Electromyography of extraocular muscles in Duane's syndrome.

The electromyographic (EMG) study of patients with Duane's retraction syndrome has shown that there is a gross abnormality of innervational pattern in this condition. Most commonly the lateral rectus is affected and shows an innervation differing from the normal in several respects. The first description of the EMG pattern in two patients came from Breinin (I957) when he reported little activity from one lateral rectus, which was found to be fibrotic and cordlike at operation. His other patient showed a low amplitude firing pattern with recruitment in adduction only. Papst and Esslen (I960), investigating five clinically typical cases, found increased innervation in the lateral rectus only in adduction. In five cases with minimal lid narrowing, co-contraction of the lateral and inferior rectus muscles was recorded in four cases and of the lateral and superior rectus muscles in one. Fourteen cases examined by Sato (i960) showed abnormal EMG responses from the lateral rectus muscles; six gave a paradoxical response (i.e. innervation decreasing in abduction and increasing in adduction), four gave an unvarying response with different gaze positions, and two showed a response which increased and decreased in the correct sense with abduction and adduction but to a lesser extent than normal. From the other two cases no response was obtained. Four cases reported by Orlowski and Wojtowicz (I962) showed that the lateral rectus muscles were innervated in the correct sense in horizontal gaze but with incomplete inhibition on adduction and poor recruitment in abduction compared with the normal response. These authors also found increased firing on downgaze from the lateral rectus in three cases and on upgaze in two cases, and postulated co-innervation between the superior, inferior, and lateral rectus muscles. Papst (I962) categorized different clinical varieties of Duane's syndrome and correlated them with abnormal co-contraction of: (i) Medial and lateral rectus; (2) Superior and lateral rectus; (3) Inferior and lateral rectus; (4) Lateral rectus and several other muscles. Burger (I963) found paradoxical innervation of the lateral rectus with low amplitude traces in two cases. This pattern remained unaltered when the medial rectus was rendered akinetic by local anaesthesia. Two further cases investigated by Orlowski and Krych (i963) showed paretic lateral rectus muscles with co-contraction between this and the inferior rectus (and to a lesser extent the superior rectus). Blodi, van Allen, and Yarbrough (i964), in two of six cases of Duane's syndrome, found abnormal firing of the