Abstract

FR.11.03

Trochlear nerve palsy: Differential diagnosis and therapy

Michael Gräf
Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Gießen und Marburg GmbH, Standort Gießen, Gießen

Trochlear nerve palsy is caused by peripheral neurogenic disturbance of the superior oblique muscle. Trochlear nerve palsy can be congenital or acquired. However, congenital palsy can only be presumed as a cause superior oblique weakness. The motility pattern corresponds to that of decompensated strabismus sursoadductorius, which can also be caused by hypoplasia of the superior oblique muscle, anomaly of its tendon’s path, lacking insertion of the tendon or any other connatal weakness of the superior oblique muscle. Causes of acquired trochlear nerve palsy are inflammation, trauma, compression, or ischemia of the nerve. In opposite to strabismus sursoadductorius, acquired trochlear nerve palsy requires neurologic diagnostic.
The ocular motility patterns of trochlear nerve and strabismus sursoadductorius mainly differ in the ratio of excyclo- and hyperdeviation of the affected eye. Strabismus sursoadductorius is characterized by large hyperdeviation which may be relatively comitant in up- and down-gaze and increases in adduction and decreases in abduction, while excyclodeviation is small. In trochlear nerve palsy hyperdeviation increases in down-gaze and the maximum excyclotropia nearly equals the vertical deviation (in degrees). The head-tilt phenomenon is positive in both conditions. BHilateral symmetric trochlear nerve palsy causes only slight or lacking vertical deviation, even in side-gaze and in the head-tilt test. Excyclotropia is large and increases in down-gaze. There is significant V-incomitance.
In case of strabismus sursoadductorius, surgical therapy can be performed without any delay, just depending on patient’s complaints. Surgery for acquired trochlear nerve palsy should be performed not earlier than 12 months after onset of palsy, if necessary after treatment of the causative disorder. Superior oblique tucking, inferior oblique recession, and the combination of both are possible. Augmentative surgery on the oblique muscles or recession of the contralateral inferior rectus muscle can be indicated as a second step.

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