Bilateral INOs and Partial 3rd Nerve Palsies

This is a 45-year-old man with progressive ptosis and ophthalmoparesis. 10 years prior to presentation, he experienced diplopia and had a hyperintense lesion involving the medial longitudinal fasciculus (MLF) per report. Over time, he developed bilateral adduction paresis, ptosis and upgaze paresis (with sparing of pupils and inferior rectus muscles) with corresponding T2/FLAIR hyperintensities involving the periaqueductal region, bilateral MLFs and paramedian midbrain in the region of the 3rd nuclei and exiting fascicles bilaterally. Convergence did not overcome his adduction deficits. Going along with bilateral MLF lesions (as opposed to myasthenia gravis, chronic progressive external ophthalmoplegia, restrictive processes or other causes of progressive ophthalmoparesis) were + head impulse tests in the planes of the posterior canals (which only travel through the MLFs), gaze-evoked nystagmus in downgaze (vertical gaze-holding pathways travel through the MLFs on their way to the interstitial nucleus of Cajal), very slow and limited adducting saccades and abducting nystagmus when looking laterally. Wall-eyed bilateral INOs and bilateral partial 3rd nerve palsies were diagnosed secondary to his bilateral rostral pons and paramedian midbrain disease, although the origin of these lesions was unclear at the time of initial consultation.