A 59 year old female with hypertension and stroke was evaluated for "visuals" and a "suspicious" ambulatory EEG. In her mid-20s headaches began around her menstrual period and continued until menopause. Headaches were presaged by a shimmering "heat wave" 15 minutes prior to a bilateral throbbing headache where she would seek a dark room and position of comfort to fight the pain and nausea until it abated. Gradually the headaches disappeared though she her "visuals" persisted without headache. She was seen by Neurology after experiencing an unwitnessed "black-out". A brain MRI revealed an old lacunar infarction in the left basal ganglia. An EEG was normal but an outpatient ambulatory EEG demonstrated "suspicious sharp waves". She was begun on topiramate but was unable to tolerate it. After seeking another opinion a follow-up EEG revealed the following:
Figure: EEG demonstrating rapid eye movement artifact and corresponding lambda waves (arrow). Note the time locked bilateral surface positive low-amplitude "sharp" waveforms. Recording parameters include longitudinal bipolar montage, sensitivity 7 uv, and filters of 1-70. Hz.
Lambda waves (LW)1 are surface positive occipital “sharp waves” rarely confused with epileptiform discharges. LW may be elicited on EEG if scanning eye movements of complex visual stimuli are encountered in a well-lighted environment. LW are usually < 50 uV, 200-300 msec duration, and recurrent in series time-locked to saccadic eye movements. LW are similar to POSTS in morphology, polarity, and location but are occur in wakefulness and as an evoked response while POSTS appear spontaneously and during physiologic sleep. An age relationship was suggested with LW greater in the 3-12 age range with prevalence that decreases over the lifecycle. LW are felt to be associated with occulomotor visual-integration. Our patient had migraine with aura and clinically suspected syncope. ASA accompanied by slightly higher doses of naldolol used for her hypertension yielded rare “visuals”. While TV may have triggered LW2 to appear on ambulatory EEG it was unable to be recovered to provide validation.
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