Alternating skew on lateral gaze (Bilateral abducting hypertropia)

Abstract

We report thirty-three patients with alternating skew deviation on lateral gaze. The right eye was hypertropic in right gaze, and the left eye was hypertropic in left gaze. Most patients had associated downbeat nystagmus and ataxia and were diagnosed as having lesions of the cerebellar pathways or the cervicomedullary junction. This contrasts with a previous report in which alternating skew was seen mainly in lesions of the midbrain pretectum.

Understanding skew deviation and a new clinical test to differentiate it from trochlear nerve palsy

“…[1][2][3][4] Skew deviation is often the initial manifestation of diseases that affect the brainstem, cerebellum, or peripheral vestibular system. [4][5][6][7][8][9][10] Because both skew deviation and trochlear nerve palsy may result from intracranial lesions or trauma, and because some skew deviations may clinically mimic trochlear nerve palsy, differentiating these 2 conditions can be challenging. Understanding skew deviation remains difficult, partly because it requires knowledge of the underlying anatomy and pathophysiology.…”

“…17 In contrast, the vertical misalignment in skew deviation does not follow any set patterns; it may be comitant or incomitant, or it may even alternate with gaze direction. 7,14,18 Some skew deviations are known to mimic trochlear nerve palsy during the 3-step test-the magnitude of hypertropia in skew deviation may increase with ipsilateral head tilt; however, it may also increase with contralateral head tilt, or it may not change with head tilt at all. 19,20 Conversely, trochlear nerve palsy with spread of comitance may simulate a comitant skew deviation because in both conditions the head is usually tilted contralateral to the side of the hypertropic eye.…”

“…Others 5-7 have attributed skew deviation to cerebellar damage from surgery 5,13 or cerebellar diseases on the basis of clinical findings. 6,7,13 In most cases, [5][6][7]13,14,18,37 however, brainstem involvement had not been excluded by either neuroimaging or pathological correlation. To document that a discrete lesion in the cerebellum alone can cause skew deviation, we described in detail the clinical course of 5 patients with skew deviation caused by focal cerebellar lesions.…”

Alternating Skew Deviation due to Hemorrhage in the Cerebellar Vermis

“…Alternating skew deviation (ASD) is a subtype of skew deviation with a frequency of 12% (3), in which the side of the higher eye changes depending upon whether the gaze is directed to the left or to the right side (2)(3)(4)(5)(6). In ASD, the abducting eye is commonly hypertropic (2)(3)(4)(5)(6), which may be produced by a relative inferior rectus muscle weakness (4) or overactive superior oblique muscle (5).…”

The cerebellum in eye movement control: nystagmus, coordinate frames and disconjugacy

“…In turn, the brain generates a 'rabbit-like' lateral-eyed response, resulting in a skew deviation that alternates sense with right vs left lateral gaze. 22,23 Other theories are possible 24 and even normal human beings may develop a pattern of alternating skew deviation after prolonged monocular viewing. 25 We also note that normal humans have some cyclovergence during low frequency, vertical translation (which could be misinterpreted as fore and aft tilt), much as normal humans have some conjugate torsion during low-frequency, and interaural translation (which could be misinterpreted as a lateral tilt).…”