Table 2: Intervention, assessment and main results of selected studies.

First Author / Year Hand Muscles Affected Intervention/Type of Dose of BTX-A Type of Assessments/Outcome Measures Main Results
Tsui (1993) [10] FDS, FCR, FCU, FPL, EDC, ECU, PT,
BTX-A injection –
dose range 25–50 MU
1. Self-report assessment of participant writing on a four-point scale
2. Speed and accuracy of pen control
3. Gibson’s maze
4. Copying a standard passage (readability scoring by “blind” physician)
Self-reported results were modest: 4/20 had definite improvement, 2/20 had slight improvement.
8/12 participants described pain relief after BTX-A.
For speed, significant mean change in velocity from baseline to 2 weeks for BTX-A was recorded for horizontal movement (0.17 cm/sec, p < 0.05); for vertical movement (0.9 cm/sec, p < 0.01); and for descending movement (0.39 cm/sec, p < 0.05).
Mean time to complete Gibson’s maze significantly improved by 3.23 sec (p < 0.01) at 2 weeks, and by 3.63 sec (p < 0.01) at 6 weeks for participants on BTX-A.
Cole (1995) [11] FCR, APL, EPL, FDS, FPL, FCU, FDP, EDC BTX-A injection –
dose range 5–30 MU
1. Self-report response about improvement and weakness
2. Functional performance testing using:
a. MRC scales for muscle power
b. Timing of writing sample
c. Counting errors of writing “off-the-line” for WC
d. Counting the number of errors for a standard transcription for SC
e. MC participants played a standard piece of music which was recorded on videotape and assessed by five professors of music
4/10 participants had major improvement, 5/10 had moderate improvement and 1/10 had no improvement to BTX-A.
From MRC testing, 7/10 participants were weaker with BTX-A, 3/10 had no difference in strength after BTX-A, 2/10 had weakness after placebo.
4/6 participants with WC wrote faster after BTX-A.
2/2 participants with SC did not show any improvement in BTX-A compared to placebo.
2/2 participants with MC improved on BTX-A compared to placebo.
Kruisdijk (2007) [12] FPL, FDP, EIP BTX-A injection –
178 MU (range 30–240)
Placebo – volume equal to 224 MU (20–280)
1. Self-response to the question about benefit of treatment
2. Secondary outcome measures included:
a. Visual analogue scale (VAS) for handwriting
b. Symptom severity scale (SSS)
c. Functional status scale (FSS)
d. Writer’s cramp rating scale (WCRS)
e. Writing speed
Primary outcome – In the BTX-A group, 14/20 participants wished to continue treatment versus 6/19 participants in the placebo group.
Secondary outcome – The mean difference comparing placebo to BTX-A from baseline to 8 weeks of the objective measures were:
VAS: 1.32 cm (95% CI, 0.33 to 2.3, p = 0.01) in favor of BTX-A.
SSS: -2.44 points (95% CI, -4.52 to -0.37, p = 0.02) in favor of BTX-A.
FSS: 2.07 points (95% CI, -0.4 to 4.54, p = 0.1).
WCRS: -1.51 points (95% CI, -2.55 to -0.47,
p < 0.01) in favor of BTX-A.
Writing speed: 1.14 lines (95% CI, 0.07 to 2.20, p = 0.04) in favor of BTX-A.

FDS = Flexor Digitorum Superficialis; FCR = Flexor Carpi Radialis; FCU = Flexor Carpi Ulnaris; FPL = Flexor Pollicis Longus; EDC = Extensor Digitorum Communis; ECU = Extensor Carpi Ulnaris; PT = Pronator Teres; PQ= Pronator Quadratus; APL = Abductor Pollicis Longus; EPL = Extensor Pollicis Longus; FDP = Flexor Digitorum Profundus; EIP= Extensor Indicis Propius.
MU = Mouse Units; MRC = Medical Research Council