Poewe 1998.

Methods	Randomised, double‐blind, parallel design Randomisation: not described Setting: multicentre (Germany and Austria) Duration: 8 weeks
Participants	75 participants enrolled (BtA 250 U group = 19; BtA 500 U group = 18; BtA 1000 U group = 18; placebo group = 20). % Female: all groups: 48% Mean age, SD: all groups: 47 years, 11.5 Mean CD duration, SD: all groups: 7.4 years, 6.7 CD severity (Tsui modified scale): BtA 250 U: 14.3; BtA 500 U: 13.1; BtA 1000 U: 14.5; placebo: 14.4 Inclusion criteria: Rotational CD with hyperactivity clinically confined to one splenius capitis muscle and the contralateral sternocleidomastoid muscle previously untreated with Bt Exclusion criteria: not mentioned
Interventions	BtA: Dysport (abobotulinumtoxinA); vials of 500 U, diluted with 1 mL sterile solution Placebo: 0.125 mg of human serum albumin and 2.5 mg of lactose, diluted with 1 mL sterile solution Study drug preparation: BtA provided in vials by Speywood Pharmaceuticals Muscles injected: a total of 2.5 mL of the study drug or placebo was injected in each participant (0.75 mL into 2 sites in the sternocleidomastoid muscle, and 1.75 mL into 2 sites in the splenius capitis muscle) EMG guidance: no BtA dose per participant: 250 U, 500 U, or 1000 U
Outcomes	Primary outcomes: Modified Tsui Scale score Secondary outcomes: Physician Global Assessment of Improvement (5‐point scale: worse, no improvement, improvement < 50%, improvement > 50%, remission) Patient Global Assessment of Improvement (5‐point scale: worse, no improvement, improvement < 50%, improvement > 50%, remission) Assessment of Swallowing Difficulties (5‐point scale: none, mild, moderate, severe, swallowing not possible) Adverse events Clinical Global Rating (taking into account efficacy and safety) Need for retreatment
Notes	Study discontinuations, reasons: BtA 250 U: n = 0 BtA 500 U: n = 2 (11%), lost to F/U: n = 2 BtA 1000 U: n = 0 Placebo: n = 0
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly assigned to receive treatment with placebo or total dose of 250, 500, or 1000 Dysport units of botulinum toxin type A in a double blind prospective study design" Comment: insufficient information about the sequence generation process to permit judgement of ‘low risk or high risk
Allocation concealment (selection bias)	Low risk	Comment: sequentially numbered drug containers of identical appearance
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Patients were randomly assigned to receive treatment with placebo or total dose of 250, 500, or 1000 Dysport units of botulinum toxin type A in a double blind prospective study design" Quote: "All three vials were identical in appearance"
Blinding of outcome assessment (detection bias) Objective outcomes	Unclear risk	Comment: insufficient information to permit judgement of low risk or high risk
Blinding of outcome assessment (detection bias) Subjective outcomes	Unclear risk	Comment: insufficient information to permit judgement of low risk or high risk
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "One patient in the 500 unit group was lost to follow up and had to be excluded from result analysis. A further case of 500 unit group had missed one follow up visit and was excluded from efficacy analysis but included in analysis of adverse events" Comment: reasons for missing outcome data unlikely to be related to true outcome
Selective reporting (reporting bias)	Low risk	Comment: the expected outcomes that are usually evaluated in intervention trials for this condition were reported in this study.
For‐profit bias	High risk	Quote: "Toxin and placebo preparations was supplied by Speywood Pharmaceuticals Ltd"
Enriched population – preferential enrolment of positive responders	Low risk	Comment: all participants were previously untreated with botulinum toxin type A
Enriched population – exclusion of poor responders	High risk	Quote: "Seventy five patients (...) with rotational torticollis and hyperactivity clinically confined to one splenius capitis and the contralateral sternomastoid muscles"