Amyloid PET imaging in clinical practice

Amyloid positron emission tomography (PET) imaging enables in vivo detection of brain Aβ deposition, one of the neuropathological hallmarks of Alzheimer's disease. There is increasing evidence to support its clinical utility, with major studies showing that amyloid PET imaging improves diagnostic accuracy, increases diagnostic certainty and results in therapeutic changes. The Amyloid Imaging Taskforce has developed appropriate use criteria to guide clinicians by predefining certain scenarios where amyloid PET would be justified. This review provides a practical guide on how and when to use amyloid PET, based on the available research and our own experience. We discuss its three main appropriate indications and illustrate these with clinical cases. We stress the importance of a multidisciplinary approach when deciding who might benefit from amyloid PET imaging. Finally, we highlight some practical points and common pitfalls in its interpretation.

Dual-task interference and brain structural connectivity in people with Parkinson's disease who freeze

BACKGROUND

Freezing of gait in people with Parkinson's disease (PD) is likely related to attentional control (ie, ability to divide and switch attention). However, the neural pathophysiology of altered attentional control in individuals with PD who freeze is unknown. Structural connectivity of the pedunculopontine nucleus has been related to freezing and may play a role in altered attentional control; however, this relationship has not been investigated. We measured whether dual-task interference, defined as the reduction in gait performance during dual-task walking, is more pronounced in individuals with PD who freeze, and whether dual-task interference is associated with structural connectivity and/or executive function in this population.

METHODS

We measured stride length in 13 people with PD with and 12 without freezing of gait during normal and dual-task walking. We also assessed asymmetry of pedunculopontine nucleus structural connectivity via diffusion tensor imaging and performance on cognitive tests assessing inhibition and set-shifting, cognitive domains related to freezing.

RESULTS

Although stride length was not different across groups, change in stride length between normal and dual-task gait (ie, dual-task interference) was more pronounced in people with PD who freeze compared to non-freezers. Further, in people with PD who freeze, dual-task interference was correlated with asymmetry of pedunculopontine nucleus structural connectivity, Go-NoGo target accuracy (ability to release a response) and simple reaction time.

CONCLUSIONS

These results support the hypothesis that freezing is related to altered attentional control during gait, and suggest that differences in pedunculopontine nucleus connectivity contribute to poorer attentional control in people with PD who freeze.

Spatial neglect

The syndrome of visuospatial neglect is a common consequence of unilateral brain injury. It is most often associated with stroke and is more severe and persistent following right hemisphere damage, with reported frequencies in the acute stage of up to 80%. Neglect is primarily a disorder of attention whereby patients characteristically fail to orientate, to report or to respond to stimuli located on the contralesional side. Neglect is usually caused by large strokes in the middle cerebral artery territory and is heterogeneous, such that most patients do not manifest every feature of the syndrome. A number of treatments may improve neglect, but there is no widely accepted universal approach to therapy. Although most patients recover spontaneously, the evidence suggests that they continue to have significant cognitive impairments, particularly relating to attention.

Attention! A good bedside test for delirium?

BACKGROUND

Routine delirium screening could improve delirium detection, but it remains unclear as to which screening tool is most suitable. We tested the diagnostic accuracy of the following screening methods (either individually or in combination) in the detection of delirium: MOTYB (months of the year backwards); SSF (Spatial Span Forwards); evidence of subjective or objective 'confusion'.

METHODS

We performed a cross-sectional study of general hospital adult inpatients in a large tertiary referral hospital. Screening tests were performed by junior medical trainees. Subsequently, two independent formal delirium assessments were performed: first, the Confusion Assessment Method (CAM) followed by the Delirium Rating Scale-Revised 98 (DRS-R98). DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, fourth edition) criteria were used to assign delirium diagnosis. Sensitivity and specificity ratios with 95% CIs were calculated for each screening method.

RESULTS

265 patients were included. The most precise screening method overall was achieved by simultaneously performing MOTYB and assessing for subjective/objective confusion (sensitivity 93.8%, 95% CI 82.8 to 98.6; specificity 84.7%, 95% CI 79.2 to 89.2). In older patients, MOTYB alone was most accurate, whereas in younger patients, a simultaneous combination of SSF (cut-off 4) with either MOTYB or assessment of subjective/objective confusion was best. In every case, addition of the CAM as a second-line screening step to improve specificity resulted in considerable loss in sensitivity.

CONCLUSIONS

Our results suggest that simple attention tests may be useful in delirium screening. MOTYB used alone was the most accurate screening test in older people.

48, XXYY syndrome associated tremor

48, XXYY syndrome is a form of sex chromosome aneuploidy that affects between 1 in 18 000 to 1 in 40 000 males. It is not inherited and is diagnosed by karyotyping. It has similarities to 47, XXY Klinefelter's syndrome, with tall stature, micro-orchidism, hypergonadotropic hypogonadism and infertility in males. However, patients with 48, XXYY syndrome also commonly have dental problems, tremor, attention deficit disorder, learning difficulties, allergies and asthma. The tremor is typically reported as an intention tremor (in 71% of patients XXYY aged >20 years with 48), which becomes more common with age and worsens over time.

REACTION TIME AND SERIAL RESPONSE EFFICIENCY ON AROUSAL FROM SLEEP

Ss aroused from afternoon sleep show a significant decrement in discrimination reaction time task and a serial response task immediately on arousal.

AN EYE MOVEMENT PHENOMENON RELATING TO ATTENTION, THOUGHT AND ANXIETY

An eye movement phenomenon, which is thought to be related to the shifting of attention and personal ways of handling anxiety, is described and discussed in relation to certain research hypotheses.

EYE MOVEMENTS DURING VIGILANCE

This study concerns eye movements recorded during a vigilance situation. Evidence was obtained on where people looked when they were watching for signals, which were 0.5-sec. pauses in the motion of a slowly revolving pointer. The following results were obtained: (1) Detection probability for two dials was approximately half the detection rate for one dial. (2) Analysis of eye-movement records showed that in the one-dial situation every missed signal was fixated without being recognized. (3) In the two-dial condition, signals were not only either fixated or unfixated, but some were fixated for part of their duration. Approximately one-third of the signals fell into each fixation category. (4) In contrast to the one-dial condition, the largest proportion of unreported signals for two dials were not fixated at all. Nearly as many unreported signals were partially fixated. About one-quarter of the unreported signals were fixated for their full duration. (5) Individual Ss differed with respect to the time they paused on one dial before shifting to the other. Those who shifted more frequently detected more signals.

MODIFICATION OF OBSERVING BEHAVIOR

The effects on monitoring performance of a limited hold (LH) terminated by a bell or by electric shock and of periodic rest periods were investigated. The sensitivity of basal skin conductance to different monitoring conditions was also studied. Humans monitored a visual display in several 2-hr sessions under the Holland procedure. In each session, signals were programmed by one of the following three multiple schedules: a variable interval of 6 min (VI 6) and a VI 6 with a limited hold (LH) terminated by a bell; a VI 6 and a VI 6 LH terminated by electric shock; a VI 6 LH terminated by shock and a time-out (TO). The two components of each schedule alternated at 15-min intervals. The average observing response rate of eight subjects was lowest during the VI 6 periods, higher in periods when the LH was terminated by a bell, and highest when the LH was terminated by shock. Periodic TO periods did not appreciably increase the response rate under the VI 6 LH shock component. A differential level of palmar skin conductance under the two components of a schedule was present only under the mult VI 6 LH shock-TO.

A FACTOR-ANALYTIC STUDY OF DAYDREAMING AND CONCEPTUALLY-RELATED COGNITIVE AND PERSONALITY VARIABLES

This report summarizes a study of the factorial composition of a series of measures of the structure and content of daydreaming behavior. The relationships of fantasy to measures of divergent thought productivity, attention, curiosity, and personality measures are examined.

THE DISTRIBUTION OF OBSERVING RESPONSES IN A MIXED FI-FR SCHEDULE

In Exp I, three pigeons were trained on an observing response procedure where observing responses produced a stimulus correlated either with FI or with FR. Stimulus duration was 30 sec. During FR, the subjects completed the ratio before the stimulus terminated. During FI, the subjects usually observed the stimulus only once. Observing responses occurred immediately after food reinforcement. In Exp II, stimulus duration was shortened to 5 sec and the FR for food was increased. The results were similar to those of Exp 1. During most FIs and FRs, only one observing response occurred. The results of both experiments could be interpreted in a response competition framework. Immediately after food reinforcement, observing behavior is strong. When behavior on the food key begins it competes with further observing behavior.

THE EFFECT OF DISTRACTION ON SCHIZOPHRENIC PERFORMANCE. 2. PSYCHOMOTOR ABILITY

In the preceding paper the effect of experimental distraction was examined and the findings discussed. The present report is concerned with a similar study of the effect of distraction on tests which involve another aspect of schizophrenic performance, that of psychomotor ability. Earlier studies (Chapman and McGhie, 1961, 1962) produced both clinical and experimental evidence that auditory distraction disrupted the motor responses of some schizophrenic patients. As the previous experimental findings were based on two tests involving only very limited areas of psychomotor performance, it was necessary to examine patients on a wide range of psychomotor tests. A second aim of the present investigation was to assess any differential effects due to variation in the sensory modality of the distracting stimuli.

THE EFFECT OF DISTRACTION ON SCHIZOPHRENIC PERFORMANCE. 1. PERCEPTION AND IMMEDIATE MEMORY

In recent years an increasing number of workers investigating schizophrenic behaviour have concluded that many of the symptoms found in schizophrenia are related to a disturbance in the selective and inhibitory functions of attention. One of the earliest statements of this argument is found in Norman Cameron's (1938, 1939, 1944) concept of “over-inclusion”, which he used to describe the schizophrenic patient's tendency to include many elements irrelevant to the central idea in his thinking. Shakow (1962) reached the following conclusions in summarizing his own psychological studies of schizophrenia—“It is as if, in the scanning process which takes place before the response to stimulus is made, the schizophrenic is unable to select out the material relevant for optimal response. He apparently cannot free himself from the irrelevant among the numerous possibilities available for choice.” Weckowicz and Blewett (1959), in their studies of alterations in perceptual constancy in schizophrenic patients, interpreted their findings as suggesting that the patient's basic difficulty was that of “an inability to attend selectively or to select relevant information“. Venables and his colleagues (1959, 1962, 1963), in a series of studies on the arousal level of schizophrenic patients, also concluded that many of the behavioural abnormalities demonstrated were due to variations in the range of attention. In a series of investigations carried out by Payne and his colleagues (1960, 1961, 1963) to develop Cameron's concept of over-inclusive thinking in schizophrenia, the authors utilized Broad-bent's (1958) model of selective attention to postulate that this form of thought disorder is basically due “to a defect in some hypothetical central filter mechanism, the function of which

is to screen out irrelevant data both internal … and external … to allow for the most efficient processing of incoming information”.