A Critical Review of Alien Limb-Related Phenomena and Implications for Functional Magnetic Resonance Imaging Studies

Consensus criteria on corticobasal degeneration (CBD) include alien limb (AL) phenomena. However, the gist of the behavioral features of AL is still “a matter of debate.” CBD-related AL has so far included the description of involuntary movements, frontal release phenomena (frontal AL), or asomatognosia (posterior or “real” AL). In this context, the most frequent symptoms are language and praxis deficits and cortical sensory misperception. However, asomatognosia requires, by definition, intact perception and cognition. Thus, to make a proper diagnosis of AL in the context of CBD, cognitive and language dysfunctions must be carefully verified and objectively assessed. We reviewed the current literature on AL in CBD and now propose that the generic use of the term AL should be avoided. This catchall AL term should instead be deconstructed. We propose that the term AL is appropriate to describe clinical features associated with specific brain lesions. More discrete sets of regionally bound clinical signs that depend on dysfunctions of specific brain areas need to be assessed and presented when posing the diagnosis. Thus, in our opinion, the AL term should be employed in association with precise descriptions of the accompanying involuntary movements, sensory misperceptions, agnosia-asomatognosia contents, and the presence of utilization behavior. The review also offers an overview of functional magnetic resonance imaging-based studies evaluating AL-related phenomena. In addition, we provide a complementary set of video clips depicting CBD-related involuntary movements that should not mistakenly be interpreted as signs of AL.

From embodying tool to embodying alien limb: sensory-motor modulation of personal and extrapersonal space

Years ago, it was demonstrated (e.g., Rizzolatti et al. in Handbook of neuropsychology, Elsevier Science, Amsterdam, 2000) that the brain does not encode the space around us in a homogeneous way, but through neural circuits that map the space relative to the distance that objects of interest have from the body. In monkeys, relatively discrete neural systems, characterized by neurons with specific neurophysiological responses, seem to be dedicated either to represent the space that can be reached by the hand (near/peripersonal space) or to the distant space (far/extrapersonal space). It was also shown that the encoding of spaces has dynamic aspects because they can be remapped by the use of tools that trigger different actions (e.g., Iriki et al. 1998). In this latter case, the effect of the tool depends on the modulation of personal space, that is the space of our body. In this paper, I will review and discuss selected research, which demonstrated that also in humans: 1 spaces are encoded in a dynamic way; 2 encoding can be modulated by the use of tool that the system comes to consider as parts of the own body; 3 body representations are not fixed, but they are fragile and subject to change to the point that we can incorporate not only the tools necessary for action, but even limbs belonging to other people. What embodiment of tools and of alien limb tell us about body representations is then briefly discussed.

Corticobasal syndrome: a practical guide

Corticobasal syndrome is a disorder of movement, cognition and behaviour with several possible underlying pathologies, including corticobasal degeneration. It presents insidiously and is slowly progressive. Clinicians should consider the diagnosis in people presenting with any combination of extrapyramidal features (with poor response to levodopa), apraxia or other parietal signs, aphasia and alien-limb phenomena. Neuroimaging showing asymmetrical perirolandic cortical changes supports the diagnosis, while advanced neuroimaging may give insight into the underlying pathology. Identifying corticobasal syndrome carries some management implications (especially if protein-based treatments arise in the future) and prognostic significance. Its treatment is largely symptomatic and is best undertaken within a multidisciplinary setting, including a neurologist, physiotherapist, occupational therapist, speech language therapist, psychiatrist and, ultimately, a palliative care clinician. Corticobasal syndrome can be a confusing entity for neurologists, not least because it has over time evolved from being considered predominantly as a movement disorder to a condition spanning a wide range of cognitive and motor manifestations. In this practical review, we attempt to disentangle this syndrome and provide clarity around diagnosis, its underlying pathological substrates, key clinical features and potential treatments.

Three cases of paroxysmal alien limb phenomena due to epileptic seizures and review of literatures

Background The alien hand phenomenon (AHP) is a rare disorder of involuntary limb movement together with a loss of sense of limb ownership. AHP occurs as a consequence of frontal, callosal, or posterior cerebral lesions. To characterize the phenomenon of AHP, three patients with paroxysmal AHP were described and proved to be focal seizures by using video-EEG monitoring. Method Clinical history of 3 epileptic patients with AHP was collected. EEG and MRI were performed in each patient. One patient completed EEG monitoring and postoperative pathological examination. We also review the recent literatures and summarize the characteristics, types and hypothetic mechanisms of epileptic AHP. Results Case 1 had AHP of the left arm followed by the left arm convulsion or AHP only. MRI imaging showed a lesion in the posterior parietal lobe. After complete resection of the lesion, he remained seizure free for 1.5 years. Cases 2 and 3 had AHP and convulsion. The three cases did not have auto-motor signs, so they were identified to be the posterior type of APH. Conclusions The mechanism underlying AHP remains poorly .understood. Currently, little is known for the epileptic paroxysmal AHP, a quite rare form of AHP. AHP can be represented before or immediately after convulsion, or be represented by the paroxysmal symptom only.

Posterior Variant of Alien Limb Syndrome with Sudden Clinical Onset as Self-Hitting Associated with Thalamic Stroke

We present a case of sudden postischaemic onset of alien limb syndrome, with unintentional self-injury. Alien limb syndrome is an uncommon neurological disorder featured by uncontrolled and involuntary movements of a limb. Three variants of alien limb syndrome have been described: the anterior, featured by grasping of surrounding objects, the callosal, presenting with intermanual conflict, and the posterior, associated with involuntary levitation of the limb. Our patient suffered from an acute presentation of the posterior variant of the alien limb syndrome, resulting from an isolated thalamic stroke which was documented using 24-h computed tomography brain scan. Only one previous case of alien limb syndrome after thalamic infarct has been reported. Our case enhances the possibility that pure thalamic injury may represent a trigger for this condition.

Alien limb in the corticobasal syndrome: phenomenological characteristics and relationship to apraxia

Alien limb refers to movements that seem purposeful but are independent of patients’ reported intentions. Alien limb often co-occurs with apraxia in the corticobasal syndrome, and anatomical and phenomenological comparisons have led to the suggestion that alien limb and apraxia may be causally related as failures of goal-directed movements. Here, we characterised the nature of alien limb symptoms in patients with the corticobasal syndrome (n = 30) and their relationship to limb apraxia. Twenty-five patients with progressive supranuclear palsy Richardson syndrome served as a disease control group. Structured examinations of praxis, motor function, cognition and alien limb were undertaken in patients attending a regional specialist clinic. Twenty-eight patients with corticobasal syndrome (93%) demonstrated significant apraxia and this was often asymmetrical, with the left hand preferentially affected in 23/30 (77%) patients. Moreover, 25/30 (83%) patients reported one or more symptoms consistent with alien limb. The range of these phenomena was broad, including changes in the sense of ownership and control as well as unwanted movements. Regression analyses showed no significant association between the severity of limb apraxia and either the occurrence of an alien limb or the number of alien limb phenomena reported. Bayesian estimation showed a low probability for a positive association between alien limb and apraxia, suggesting that alien limb phenomena are not likely to be related to severity apraxia. Our results shed light on the phenomenology of these disabling and as yet untreatable clinical features, with relevance to theoretical models of voluntary action.

Alien limb in the corticobasal syndrome: phenomenological characteristics and relationship to apraxia

ABSTRACTAlien limb refers to movements that seem purposeful but are independent of patients’ reported intentions. Alien limb often co-occurs with apraxia in the corticobasal syndrome, and anatomical and phenomenological comparisons have led to the suggestion that alien limb and apraxia may be causally related as failures of goal-directed movements. Here, we characterised the nature of alien limb symptoms in patients with the corticobasal syndrome (n=30) and their relationship to limb apraxia. Twenty-five patients with progressive supranuclear palsy Richardson syndrome served as a disease-control group. Structured examinations of praxis, motor function, cognition and alien limb were undertaken in patients attending a regional specialist clinic. Twenty-eight patients with corticobasal syndrome (93%) demonstrated significant apraxia and this was often asymmetrical, with the left hand preferentially affected in 77% of patients. Moreover, 83% reported one or more symptoms consistent with alien limb. The range of these phenomena was broad, including changes in the sense of ownership and control as well as unwanted movements. Regression analyses showed no significant association between the severity of limb apraxia and both the occurrence of an alien limb and the number of alien limb phenomena reported. Bayesian estimation showed a low probability for a positive association between alien limb and apraxia, suggesting that alien limb phenomena are not likely to be related to severe apraxia. Our results shed light on the phenomenology of these disabling and as yet untreatable clinical features, with relevance to theoretical models of voluntary action.