Functional Seizures and Chronic Pain: A Narrative Review of common Pathomechanisms and Clinical Implications

Background Functional seizures (FS) manifest as episodic events, bearing superficial similarities to epileptic seizures and represent a major component of Functional Neurological Disorder (FND). FS frequently present with the co-morbidity of chronic pain and the pronounced clinical and epidemiological associations between these conditions suggest potential shared pathomechanisms. Although conventional neuroimaging and neurophysiological assessments do not detect abnormalities in either condition, advanced biophysical signal analyses offer potential biomarkers. Method We undertook comprehensive literature review encompassing studies employing EEG, MEG, functional MRI, PET, and SPECT in FS and chronic pain. Due to the heterogenous nature of the collected data, the results of data extraction and analysis are presented in the form of a narrative synthesis. Results Despite some limitations, altered neural network dynamics are evident in both FS and chronic pain, revealing intriguing common mechanisms. Both conditions exhibit overactivation in sensorimotor networks and alterations in the Default Mode Network (DMN), impacting self-awareness and pain perception. Emotional processing regions, like the anterior cingulate cortex and insula, were affected in both conditions. Furthermore, Thalamocortical dysrhythmia(TCD) offers an intriguing link, influencing pain perception and seizure-like activities. Finally, suppressed alpha oscillations, linked to sensory perception, are prevalent in both conditions. Conclusion We identified shared neural mechanisms and a possible novel explanation (TCD) for co-occurrence of FS and chronic pain. These necessitate further exploration in subsequent studies incorporating patients exhibiting both disorders concurrently. Such research direction holds the potential to introduce novel therapies for not only managing FS or chronic pain, but also managing FND.