A 45-year-old man present with a daily headache over the past 3 weeks. Each attack lasts about an hour and awakens the patient from sleep. It is associated tearing and reddening of his right eye. The pain is deep, excruciating, and limited to the right side of the head. The neurologic examination is normal. The most likely diagnosis:

Cluster headaches, which can cause excruciating hemicranial pain, are notable for their occurrence during characteristic episodes. Usually attacks occur during a 4-to 8-week period in which the patient experiences one to three severe brief headaches daily. There may then be a prolonged pain-free interval before the next episode. Men between ages 20 and 50 are most commonly affected. The unilateral pain is usually associated with lacrimation, eye reddening, nasal stuffiness, ptosis, and nausea. During episodes alcohol may provoke the attacks. Even though the pain caused by brain tumors may awaken a patient from sleep, the typical history and normal neurologic examination do not mandate evaluation for a neoplasm of the central nervous system. Acute therapy for a cluster headache attack consists of oxygen inhalation, although intranasal lidocaine and subcutaneous sumatriptan may also be effective. Prophylactic therapy with prednisone, lithium, methysergide, ergotamine, or verapamil can be administered durinq an episode to prevent further cluster headache attacks.