3. Study duration: 16 + 4 + 16 weeks. Eligible patients will be randomised at baseline to receive either Dysport® or Botox® and monitored at weeks 2, 4, 8, 12, 16 weeks. After 4 weeks of wash out period, then the patients get the other treatment (i.e, Patients who have got Dysport will be then administered with Botox)