visual disturbances such as cataract, which can clear after surgery with vision improvement (Cross, Smith et al. 1982; Jay, Williams et al. 1985) . This suggests that PAN can be a transient consequence of sensory impairment. Theoretical analyses of PAN postulate that it is related to loss of central inhibition of vestibular circuitry (Leigh, Robinson et al. 1981; Furman, Hain et al. 1989; Furman, Wall et al. 1990) . These models have triggered PAN with vestibular signals. In our patient, we hypothesize that a Meniere's attack may have provided the trigger for PAN in a similar fashion as visual loss may also induce PAN.

Congenital PAN.

Congenital PAN is mainly found in albinism (Guyer and Lessell 1986; Abadi and Pascal 1994). A movie of congenital PAN can be accessed here. This nystagmus has the increasing-velocity exponential, and also often is much more rapid to change direction than the acquired PAN.

Normal PAN ?

The author has observed that some normal persons appear to have minor amounts of PAN. In order to record this, one must use a sensitive method (i.e. IR) and record for several minutes.

Peripheral PAN ?

There are several reports of PAN occurring in individuals with Meniere's disease, e.g. Murofushi et al, 2008 and Chiu and Hain, 2002. We think that these are all individuals with cerebellar disturbances and Meniere's together. We do not think there is truly a "peripheral" PAN. Otherwise, one would need to rethink the definition of Meniere's and include disorders that are outside of the inner ear.


Both congenital and acquired PAN can often be abolished by treatment with Baclofen (Halmagyi, Rudge et al. 1980; Troost, Janton et al. 1990) .

PAN CASE REPORT (Chiu, 2002).

A 51 year-old Caucasian male with a history of decreased hearing in left ear and recurrent vertigo over 10 years attributed to Meniere's disease presented to our hospital for two drop attacks. The drop attacks were not associated with headache, dizziness, vertigo, loss of consciousness, confusion, visual changes, nausea, vomiting, or chest pain, and they were attributed to the "otolithic crises of Tumarkin", which are found in advanced Meniere's disease .

While in the hospital, he developed an episode of vertigo with nausea and vomiting. His eyes at that time also showed strong horizontal nystagmus which were reported one reliable observers as being left beating, and by another as being right beating.

Electronystagmography showed an alternating right and left beating nystagmus with a periodicity of approximately 50 seconds consistent with PAN. Clinical exam at that time using Frenzel's goggles also documented PAN. He was treated with baclofen. The nystagmus abated, and on repeat exam using Frenzel's goggles 1 month later, it was not evident.

Figure 2: MRI of case of PAN showing enlarged cisterna magna.

As shown in figure 2, a magnetic resonance scan (MRI) of the brain without contrast demonstrated an enlarged cisterna magna associated with mild hypoplasia of right cerebellar hemisphere. A subsequent cisternogram demonstrated communication of the enlarged posterior fossa space with cerebral spinal fluid, documenting that the apparently enlarged cisterna magna was not a subarachnoid cyst.

This clinical report illustrates that the finding of an enlarged cisterna magna can be associated with a pathological abnormality, namely PAN. It further suggests that in susceptible individuals, PAN may be transiently induced by vestibular imbalance.