Double elevator palsy (DEP) is a unilateral impairment of eye elevation. The name comes from the original belief that this condition is caused by a unilateral paresis of the superior rectus and inferior oblique muscles, the two muscles largely responsible for eye elevation. However, we now know that this is rarely the case, and that impairment of only one of the two elevator muscles is sufficient to produce this phenomenon. We also know that this condition has several possible causes that may be congenital or acquired in origin, and may be paretic or restrictive in nature.
Clinically, patients will present with an inability to elevate the affected eye. The inability to elevate occurs during both abduction and adduction, and the eye is often hypotropic in primary gaze. In some instances, the eyes are orthotropic in primary gaze. Patients will commonly present with associated pseudoptosis, ptosis, or a combination of these characteristics.
Pseudoptosis is the appearance of ptosis that is caused by hypotropia of the affected eye, and it is present in most cases. In contrast, true ptosis has also been observed in about 25% of cases of DEP, and it is attributed to paresis of the muscles that raise the eyelid. It is important to determine whether true ptosis is present, because it will usually require additional surgery after correction of DEP, whereas pseudoptosis will resolve.
DEP may also be associated with Marcus Gunn jaw-winking syndrome, a congenital condition that is characterized by ptosis and a rhythmic jerking of the upper eyelid that is triggered by jaw movement. This syndrome is thought to be caused by an aberrant connection between the motor branches of cranial nerve V3, which innervate the external pterygoid muscles, and the superior division of cranial nerve III, which innervates the levator palpebrae superioris muscle. Studies estimate that 25% of patients with DEP and congenital ptosis also have Marcus Gunn jaw-winking syndrome.
Three pathophysiologic mechanisms for DEP have been identified: primary inferior rectus restriction, primary superior rectus paresis or palsy, and congenital supranuclear elevation deficiency. These mechanisms may occur in isolation or in combination. Patients with long-standing superior rectus paresis often develop secondary contracture of the inferior rectus.
Diagnosis of DEP is primarily clinical. The presence of an intact Bell phenomenon—a protective ocular reflex where the eye deviates upward with eyelid closure—is suggestive of a supranuclear mechanism for DEP rather than a restrictive or paretic mechanism. Bell phenomenon is absent or impaired with restriction of the inferior rectus muscle or paresis of the superior rectus muscle.
The forced duction test (FDT) and forced generation test (FGT) are used to help distinguish between restriction and paresis. Patients with a primary inferior rectus restriction will have a positive FDT (ie, resistance to forced duction) with a normal FGT, whereas patients with a primary superior rectus paresis will have a normal FDT with reduced FGT. Both positive FDT and reduced FGT suggest combined restriction and paresis. Saccadic velocity testing can supplement the FDT and FGT in pinpointing the diagnosis.
Among these three mechanisms, inferior rectus restriction is most commonly observed to be associated with DEP. Scott and Jackson found that 73% of patients with DEP had restriction of the ipsilateral inferior rectus muscle. In addition to a positive FDT, they noted that many of these patients had an accentuated lower eyelid fold that became even more pronounced with attempted upward gaze.
In patients with a misalignment in primary gaze, correction of DEP is frequently necessary to prevent amblyopia or resolve an abnormal chin-up head position. Treatment for DEP is surgical, and the approach depends on the specific underlying mechanism that is identified.
In patients with inferior rectus restriction, an inferior rectus recession procedure is indicated. In patients with superior rectus paresis, the Knapp procedure is indicated; this consists of vertically transposing the medial and lateral rectus muscles to a point adjacent to the insertion of the superior rectus muscle.
Patients with both superior rectus paresis and inferior rectus restriction will require both procedures. Patients with DEP of supranuclear origin may require one or both of these procedures, depending on the degree of coexisting inferior restriction.
Any residual ptosis can be addressed after correction of the strabismus. The outcomes of these surgeries are generally positive; the most common complications are undercorrection or overcorrection.[2,8,12]
Medscape Ophthalmology © 2016
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