Examination of Muscle Stiffness, Tenderness and Pressure Pain Thresholds During a Cycle of Botulinum Toxin A Treatment in Chronic Migraine Patients

or measuring the muscle stiffness, we use a linear 9 MHz ultrasound probe (9L) and the Logic E9 scanner, both from GE Healthcare (Chalfont St Giles, UK). All measurements are performed with the probe parallel to the muscle fibers. We will measure the stiffness of the trapezius muscle in the middle botulinum toxin A injection side (G1) according to the PREEMPT protocol. All data are saved as images by the observer and subsequently analyzed by a blinded observer.