The Impact of Comorbidities and Expectations on Functional Neurological Disorder Symptoms (FND)

Abstract

Functional Neurological Disorder (FND) is a condition that encompasses a wide spectrum of neurological symptoms that do not have an organic explanation. It is not clear why some patients develop a specific neurological symptom. In our study we considered the most frequent FND sub-types: functional motor disorders (FMD) and non-epileptic seizures (NES). It has been purported that individuals with risk factors, create strong expectations about body sensations based on clinical experiences such as disease, injury or surgery. These expectations would impact the nervous system which in turn lead to functional symptoms. These symptoms are inconsistent in frequency and evolution across time, and they are vulnerable to suggestion. Thus, there are no objective measures that can account for the symptoms. This thesis aims to determine whether previous clinical factors affecting different parts of the body have a relationship with the development of functional motor disorder (FMD) and non-epileptic seizures (NES), and to carry out a preliminary study of a measure capable of identifying perceptual differences in patients with functional weakness, the most reported symptom. In the first study we analysed the medical records of 108 FND patients (52 FMD and 56 NES), and in the second study we applied the Size-Weight Illusion (SWI) to 11 FND patients with functional weakness and 15 healthy controls (HC). It was found that patients with motor symptoms (FMD) had significantly higher rates of clinical factors that affected their limbs prior to the symptom onset than NES. Moreover, contrary to predicted, patients with NES had a similar rate of events that affected their head than FMD. However, NES had a higher rate of clinical factors during their lifetime than FMD, such as dissociative symptoms, suicidal ideation, and being victim of bullying, which affect the mind, and from the patients’ perspective they can be considered as located in the head. In the second study, FND and HC experienced a similar size-weight illusion. The severity and laterality of the symptom did not impact on the strength of the illusion, nor the dominance of the affected side. However, we propose that it is likely to find an effect in FND with a larger sample size. Otherwise, if similar results were found in future studies, the SWI might be a test that provides an objective assessment to confirm FND has a normal perception of weight relative to size.