Reduced left amygdala volume in patients with dissociative seizures (psychogenic nonepileptic seizures)

This study specifically investigated differences of amygdalar and hippocampal volumes between patients with dissociative seizures (DS), mesial temporal lobe sclerosis (MTS), and normal controls (NC).

Between 2003 and 2018, 127 patients diagnosed with DS and 278 with MTS were recruited. An additional 52 NC subjects were recruited between 2015 and 2018. We retrospectively selected 29 patients with DS (male:female, 6:23) with absence of structural confounding factors and obtained sex- and age-matched MTS and NC. We used Neuroreader to assess the volume of the amygdala and hippocampus as a percentage of total intracranial volume based on thin-slice (0.9-1.2 mm) T1-weighted images. Statistical analyses controlled for psychiatric comorbidity and logistic regression were used to evaluate efficacy of these values for individual-level diagnosis.

The left amygdala and right hippocampus were significantly smaller in DS compared to NC (both p = 0.04), which was not explained by differences in psychiatric comorbidity. When controlling for ipsilateral hippocampal or amygdala volume, which was seen equally in all groups (Spearman, p < 0.02), these differences were no longer significant (amygdala, p = 0.16, hippocampus, p = 0.18), suggesting that amygdalar and hippocampal atrophy may reflect network or regional changes rather than focal abnormalities. The three-way accuracy for differentiating DS, MTS, and NC using these data was 64 % (95 % confidence interval: 54-74 %).

Volumetric analysis demonstrates smaller left amygdalar and right hippocampal volumes in patients with DS compared to NC, which may mirror abnormalities in functional networks seen in conversion disorders and post-traumatic stress disorder.