Pericranial Muscle Tenderness in a Population Based Sample of Chronic Tension-Type Headache. The Akershus Study of Chronic Headache

¹Head and Neck Research Centre, Akershus University Hospital, Lorenskog, Norway, Lørenskog, Norway; ²University of Oslo, Institute of Clinical Medicine, Nordbyhagen, Norway; ³Health Services Research, Research Centre, Akershus University Hospital, Lørenskog, Norway.