A 35-year-old right-handed man was admitted to the hospital because of a persistent headache and deviation of the tongue.The patient had been in excellent health until about one month earlier, when a left-sided headache developed, with occasional bright spots in the left visual field, subjective fever, chilliness, and anorexia; he lost 5 kg of body weight at this time. The headache became severe and was not affected by nonsteroidal antiinflammatory agents, the patient's position, straining, or coughing. During this period, his tongue deviated to the left and caused drooling, although he had no dysphasia or dysphagia.One week before admission, the patient was seen at a community health center affiliated with this hospital, where he reported a transient sore throat. Ibuprofen and amoxicillin were prescribed, but his condition did not improve. A throat culture was negative for beta-hemolytic streptococci. He was admitted to this hospital.The patient was a native of Morocco and had immigrated to the United States one year before admission. He worked as a cook. He had smoked one pack of cigarettes daily for 10 years and used marijuana occasionally; he did not drink alcohol. There was no history of arthralgia, vision loss, rash, motor or sensory deficits, neck stiffness, nausea, vomiting, chest or abdominal pain, cough, head injury or other trauma, exposure to tuberculosis, or other illnesses in recent months.The temperature was 37.1°C, the pulse was 53, and the respirations were 20. The blood pressure was 125/ 70 mm Hg.On physical examination, the patient appeared well. No rash or definite lymphadenopathy was found, although some examiners palpated left cervical fullness; the neck was supple. One senior examiner noted slight temporal-artery tenderness, without thickening.On neurologic examination, the patient was alert and oriented, with intact speech and comprehension. His cranial-nerve functions were also intact, except for questionable left-sided facial weakness, definite leftward deviation of the tongue, and questionably decreased elevation of the palate on the left side; the gag reflex was preserved. Motor power was 5/5 throughout, without drift, and sensation of a light touch and a pinprick was normal. Coordination was also normal. The deep-tendon reflexes were ++ throughout, and the plantar responses were flexor.The urine was normal. The hematocrit was 39.5 percent; the white-cell count was 12,000 per cubic millimeter, with 67 percent neutrophils, 25 percent lymphocytes, 5 percent monocytes, 2 percent eosinophils, and 1 percent basophils; the platelet count was 545,000 per cubic millimeter; the mean corpuscular volume was 86 µm 3 ; and the erythrocyte sedimentation rate was 99 mm per hour. The prothrombin and partial-thromboplastin times were normal. The uric acid level was 1.7 mg per deciliter (101 µmol per liter), and the total protein level was 7.9 g per deciliter (albumin, 3.5 g per deciliter; globulin, 4.4 g per deciliter). The sodium level was 142 mmol per liter, the potassium level 4.6 mmol per liter, th...