Purpose: The purpose of the study was to evaluate the efficacy of botulinum toxin type A (BTX-A) injection in patients with acquired VI nerve palsy. Methods: Twenty-eight patients (16 F and 12 M), mean age 36.4 +/-- 17.8 DS;range 10 - 69 years with acquired VI nerve palsy, have been treated with BTX-A injection into the ipsilateral medial rectus, at least 6 months after onset. At 6 months follow up, a paresis and a paralysis, were respectively diagnosed if the affected eye could be actively abducted or not, across the mid-line;a simple horizontal rectus muscle procedure was performed for the paresis whilst for the paralysis, both a horizontal and vertical muscle transportation procedure were required. Results: A gradual physiological recovery of the lateral rectus muscle was observed in 9 (32%) patients (GROUP I) and surgical treatment was therefore unnecessary;the remaining 19 cases (68%), of which 5 paresis (GROUP II) and 14 paralysis (GROUP III) underwent surgery and within 1 year were all restored to orthotropia. Conclusion: Botulinum toxin type-A (BTX-A) injection is an invaluable tool in the differential diagnosis between paresis versus paralysis of the VIth nerve, allowing the correct choice of surgical procedure.
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