What are the fourth cranial nerve nuclear and fascicular lesions in multiple sclerosis (MS)?

Updated: Feb 21, 2019
  • Author: Fiona Costello, MD, FRCP; Chief Editor: Hampton Roy, Sr, MD  more...
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The trochlear or fourth nucleus lies below the oculomotor nucleus, dorsal to the MLF, at the level of the inferior colliculus. [42] A lesion of the fourth nerve nucleus or proximal fascicle causes hyperdeviation (elevation) of the contralateral eye. [40] The hyperdeviation of a fourth nerve palsy is greatest in contralateral gaze and is exacerbated by ipsilateral head tilt. A head tilt opposite the side of the higher or hyperdeviated eye tends to alleviate some symptoms. In patients with MS, a demyelinating lesion may cause combined INO and contralateral fourth nerve palsy because of the anatomic proximity of the MLF and the fourth nerve nucleus and fascicle. [40] A trochlear nerve palsy may be difficult to distinguish from a skew deviation when the magnitude of hypertropia increases with ipsilateral head tilt.

In 2010, Wong [45] proposed the “upright-supine test” to differentiate skew deviation from trochlear nerve palsy. During this clinical test, a near target is held one third of a meter in front of the patient, in both the upright and supine positions. The examiner looks for a vertical deviation that decreases by 50% or more from the upright to supine position, suggesting skew deviation. [45] Alternatively, if the upright-supine test finding is negative and the vertical deviation decreases by less than 50% from the upright to supine position, the vertical strabismus is likely caused by a fourth nerve palsy. [45]


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