Objective: To study WC and its response to EMG-Guided BTX

Background: Despite decades of use and popularity of BTX in WC, there is a paucity of studies reporting results of Rx, especially for EMG-guided injections, that potentially improve accuracy of muscle/fascicle targeting for toxin delivery to dystonic muscles. Whether patients choose to continue taking BTX depends on perceived improvement in hand function, counterbalanced by disadvantages of Rx (adverse effects, inconvenience and cost of repeated injections).

Method: 25 WC pts were recruited over 2y from a specialty BTX injection/MD Clinic. Careful clinical examination including mirror movements in affected hand (on writing with unaffected hand) were used to determine precise pattern of dystonic movements of thumb, digits 2-5, wrist, elbow,  and primarily dystonic muscles were chosen for injection. All injections performed under EMG-guidance using a MyoguideTM (Intronix, Canada) system by an experienced movement disorders specialist. Patients reassessed at 6 w and then till last follow-up (mean 14 mo). The primary outcome measure was the patient’s willingness to continue with Rx; secondary measures included impairment/disability scores on rating scales including WC rating scale, and measures of abnormal hand posturing, pain, writing ease and speed.

Results: 22 pts were male (mean age 24y, symptom duration 30 months) 14 pts were students who wrote for >3 hours/day.  Extensor and Flexor type WC patterns were seen in 13 and 7 subjects. Most commonly injected muscles: EPL,APL,EI,EDC 2,3 (extensor) and FPL,FDS/FDP2,3,FCRL,FCU (flexor group). Mean doses of BTX used:12.5u/muscle and 27.5u total (extensor group); 17.5u/muscle and 47.5u (flexor group). 23 pts chose to undergo repeat injections at 6 weeks, 2 chose to discontinue due to mild transient finger weakness. After 1 year, 18 patients were still under treatment and continued to benefit. All secondary outcome measures improved significantly in most patients and benefits were largely maintained at last follow-up.

Conclusion: The large majority of WC pts in this study were young male students. Extensor pattern affecting the thumb and index finger was the more common pattern of WC but a flexor pattern was also seen. EMG-guided BTX use was safe, well tolerated and effective in most subjects, with the large majority choosing to continue treatment despite its potential disadvantages.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-profile-and-response-to-emg-guided-botulinum-toxin-btx-injection-in-writers-cramp-wc-a-study-of-25-indian-patients/