Isolated Central 4th Nerve Palsy

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 40-year-old man with a right hypertropia that worsened in left and down gaze in addition to right head tilt, and improved in left head tilt. There was subjective excyclotorsion OD with double Maddox rod testing. This was consistent with a right 4th nerve palsy. He had a known left midbrain cavernoma which had bled several years prior to this evaluation making the localization of his 4th nerve palsy "central". Given the proximity of the left 4th nucleus and its fascicle to the left medial longitudinal fasciculus (MLF) and oculosympathetic tract, when a left internuclear ophthalmoplegia (INO) and/or left Horner's syndrome, respectively, is seen with a right (CONTRALATERAL) 4th nerve palsy, a "central" 4th is strongly suggested relating to the decussating course of the 4th nerve (see https://collections.lib.utah.edu/details?id=1260008). However, an isolated 4th nerve palsy can also be central and related to nuclear and/or fascicular injury, as in this case. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This patient had a right hypertropia that worsened in left and down gaze in addition to right head tilt, and improved in left head tilt. There was subjective excyclotorsion OD with double Maddox rod testing. This was consistent with a right 4th nerve palsy. He had experienced a left midbrain hemorrhage which had bled several years prior to this evaluation making the localization of his 4th nerve palsy "central". Given the proximity of the left 4th nucleus and its fascicle to the left medial longitudinal fasciculus (MLF) and oculosympathetic tract, when a left internuclear ophthalmoplegia (INO) and/or left Horner's syndrome, respectively, is seen with a right (CONTRALATERAL) 4th nerve palsy, a ‘central' 4th NP is strongly suggested relating to the decussating course of the 4th nerve. However, an isolated 4th NP can also be central and related to nuclear and/or fascicular injury, and will be contralesional as in this case. (Video and legend created with the assistance of Dr. Kemar Green) https://collections. lib.utah.edu/ark:/87278/s6hf1tbf