Case of the week 53.html

The oculomotor nerve supplies motor innervation to the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris muscles and parasympathetic innervation by way of the ciliary ganglion to the pupillary constrictor and the ciliary muscles.
Lesions of the oculomotor nucleus are most often caused by ischemia, usually from embolic or thrombotic occlusion of isolated perforating paramedian arterioles or the basilar artery occlusion . Other etiologies include hemorrhage , tumor , inflammation and brain stem compression.
The oculomotor nerve enters the orbit as two separate divisions: the superior division, which innervates the levator palpebrae superioris and the superior rectus muscle, and the inferior division, which innervates the medial and inferior rectus muscles, the inferior oblique muscle, and the ciliary ganglion. An incomplete oculomotor nerve paresis in the distribution of either division is most often caused by a lesion in either the sphenocavernous region or the orbital apex. Orbital lesions that produce oculomotor nerve dysfunction usually produce other ocular motor dysfunction as well as visual loss and, in some cases, significant proptosis.

Now for our case,

Isolated medial rectus paralysis without involvement of other muscles supplied by the third nerve is very rare.

In the foreground of diagnostic features is a variable exotropia that decreases or may be completely absent when the affected eye is in abduction and increases exponentially as the paralyzed eye attempts adduction (secondary deviation).

A head turn toward the nonparetic side may allow the patient to attain single binocular vision.

Medial rectus paralysis must be distinguished from internuclear ophthalmoplegia (INO), caused by lesions in the medial longitudinal fasciculus. In this condition limitation of adduction is associated with nystagmus when the eye is abducted . Convergence may or may not be normal.

A clinical picture similar to INO or medial rectus paralysis may be simulated by myasthenia gravis. A Tensilon test may be indicated .

Surgery may be done on the affected eye or may be divided between the paralyzed and the sound eye and consists of resection of the paralyzed medial rectus and recession of its yoke muscle, the lateral rectus of the sound eye, or recession of the ipsilateral lateral rectus muscle. In the case of complete paralysis with exotropia in the primary position and with the head passively straightened, a full tendon transfer of the vertical recti to the insertion of the medial rectus muscle may be indicated.