New Study on Processing Speed in Patients with Functional Neurological Disorder
A recent study published the Journal of Neuropsychology concluded that patients with conversion disorder/functional neurological disorder (CD/FND) had clinically significant neurocognitive deficits compared to patients suffering from other somatic symptom disorders (SSRD), including significantly impaired information processing speed.
Conversion disorder (CD)/functional neurological disorder (FND) is defined in the DSM-5 by the presence of one or more deficits in voluntary motor or sensory functions, which causes significant suffering and a burden of disease in multiple areas of daily life. The disorder is common (Carson et al. 2000) and as equally physically debilitating as Parkinson’s disease, with greater impact on mental health and quality of life (Anderson et al. 2007; Voon et al. 2016). Still, it remains poorly understood. Symptoms are experienced as involuntary but have similar physiological features as voluntary movements (Hallett, 2010). An early crucial study hypothesized that a disturbance of volition might underlie FND (Spence et al. 2000). Patients may show symptoms of motor weakness, abnormal muscle contractions, loss of sensory functions, and/or non-epileptic seizures (Kozlowska et al., 2015; Krem, 2004).
While neurocognitive symptoms are common among individuals with other SSRD, little has been researched about the specific neurocognitive impairments in patients suffering from CD/FND (conversion disorder/ functional neurological disorder), such as non-epileptic seizures following trauma. The prevalence of CD/FND is approximately 0.7–5.0% (Uijen & Bischoff, 2011) and is more common among women than men (Feinstein, 2011; Krem, 2004; Uijen & Bischoff, 2011) with a typical onset between the ages of 10–35 (Uijen&Bischoff, 2011). Risk factors for CD/FND include psychological or physical trauma (Uijen& Bischoff, 2011).
The study examined neurocognitive functioning in patients with CD/FND and compared patients with other SSRD. The sample consistent of 318 patients; 29 were diagnosed with CD/FND with a mean age of 42.4, and 79.3% were women. The SSRD sample consisted of 289 patients with a mean age of 42.1, and 60.2% were women. All patients in the study completed a neuropsychological battery of tests that addressed a broad range of neurocognitive areas, including information processing speed, attention and executive function. Patients with CD/FND had clinically significant neurocognitive deficits in all neurocognitive domains based on the normative data comparison. They performed significantly worse than patients with other SSRD on information processing speed in particular.
Other recent studies have shown that CD/FND is associated with neurocognitive impairments in several domains, including attention (Brown, Nicholson, Aybek, Kanaan, & David, 2014; Demir, Celikel, Taycan, & Etikan, 2013; Kozlowska et al., 2015), learning (Demir et al., 2013), auditory–verbal memory (Brown et al., 2014), (working) memory (Brown et al., 2014; Demir et al., 2013; Kozlowska et al., 2015), executive functioning (Brown et al., 2014; Demir et al., 2013; Kozlowska et al., 2015), and visuospatial functioning (Demir et al., 2013).
This most recent study, as well as prior studies, shows that patients with CD/FND experience substantial neurocognitive impairments compared to population level, within the domains of information processing speed, attention, executive functioning, (working) memory, and language. The authors opined that depression and anxiety, or education, age, and gender, did not play an important role in the differences in neurocognitive functioning in patients with CD/FND versus those with other SSRD. When comparing the results of this study to the available literature, neurocognitive impairments in the domains of attention, working memory, verbal and visual memory, visuospatial functioning, and information processing speed are commonly found in patients with CD/FND (Brown et al., 2014; Demir et al., 2013; Kozlowska et al., 2015). This study also adds dysfunction in the language domain to the list of impairments, which are also found in the other SSRD group (Al-Adawi et al., 2010; Grace et al., 1999; Hall et al, 2011; Hart et al., 2000; Michiels & Cluydts, 2001; Moore et al., 2012; Niemi et al., 2002).
The findings of this study have implications for the treatment of CD/FND. In general, the effectiveness of cognitive behavioral therapy (CBT) remains equivocal (Conwill, Oakley, Evans, & Cavanna, 2014; Goldstein et al., 2010; Kuyk, Siffels, Bakvis, & Swinkels, 2008; LaFrance et al., 2014) for treating psychogenic non-epileptic seizures. A review of randomized controlled trials (Kroenke, 2007) reported only two randomized controlled trials which explored the effect of hypnosis in patients with CD but showed limited effects (Moene, Spinhoven, Hoogduin, & Van Dyck, 2002; Moene, Spinhoven, Hoogduin, & Van Dyck, 2003 ). Furthermore, neurocognitive dysfunction may lead to less efficient CBT, the treatment of choice in CD/FND. If CBT is negatively influenced by impaired cognitive functioning (i.e., patients forget the information that was taught during session or forget to do homework), CBT may not be the effective treatment that patients with CD/FND need. Cognitive remediation therapy (CRT) may be preferred in order to overcome neurocognitive problems, prior to offering CBT as a solution.
The authors concluded that future research on neurocognitive function in patients with CD/FND, compared to other patients with general SSRD, is needed. Future studies should also combine neurocognitive functioning in CD/FND with neurobiological correlates by using imaging, such as functional MRI.
 Journal of Neuropsychology (2021), 15, 69–87
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