I read with interest the paper entitled, "The Efficacy of Botulism Neurotoxin A for the Treatment of Complete and Partially Recovered Chronic Sixth Nerve Palsy" (J Pediatr Ophthalmol Strabismus. 1994;31:79-83).
It has been my impression that unresolved cases of sixth nerve palsy with minimal abduction, no abduction, or negative abduction frequently show secondary contracture of the medial rectus as indicated by a preoperative positive forced duction that converts to negative when the medial rectus is disinserted.
With that in mind, if one examines the tables on page 81, one finds that in the successful group, 3 of 9 cases, or 33%, have marked limitation of abduction (cases 1, 2, and 7), while in the failure group, 8 of 13, or 62%, show marked limitation of abduction (cases 10, 11, 12, 14, 16, 17, 19, and 22). Because almost twice the number of patients with severe loss of abduction appear in the failure group compared with the success group, one might reasonably conclude that marked loss of abduction and possible secondary contracture were a significant factor in the outcome of treatment. Additionally, one might therefore choose to include medial rectus recession as part of the therapy in patients with no abduction or negative abduction with a positive forced duction test.
JOSEPH H. GOLDSTEIN, MD
Dr Goldstein accurately notes there is a trend toward greater treatment success with botulinum neurotoxin A for patients with chronic abducens nerve paresis with some abduction than for patients with marked limitation of abduction. The numbers of patients in our study, however, were too small to draw a scientifically valid conclusion regarding abduction and outcome. Dr Goldstein's suggestion that botulinum neurotoxin A be combined with a large medial rectus muscle recession is a reasonable extension of our findings. However, 3 of 11 patients with very poor abduction responded to injection alone. Thus, I believe a trial of chemodenervation before strabismus surgery is still worthwhile.
MICHAEL X. REPKA, MD