Test Your Knowledge - Bilateral 4th Nerve Palsies

Watch the video until instructed to stop. Which of the following features is likely to be present given her exam findings? A. Gaze-evoked nystagmus and impaired smooth pursuit B. History of traumatic brain injury C. History of blepharoplasty or brow lift surgery and prominence of superior sulcus on exam D. Absence of hypertropia with head tilt. A. Incorrect. These additional ocular motor features of cerebellar dysfunction would not be expected in this case. The more common pattern of the "alternating skew" associated with cerebellar disorders is a hypertropia of the abducting eye - e.g., right hypertropia in right gaze and left hypertropia in left gaze. Since an alternating skew is usually related to flocculus/paraflocculus dysfunction, gaze-evoked nystagmus, spontaneous downbeat nystagmus, and impaired smooth pursuit are also commonly seen. Divergence insufficiency is another ocular motor condition that may relate to flocculus/paraflocculus pathology, and while the esotropia may increase slightly in downgaze, esotropia should be seen in primary gaze as well. Cerebellar disease would also not explain excycloduction in both eyes. B. Correct. Bilateral 4th nerve palsies would present with this pattern of hypertropia of the adducting eye since the superior oblique muscle has its greatest vertical action in adduction (due to the vector of the superior oblique muscle after passing through the trochlea). A right 4th nerve palsy would cause a right hypertropia worse in left gaze, while a left 4th nerve palsy would cause a left hypertropia worse in right gaze. If bilateral 4th nerve palsies are symmetric, there may be little to no hyperdeviation in primary gaze. In addition, the primary action of the superior oblique is incycloduction, so excycloduction will be seen in both eyes with bilateral 4ths. Since the tertiary action of the superior oblique (SO) muscle is abduction, an esotropia in downgaze (because the SO is also a depressor) in a V-pattern will be seen with bilateral 4ths. Trauma is the most common cause of bilateral 4th nerve palsies. C. Incorrect. These features are associated with sagging eye syndrome. Asymmetric or unilateral sagging eye syndrome may present with a relative hypertropia of the adducting eye due to the change in the vector of the lateral rectus. In contrast to a unilateral fourth nerve palsy where the hypertropic eye is excycloducted, in asymmetric sagging eye syndrome, the hypotropic eye is excycloducted. When sagging eye syndrome is symmetric, there is divergence insufficiency (esotropia more at distance due to bilateral lateral rectus mechanical weakness), although alignment is vertically comitant. In these patients other degenerative changes of the orbital tissues are often seen, including age related ptosis related to levator dehiscence and prominence of the superior sulcus. D. Incorrect. With bilateral superior oblique paresis as in this patient, head tilt to either side will induce a significant hypertropia - e.g., right hypertropia in right head tilt due to right 4th and left hypertropia in left head tilt due to left 4th nerve palsy (not shown in the video, but was seen on the patient's exam). There is usually little to no hypertropia with head tilt in patients with congenital V-pattern strabismus, although they may have a hypertropia of the adducting eye and excycloduction secondary to relative overaction of the inferior oblique (similar to bilateral 4th nerve palsies). In cases of primary inferior oblique overaction, alignment is normal or near normal in primary and downgaze, while upgaze elicits an exodeviation. In bilateral fourth nerve palsies, as in our patient, there is an esotropia in downgaze that is significantly less or absent in primary and upgaze. Summary: This is a patient who developed bilateral fourth nerve palsies following a shunt revision for hydrocephalus. Key features of bilateral 4th nerve palsies include: alternating hypertropia with right hyper in left gaze with left hyper in right gaze, and right hyper in right head tilt with left hyper in left head tilt; V-pattern esotropia; excycloduction in both eyes.