Recognizing periodic alternating nystagmus

Abstract

Congenital or acquired periodic alternating nystagmus (PAN) is characterized by nystagmus occurring in a cycle. The cycle consists of a left-beating nystagmus, a transition phase, a right-beating nystagmus, and a further transition phase. The purpose of this review is to assist the clinician in the recognition of periodic alternating nystagmus (PAN), either as a type of congenital nystagmus or in its acquired form, and to highlight why such identification is important. Recent studies using eye movement recordings are reviewed to point out the frequency of congenital PAN in samples of patients with congenital nystagmus, and to describe the characteristics of the waveforms and the influence of foveation time on the alternation of head turns. Classical and new surgical alternatives are reported. The identification of congenital PAN is essential when surgical treatment is being considered for the correction of anomalous head postures. Acquired PAN is usually due to cerebellar disease and causes oscillopsia. Unlike other forms of acquired nystagmus, it responds well to drug treatment.

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“…Acquired PAN has a specific pattern identified by the presence of spontaneous nystagmus in the primary position, which beats horizontally in one direction for 1 or 2 minutes, followed by a quiet period, and then reappearance of the nystagmus in the opposite direction for a similar length of time. Acquired PAN can also occur in association with midbrain or cerebellar disease and as an adverse effect of medication such as lithium and anticonvulsants or from loss of vision, e.g., cataracts, vitreous hemorrhage, and optic atrophy [11][12][13][14][15][16]44]. Although the mechanism of periodic alternating nystagmus is not clearly understood, lesions of the uvula and nodules as well as structures located in the posterior vermis of the cerebellum, have been shown to be temporally related to its occurrence [45].…”

“…Infantile (a)periodic alternating nystagmus (IAPAN) has all the electrophysiological and clinical characteristics of INS except like acquired PAN the null zone shifts position in a regular (periodic) or irregular (aperiodic) pattern [11][12][13][14][15][16]44]. This results in changes in the intensity and/or direction of the nystagmus and dynamic changes in visual function and anomalous head positioning from seconds to minutes.…”

“…About 9% to 33% of patients with INS will have an inherent, rhythmic, periodic or aperiodically changing nystagmus intensity and/or direction over time. Most clinicians are familiar with this oscillation as acquired periodic alternating nystagmus (PAN) [11][12][13][14][15][16]44]. Acquired PAN has a specific pattern identified by the presence of spontaneous nystagmus in the primary position, which beats horizontally in one direction for 1 or 2 minutes, followed by a quiet period, and then reappearance of the nystagmus in the opposite direction for a similar length of time.…”

“…Most clinicians are familiar with this oscillation as acquired periodic alternating nystagmus (PAN). Acquired PAN has a specific pattern identified by the presence of spontaneous nystagmus in the primary position, which beats horizontally in one direction for 1 or 2 minutes, followed by a quiet period, and then reappearance of the nystagmus in the opposite direction for a similar length of time [15]. Acquired PAN is usually seen in association with vestibulo-cerebellar disease and neurodegenerative conditions such as Friedreich's ataxia, or vision loss [15].…”

“…Acquired PAN has a specific pattern identified by the presence of spontaneous nystagmus in the primary position, which beats horizontally in one direction for 1 or 2 minutes, followed by a quiet period, and then reappearance of the nystagmus in the opposite direction for a similar length of time [15]. Acquired PAN is usually seen in association with vestibulo-cerebellar disease and neurodegenerative conditions such as Friedreich's ataxia, or vision loss [15]. Infantile aperiodic alternating nystagmus (IAPAN) has all the characteristics of INS except that the nystagmus direction and/or intensity changes in an irregular pattern over time [16,17].…”