Stereotypic behaviours in frontotemporal dementia and progressive supranuclear palsy

Frontal lobe motor syndromes

The motor phenomena accompanying frontal lobe disease are diverse, reflecting the various roles the frontal lobes play in the organization of motor control. The principal frontal motor areas, the primary motor cortex, the premotor cortex, and the supplementary motor area, have different but interrelated functions in motor control. The principal efferent pathway of the primary motor cortex is the corticospinal tract which conducts fine motor control. Damage to the primary motor cortex and the corticospinal tract results in paralysis and loss of skilled, particularly distal, motor function. Lesions of the premotor cortex interfere with the preparation for the execution of movements and coordinating sequences of limb movement. Mediated through cortico-reticulospinal pathways, the premotor cortex adjusts axial and limb muscle activities. The fine motor skills of the corticospinal tract are superimposed upon these stabilizing movements. Supplementary motor area lesions interrupt self-initiated movements, release alien limb behaviors, and result in grasping. Paralysis, primitive reflexes, and frontal gait disorders are readily observed on examination, but difficulties initiating and sequencing movements are more subtle signs of perturbed higher motor control and require special examination procedures. Prefrontal motor syndromes include motor behaviors that only become apparent when the subject performs spontaneous or self-directed activities, unconstrained by instructions from the examiner. Clinical observation also reveals a slowness to respond to instruction with long delays before initiating action (inertia), but once underway they may be unable to stop (perseveration). Patients sit motionless without spontaneous movement or interest in their surrounds (apathy), yet exhibit distractibility, diverting attention to an incidental peripheral stimulus or an object with which they may then fiddle (environmental dependency and utilization behavior). Little spontaneous speech is initiated (abulia) but echolalia may be stimulated by the examiner's conversation. Restlessness, distractibility, perseveration, and environmentally dependent utilization behaviors coexist with apathy, inertia, and abulia. Mutism and akinesia may alternate with stereotypies and agitation in catatonia. These paradoxical combinations are of considerable diagnostic significance in recognizing frontal lobe motor syndromes.

Social Cognition in Behavioral Variant Frontotemporal Dementia and Pathological Subtypes: A Narrative Review

Behavioral variant frontotemporal dementia (bvFTD) belongs to the spectrum of frontotemporal lobar degeneration (FTLD) and is characterized by frontal dysfunction with executive deficits and prominent socioemotional impairments. Social cognition, such as emotion processing, theory of mind, and empathy may significantly impact daily behavior in bvFTD. Abnormal protein accumulation of tau or TDP-43 are the main causes of neurodegeneration and cognitive decline. Differential diagnosis is difficult due to the heterogeneous pathology in bvFTD and the high clinicopathological overlap with other FTLD syndromes, especially in late disease stages. Despite recent advances, social cognition in bvFTD has not yet received sufficient attention, nor has its association with underlying pathology. This narrative review evaluates social behavior and social cognition in bvFTD, by relating these symptoms to neural correlates and underlying molecular pathology or genetic subtypes. Negative and positive behavioral symptoms, such as apathy and disinhibition, share similar brain atrophy and reflect social cognition. More complex social cognitive impairments are probably caused by the interference of executive impairments due to increasing neurodegeneration. Evidence suggests that underlying TDP-43 is associated with neuropsychiatric and early social cognitive dysfunction, while patients with underlying tau pathology are marked by strong cognitive dysfunction with increasing social impairments in later stages. Despite many current research gaps and controversies, finding distinct social cognitive markers in association to underlying pathology in bvFTD is essential for validating biomarkers, for clinical trials of novel therapies, and for clinical practice.

Prevalence and determinants of motor stereotypies in autism spectrum disorder: A systematic review and meta-analysis

Stereotypies are frequently reported in people with autism spectrum disorder (ASD) but remain one of the less explained phenomena. We aimed to describe, through a systematic review and a meta-analysis, the prevalence of motor stereotypies in ASD and study the factors that influence this prevalence. Our literature search included MEDLINE, Scopus, and PsycINFO databases. Quality and risk of bias were assessed. Thirty-seven studies were included and the median prevalence of motor stereotypies in ASD was 51.8%, ranging from 21.9% to 97.5%. The most frequent determinants associated with a higher number of stereotypies in ASD were a younger age, lower intelligence quotient, and a greater severity of ASD. Moreover, gender did not seem to influence the prevalence of stereotypies. Meta-analytic analysis showed that lower IQ and autism diagnosis (independent of IQ) are associated with a higher prevalence of motor stereotypies (odds ratio = 2.5 and 4.7, respectively). Limitations of the reviewed literature include the use of convenience samples, with small sizes and heterogeneous inclusion criteria, and the predominance of high-functioning autism individuals.