[Neurophysiological methods in headache diagnosis].

Neurophysiological methods used in the diagnosis of headache, especially migraine are: electroencephalography (EEG), evoked cortical potentials (VEP, BAER, ERP), reflex responses, autonomic tests and transcranial magnetic stimulation (TMS). Interpretation of EEG can be important for the differential diagnosis of some disorders with headache as a presenting symptom. Noninvasiveness, accessibility and ability to repeat the test due to exposure to harmful ionization are the main advantages of EEG. The role of thorough medical history and clinical assessment in patients with headache should not be underestimated. Interictal EEG (between headache attacks) is not significant in routine evaluation of these patients, but can be useful in patients with unusual symptoms suggesting epilepsy or migraine. It is indicated in patients with an abrupt onset of headache, in patients with migraine followed by neurological signs, in basilar migraine, migraine with extended duration of aura and in cases where epilepsy is suspected. Headache as a symptom is present in various brain and systemic diseases and metabolic disorders. EEG changes seen in headache patients are not specific for a particular disorder, but can suggest additional evaluation and accelerate accurate diagnosis and earlier treatment. Visual evoked cortical potentials (VEP) and cognitive evoked potentials (ERP) in patients with migraine in interictal periods have shown differences in sensory processing between patients with headache and healthy controls. Neurophysiological methods (VEP, ERP) between migraine attacks show cortical hyperactivity and predisposition for further attacks. Brainstem auditory evoked responses (BAER) are a sensitive method for the detection of central nervous system damage. Activation of the brainstem during the migraine attack results in an amplitude increment seen soon after the end of the attack. According to recent studies, R2 component of the blink reflex was six times longer during migraine attack as compared to interictal values. This is thought to be a response to sensitization of the skin nociceptive afferent arch or other neurons in the trigeminal nucleus. In patients with cluster headache, autonomic tests generate cardiovascular and pupillary response suggesting systemic sympathetic hyperactivation connected to concurrent pupillary sympathetic hypofunction and modified opioid modulation. TMS is shown to be very useful for the detection of pathophysiological changes of numerous disorders including migraine, due to its excitatory and inhibitory effects. Recent studies have shown changes in motor and occipital cortex during TMS interictal excitability. Neurophysiological tests are used in differential diagnosis of headache, follow up of possible complications in patients with symptomatic headache as well as in neurorehabilitation. In addition, electrophysiological diagnostic test can contribute to better understand the headache pathophysiology.