Duane Syndrome Workup

Updated: Mar 20, 2023
  • Author: Arun Verma, MD; Chief Editor: Hampton Roy, Sr, MD  more...
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Other Tests

On testing of brainstem auditory evoked responses, findings of Duane syndrome (DS) occasionally are abnormal, suggesting widespread neurologic abnormalities.

EMG findings show absent lateral rectus firing on attempted abduction and firing of both horizontal recti on attempted adduction.

The affected lateral rectus muscle behaves like a muscle double innervated by a weak abducens nerve and a stronger oculomotor nerve branch or like a muscle only innervated by an oculomotor nerve branch. This finding demonstrates that, though a muscle is present, it has a functioning yet abnormal nerve supply.

Likewise, simultaneous EMG recording of the lateral and medial recti muscles revealed a paradoxical innervation of the lateral rectus muscle to be the pathogenetic principle of all forms of Duane syndrome.


Histologic Findings

Early histopathologic and surgical studies led to the conclusion that Duane syndrome was a local, purely myogenic phenomenon. Therefore, the generally accepted concept was that the cause of abduction deficiency was fibrosis of the lateral rectus muscle and that the limitation of adduction was caused by a false posterior insertion of the medial rectus muscle or by adhesions between the medial rectus muscle and the orbital wall.

Miller and coauthors from the John Hopkins University performed complete intracranial and orbital pathologic examination of 2 cases of Duane syndrome in which the clinical findings were well documented. [20] The first case was bilateral Duane syndrome type 3. Postmortem examination of the brainstem and the posterior parts of the orbits revealed bilateral absence of the abducens nuclei and the abducens nerves. No large motor neurons were identified at levels the abducens nuclei normally occupy. No intra-axial fibers referable to the sixth cranial nerve could be identified with the brainstem. Both oculomotor nuclei and nerves were normal at the level of the ciliary ganglion; the inferior division of the oculomotor nerve divided into several branches penetrating the inferior medial aspect of the lateral rectus muscle.

The other case showed only 2 thin atrophic fibers of 0.1-mm diameter, both of which had separate exits (1 mm distance between them) from the dura. The further course of these fibers could not be examined.