Introduction:   Analysis of infra-slow EEG activity (ISA) may provide insight into the pathophysiology of infantile spasms (IS). ISA is thought to be generated in part by thalamo-cortical (TC) networks which also are recognized to underlie the expression of sleep spindles, both of which may be pathologically expressed in patients with IS. We investigated a potential correlation of ISA and sleep spindles in patients with IS. 

Methods:  In 13 cases of IS, EEG recordings were evaluated for spasms-associated ISA to determine whether ISA changes, were generalized (g), lateralized (l), mixed (m) or associated with no- ISA. Results were correlated with the occurrence and expression pattern of sleep spindles.

Results: A total of 101 spasms were analyzed and 88/101 (87.1%) were associated with ISA. G-ISA was observed in 4/13 (30.8%), l-ISA in 1/13 (7%), m-ISA in 6/13 (46.2%) and no-ISA in 2/13 (15.4%) patients. Sleep was captured in all patients and spindles were observed in (7/13) 53% of patients: g-ISA  2/4 (50%; 50% symmetric), m-ISA  3/6 (50%; all asymmetric), no-ISA 2/2 (100%; all symmetric). Sleep spindles were not observed in the patient with l-ISA. Notably 10/11 (91.0%) of patients with spasm-associated ISA had either asymmetric  or no recorded sleep spindles.

Conclusion: Spasm-associated ISA is likely pathologic, indicative of probable TC-dysfunction given the frequent co-occurrence of abnormal spindle expression and the normal spindle activity recorded in the two patients with no-ISA. Further research is needed to determine how TC dysfunction may lead to IS which may have both therapeutic and prognostic value.