Clinical Manifestations

Memory complaints are common in elderly and have various etiologies, including functional cognitive disorder (FCD). Diagnosis of FCD is supported by clinical evidence of incongruity with a neurodegenerative disorder and/or evidence of internal inconsistency - the ability to perform a task well at certain times, but with impaired ability at other times. The prevalence of features suggesting FCD in organic disorders is unclear. We assessed the presence of clinical features of internal inconsistency and other possible discriminators of FCD from organic causes in patients with mild cognitive impairment (MCI) and subjective cognitive impairment (SCI). Patients attending our tertiary memory clinic in a period of one year with SCI or MCI were included. Exclusion criteria were toxic or metabolic causes of cognitive decline, major psychiatric disorders, co-morbid neurological conditions that could affect cognition, and uncertainty of diagnosis of organic disorder or FCD. Medical records were reviewed for evidence of internal inconsistency and other suggested discriminators between functional and organic etiology. Demographic, cognitive and clinical data were compared between groups. We evaluated 39 patients with FCD and 57 with organic disorders. MCI was more common in patients with organic disorders. However, most patients with FCD also had MCI. Patients with FCD were younger and performed better on cognitive assessments, but with significant overlap between groups (Table 1). While patients with FCD more commonly attended the appointment alone and reported greater concern about their symptoms than their supporters, these features were unspecific (Table 2). Patients with FCD reported symptoms that could represent normal experiences and provided detailed descriptions of memory lapses more commonly. While less sensitive, memory perfectionism and symptoms occurring only in specific situations were highly specific for FCD. Differentiation between functional and organic cognitive disorders based on history and examination can be challenging. Features suggesting internal inconsistency and incongruity with neurodegeneration may also appear in organic causes of SCI and MCI. Their varying specificity and sensitivity for FCD need to be taken into account when considering the diagnosis. Improving the identification of FCD could in turn improve identification of patients with prodromal neurodegeneration.