Most routine laboratory and neuroimaging studies contribute to the diagnosis of spells primarily by helping to rule out other etiologies. EKG, cardiac Holter monitoring, CXR, or ventilation-perfusion lung scans may be diagnostic of cardiac-induced episodes. Serum glucose can point to fasting hypoglycemia, or an abnormal glucose tolerance test may reveal reactive hypoglycemia. Glucose tolerance testing would be done only for a high index of suspicion based on the clinical history. Spells thought to be related to alcohol or drug abuse can be investigated by toxic screens of blood or urine. An impression of vestibular disease can be investigated with quantitative calorics and nystagmography. No blood tests or special diagnostic studies are presently widely accepted for the diagnosis of complicated migraine, although provocative tests, such as the histamine challenge, have been advocated by some. In general, routine laboratory studies and neuroimaging should be performed selectively in diagnosis of spells, based on a suspicion for particular etiologies.
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