Association Between Positive Occipital Sharp Transients of Sleep and Lambda Waves

Positive occipital sharp transients of sleep (POSTS) and lambda waves have similar morphology and location. We studied a possible association between these 2 normal EEG patterns. We reviewed a series of consecutive unselected ambulatory EEGs during a 3-month period (October 16, 2017 to January 19, 2018) and identified records with POSTS and records with lambda waves. Statistical analysis was performed using a chi-square test. A total of 140 ambulatory EEGs were reviewed. Duration of EEGs ranged from 24 to 168 hours (mean 76 hours). The population was 34% males, with ages ranging from 3 to 93 years (mean 48 years). Of the 140 records, 30 were abnormal, including 20 with epileptiform abnormalities. A chi-square test for independence (with Yates continuity correction) indicated a significant association between POSTS and lambda waves, χ²(1, n = 140) = 69.208, p < .001, φ = 0.72. In addition, 100% of records with lambda waves had POSTS, and 72% of records with POSTS had lambda waves. There is a high association between lambda waves and POSTS. This suggests a strong similarity between the 2 waveforms, and possibly a common occipital generator.