Clinical Reasoning: A benign but potentially life-threatening headache

A previously healthy 51-year-old man presented with a 1-week history of severe daily bilateral temporal headaches, associated with neck pain and nausea, with no fever or thunderclap-like onset. His symptoms were orthostatic, occurring within several minutes of assuming the upright position, and alleviated within 5 minutes after lying down. He had no history of lumbar puncture or head or spinal trauma. Cranial CT and CT angiography in a local hospital had normal results. Bed rest and hydration for 4 days failed to relieve his symptoms. One day prior to admission at our hospital, he began to experience headaches even when he was lying flat. Upon admission, his neurologic examination was unremarkable except for neck stiffness.