Botulinum toxin F in the treatment of torticollis clinically resistant to botulinum toxin A.

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Abstract
Two reports have shown a Japanese preparation of botulinum toxin type F (BTX-F) to be an effective alternative for patients with torticollis who develop clinical resistance to botulinum toxin type A (BTX-A). A group of patients with torticollis, comprising five secondary non-responders and one primary non-responder, were treated with a preparation of BTX-F produced in the UK (Speywood Pharmaceuticals). A low dose of BTX-F (220 mouse units (MU) in total) was given into clinically affected neck muscles, followed six weeks later by an injection of a total of 520 MU. Antibodies to BTX-A (mouse protection assay) were present in all secondary non-responders but not in the primary non-responder. No patients developed atrophy after injection of Dysport BTX-A (40 MU) into the left extensor digitorum brevis muscle whereas pronounced atrophy occurred in all patients after injection of 40 MU of BTX-F into the right extensor digitorum brevis muscle. Three patients improved subjectively after treatment with 220 MU BTX-F and five (all secondary non-responders) after the subsequent dose of 520 MU (two considerably), with reduced Tsui scores, but group scores were only significantly changed after the higher dose. The primary non-responder remained unchanged after both doses of BTX-F. One patient reported mild dysphagia with 520 MU BTX-F. Mean duration of improvement with 520 MU BTX-F was five (range 4-6)weeks. Thus BTX-F provides benefit for BTX-A non-responders with few side effects but for a shorter period than BTX-A, possibly due to relative underdosing. As with BTX-A, biological sensitivity to BTX-F does not necessarily predict a clinical response.