Botulinum toxin resistance may occur early in the course of treatment, usually within 2–3 years after starting treatment; the response usually fails gradually, starting with reduced duration of clinical effect, followed by significantly reduced maximal effect.

Patients with cervical dystonia should therefore be carefully monitored with scoring of the treatment effect in order to detect immunoresistance early, thereby avoiding complete therapy failure with high titres of neutralising antibodies.

Objective tests include unilateral injection of the frontalis muscle or injection of the extensor digitorum brevis of the foot with botulinum toxin. The frontalis test is the most frequently used method.

Any evidence of paralysis (frontalis or extensor digitorum brevis test) excludes immunoresistance as the cause of treatment failure.

Two injections of 30 units Dysport or 10 units of Botox or are given to the forehead about 3 cm above the lateral and medial canthus of one eye (figure 1).

The response is assessed 2–4 weeks later by asking the patient to raise their eyebrows: an asymmetric response indicates that botulinum toxin has been effective. To avoid equivocal results (especially in cases of partial resistance), it is valuable to compare photographs or videos before and after injection1.








1  Marion MH, Humberstone M, Grunewald R, Wimalaratna S. British neurotoxin network recommendations for managing cervical dystonia in patients with a poor response to botulinum toxin. Pract Neurol 2016; 16: 288–95.