Addendum: Long-term Treatment Benefits and Prolonged Efficacy of OnabotulinumtoxinA in Patients Affected by Chronic Migraine and Medication Overuse Headache over 3 Years of Therapy - Guerzoni, Simona; Pellesi, Lanfranco; Baraldi, Carlo; Cainazzo, Michela Maria; Negro, Andrea; Martelletti, Paolo; Pini, Luigi Alberto (Frontiers in Neurology, 2018)