Progressive supranuclear palsy: loss of choline-acetyltransferase-like immunoreactive neurons in the pontine reticular formation

Deterioration of horizontal saccades in progressive supranuclear palsy

OBJECTIVE

To investigate horizontal saccade changes according to disease stage in patients with progressive supranuclear palsy (PSP).

METHODS

We studied visually and memory guided saccades (VGS and MGS) in 36 PSP patients at various disease stages, and compared results with those in 66 Parkinson's disease (PD) patients and 58 age-matched normal controls.

RESULTS

Both vertical and horizontal saccades were affected in PSP patients, usually manifesting as "slow saccades" but sometimes as a sequence of small amplitude saccades with relatively well preserved velocities. Disease progression caused saccade amplitude reduction in PSP but not PD patients. In contrast, VGS and MGS latencies were comparable between PSP and PD patients, as were the frequencies of saccades to cue, suggesting that voluntary initiation and inhibitory control of saccades are similar in both disorders. Hypermetria was rarely observed in PSP patients with cerebellar ataxia (PSPc patients).

CONCLUSIONS

The progressively reduced accuracy of horizontal saccades in PSP suggests a brainstem oculomotor pathology that includes the superior colliculus and/or paramedian pontine reticular formation. In contrast, the functioning of the oculomotor system above the brainstem was similar between PSP and PD patients.

SIGNIFICANCE

These findings may reflect a brainstem oculomotor pathology.

Head deviation in progressive supranuclear palsy: enhanced vestibulo-collic reflex or loss of resetting head movements?

It is unclear how the torticollis occasionally observed in patients with progressive supranuclear palsy (PSP) relates to vestibulo-collic reflex mechanisms. We report here the results of vestibular evoked myogenic potentials (VEMPs) in a PSP patient with forced head deviation in the opposite direction of turning, leading to torticollis for a few seconds. As VEMPs were normal bilaterally we conclude that an enhanced vestibulo-collic reflex per se is not the cause of the torticollis in our patient. The abnormal head deviation induced by turning in some PSP patients is best explained by damage to reticular nuclei responsible for resetting eye and head saccades. When such mechanisms are defective, unopposed vestibulo-collic reflexes can lead to eye and head deviations in the opposite direction of body turns.

Functional neuroanatomy of the human premotor oculomotor brainstem nuclei: insights from postmortem and advanced in vivo imaging studies

Considerable progress has been made recently in the field of the functional neuroanatomy of the primate oculomotor system, which has also improved our understanding of the structure, organization and function of the human oculomotor system. In the present review we provide for the first time an overview of the neuroanatomical basis of eye movement control in humans as revealed by a series of post-mortem studies in which the human premotor oculomotor brainstem nuclei were identified using unconventional 100 μm thick serial tissue sections stained for Nissl substance and lipofuscin pigment (Nissl-pigment stain according to Braak). Data from control brains and from patients suffering from spinocerebellar ataxia type 3, a neurodegenerative disease that severely impairs oculomotor function are discussed and recommendations for the identification of human premotor oculomotor brainstem nuclei in post-mortem studies are given. To visualize premotor brainstem nuclei in living patients, modern brain imaging techniques have been employed, albeit with limited success. Establishing topographic markers of brainstem nuclei may be a necessary next step to further elucidate the functional neuroanatomy of the premotor oculomotor brainstem network in human patients. This will help radiologists to identify these nuclei in living patients and will enable clinicians to monitor the progression of neurological disorders affecting the oculomotor system.

Progressive supranuclear palsy: clinical features, pathophysiology and management

Progressive supranuclear palsy (PSP) is a degenerative condition of unknown aetiology that produces an akinetic-rigid form of parkinsonism characterised by early falls and abnormalities of extraocular movements. Mean age of onset is approximately 63 years, and mean survival from symptom onset is 9 years. Men are much more frequently affected than women. The classic clinical finding is supranuclear ophthalmoplegia, which may not present until late in the illness, if at all. The clinical diagnosis of PSP can be difficult to make, as the sites of pathology are heterogeneous. Structural and functional neuroimaging studies, although not specific for PSP, may be of some assistance in making the diagnosis. The definitive diagnosis of PSP requires the presence of both clinical and neuropathological evidence. Multiple anatomical sites are affected in PSP. The most consistently involved are the subthalamic nucleus, globus pallidus interna and externa, pontine nuclei, periaqueductal grey matter and the substantia nigra. The location of the pathology accounts for the clinical features. The histological hallmark of PSP is the presence of globose neurofibrillary tangles in the affected subcortical nuclei. Neurofibrillary tangles are composed of abnormally phosphorylated tau, a microtubule-associated protein that is involved in maintenance of the cytoskeleton. Abnormalities near or in the gene coding for tau are implicated in the pathogenesis of PSP. The multiple neurotransmitter abnormalities, including those affecting dopamine, acetylcholine, gamma-aminobutyric acid and norepinephrine (noradrenaline) systems and pathways, as well as both pre- and post-synaptic pathology, make pharmacological therapy of PSP a challenge. Although an individual patient may respond to a drug, in general patients with PSP have a minimal response and a short duration of sustained benefit.

Early involvement of the tegmentopontine reticular nucleus during the evolution of Alzheimer's disease-related cytoskeletal pathology

The tegmentopontine reticular nucleus (nucleus of Bechterew) plays a crucial role in the generation of horizontal saccades and smooth pursuit movement of the eyes. The evolution of Alzheimer's disease-related cytoskeletal pathology was studied of this nucleus was studied in 27 autopsy cases at different stages of the cortical neurofibrillary pathology (NFT/NT stages I--VI). The first cytoskeletal changes were seen at stages I and II (preclinical Alzheimer's disease). At stages III and IV (incipient Alzheimer's disease), the nucleus exhibited a marked pathology, and it was severely involved at stages V and VI (clinically overt Alzheimer's disease). Damage to the tegmentopontine reticular nucleus most probably contributes to the hypometrie of horizontal saccades and the slowing of smooth pursuits that characteristically develop in patients suffering from Alzheimer's disease. Given the fact that pathological alterations of the tegmentopontine reticular nucleus begin early during the evolution of the underlying process, the question arises as to whether dysfunctional horizontal saccades and abnormal smooth pursuits could be employed as means of screening or diagnosing Alzheimer's patients in the very earliest stages of the disease.

Impairment of eyeblink classical conditioning in progressive supranuclear palsy

In a previous study we showed that learning in eyeblink classical conditioning (EBCC) is normal in Parkinson's disease (PD) and that the serial reaction time task (SRTT) is only marginally impaired. Since pathological lesions are more widespread in the atypical parkinsonian disorder of progressive supranuclear palsy (PSP) than in PD, we hypothesized that PSP patients may show more profound deficits in the EBCC and SRTT learning tasks. We therefore investigated EBCC with a delay and two trace paradigms, an SRTT and the California Verbal Learning Test (CVLT) in eight patients with PSP and an age-matched control group. In all EBCC paradigms, we found a significant difference between groups with no significant learning in PSP patients. In the SRTT, implicit learning may have been impaired, but verbal and manual sequence recall were only marginally impaired. Verbal memory was significantly worse in PSP patients than in the control group. Our study shows a dissociated pattern of learning abilities in PSP, where the EBCC as a measure of implicit learning is impaired, the explicit sequence detection in the SRTT is relatively preserved, and the verbal memory impaired. We hypothesize that the PSP patients' deficits in EBCC learning may be due to lesions of deep cerebellar nuclei. There may be a clinical role for EBCC in distinguishing PD and PSP patients.

The effect of transcranial magnetic stimulation on reaction time in progressive supranuclear palsy

OBJECTIVE

Reaction time is shortened when a startling acoustic stimulus (SAS) is delivered together with the 'go' signal in normal subjects and patients with Parkinson's disease (IPD), but not in patients with progressive supranuclear palsy (PSP). Similar shortening of reaction time has been reported in normal subjects and patients with IPD with transcranial magnetic stimulation (TMS). In this paper, we analyzed the effect of TMS on reaction time in patients with PSP.

METHODS

Six patients with PSP received the instruction to extend the wrist to a visual cue. In test trials, the visual signal was accompanied by either a SAS or a subthreshold TMS applied to the motor area. The same experimental paradigm was applied to 7 patients with IPD, and 10 normal subjects. We measured both reaction time and the slope of the initial accelerometric displacement (SAD).

RESULTS

Neither TMS nor SAS changed significantly reaction time in PSP patients. This observation was in contrast with the marked reaction time shortening induced by both stimuli in a similar amount in normal subjects and patients with IPD. Furthermore, SAS and TMS did not modify the SAD in PSP, but shortened it significantly in IPD.

CONCLUSION

The absence of an effect of TMS and SAS on reaction time in PSP patients suggests that these patients have a dysfunction in the mechanisms of facilitation of reaction time. The fact that TMS and SAS induced similar effects on reaction time in normal subjects, IPD and PSP patients indicate the possibility of common mechanisms of action for both types of stimuli.

Progressive supranuclear palsy

Progressive supranuclear palsy (PSP) or Steele-Richardson-Olszewski syndrome is a neurodegenerative disease of middle and late age. It is under-diagnosed not only by general physicians but also by neurologists. The cause of PSP is not known. Exposure to toxins and viruses has been proposed in the aetiology of PSP without any concrete evidence. The features of PSP resemble those of Parkinson's disease and the two diseases are often confused. Corticobasal degeneration and multisystem atrophy are other differential diagnoses. Despite certain common features with Parkinson's disease, corticobasal degeneration, and mutisystem atrophy, there are important differences that help to differentiate it from these disorders.

The ascending reticular activating system--from aminergic neurons to nitric oxide

The cholinergic neurons of the laterodorsal and pedunculopontine tegmental neurons are thought to comprise an important portion of the ascending reticular activating system. More recent work has demonstrated that the neurons of this cell group also released a number of neruoactive peptides and can produce nitric oxide in response to increases in intracellular calcium. The release of NO from the nerve terminals of these cells within the thalamus varies with behavioural state, being much lower during slow wave sleep than during wake and paradoxical sleep states. The NO release in the thalamus appears to act via the type II cGMP-dependent protein kinase present at high levels in the thalamic neurons. Thus the NO-cGMP signal transduction system can play an important role in regulating thalamic activity across behavioural states.

Brain muscarinic receptors in progressive supranuclear palsy and Parkinson's disease: a positron emission tomographic study

OBJECTIVES

To assess muscarinic acetylcholine receptors (mAChRs) in the brains of patients with progressive supranuclear palsy and Parkinson's disease, and to correlate the cholinergic system with cognitive function in progressive supranuclear palsy and Parkinson's disease.

METHODS

Positron emission tomography (PET) and [11C]N-methyl-4-piperidyl benzilate ([11C]NMPB) was used to measure mAChRs in the brain of seven patients with progressive supranuclear palsy, 12 patients with Parkinson's disease, and eight healthy controls. All of the patients with progressive supranuclear palsy were demented. The Parkinson's disease group consisted of 11 non-demented patients and one demented patient. The mini mental state examination (MMSE) was used to assess the severity of cognitive dysfunction in all of the subjects. The modified Wisconsin card sorting test (WCST) was used to evaluate frontal cognitive function in the non-demented patients with Parkinson's disease and controls.

RESULTS

The mean K3 value, an index of mAChR binding, was significantly higher for the frontal cortex in the patients with Parkinson's disease than in the controls (p<0.01). By contrast, the patients with progressive supranuclear palsy had no significant changes in the K3 values of any cerebral cortical regions. The mean score of the MMSE in the progressive supranuclear palsy group was significantly lower than that in the control group. Although there was no difference between the Parkinson's disease and control groups in the MMSE, the non-demented patients with Parkinson's disease showed significant frontal lobe dysfunction in the WCST.

CONCLUSIONS

The increased mAChR binding in the frontal cortex of the patients with Parkinson's disease may reflect denervation hypersensitivity caused by loss of the ascending cholinergic input to that region from the basal forebrain and may be related to frontal lobe dysfunction in Parkinson's disease. The cerebral cortical cholinergic system may not have a major role in cognitive dysfunction in progressive supranuclear palsy.

Supranuclear gaze palsy and eyelid apraxia in postencephalitic parkinsonism

We describe six patients with clinicopathologically confirmed post-encephalitic parkinsonism (PEP) in whom oculomotor abnormalities developed several years after suffering the initial episode of encephalitis lethargica. Four of the cases had vertical supranuclear gaze palsy and two eyelid apraxia, features typically associated with progressive supranuclear palsy (PSP). Our findings indicate that the presence of gaze palsy alone may not be a reliable clinical discriminator between PEP and PSP. Involvement of the dorsal central gray nucleus, nucleus centralis pontis oralis, nucleus dorsal raphe interpositus, rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), nucleus interstitialis of Cajal, nucleus of the posterior commissure, pedunculopontine nuclei and frontal cortex was observed in several of our PEP cases and may contribute to the oculomotor abnormalities in this disorder. Whether the dorsal tegmental nucleus, caudal to the supratrochlear nucleus, severely affected in all our PEP cases, has a role in vertical gaze needs to be further studied.

The acoustic startle response is normal in patients with multiple system atrophy

We investigated the acoustic startle response in eight patients with MSA and compared the results with those from a group of age matched healthy subjects. Onset latency and amplitude of the responses obtained in the orbicularis oculi, masseter and sternocleidomastoid muscles were not different in patients and control subjects. We conclude that, in spite of the pathological derangement described in brainstem reticular nuclei in MSA, the neuronal circuits mediating the auditory startle reflex are functionally preserved.

Loss of striatal high affinity NGF binding sites in progressive supranuclear palsy but not in Parkinson's disease

125I-Nerve growth factor (NGF) binding sites were analyzed by autoradiography in the striatum of 3 control subjects, 3 patients with Parkinson's disease and 3 patients with progressive supranuclear palsy. A high level of 125I-NGF binding was observed (0.3-0.4 fmol/mg of tissue equivalent) in the striatum and the nucleus basalis of Meynert of control patients. Pockets of lower 125I-NGF binding corresponding to acetylcholinesterase-poor striosomes were detected in the striatum of control subjects and patients with Parkinson's disease or progressive supranuclear palsy. When compared to controls, the density of 125I-NGF binding sites was reduced by 30% in the striatum of patients with progressive supranuclear palsy but not reduced in that of patients with Parkinson's disease. 125I-NGF binding was not significantly decreased in the nucleus basalis of Meynert in either diseases. Since NGF receptors are thought to be localized on cholinergic neurons in the striatum, the decrease in NGF binding is compatible with the loss of cholinergic neurons reported in the striatum from PSP patients.

Neurofibrillary tangles without cell loss in the lateral vestibular nucleus of patients with Alzheimer's disease

The lateral vestibular nucleus (LVN, nucleus of Deiters) was examined in the brains of four control subjects and four patients with dementia of the Alzheimer type (DAT). Neuronal counts on sections stained with silver and a polyclonal antibody to human choline acetyltransferase (ChAT) revealed an undiminished number of LVN neurons in patients with DAT. Numerous silver-stained neurofibrillary tangles (NFTs) were found in the DAT group, some also in the LVN of controls. These findings suggest that DAT affects LVN neurons, however without causing neuronal loss.

Pharmacological evaluation of the cholinergic system in progressive supranuclear palsy

Severe cholinergic loss occurs in the brains of patients with progressive supranuclear palsy. To evaluate the functional implications of this neuronal deficit, dose-response curves were obtained in patients with progressive supranuclear palsy and normal control subjects undergoing intravenous cholinergic blockade (scopolamine) and stimulation (physostigmine). Physostigmine had no significant neurobehavioral effects at any dose in patients with progressive supranuclear palsy. Scopolamine, at low and medium doses, significantly impaired memory performance of both groups, but worsened the gait of only the patients. High-dose scopolamine, which could not be tolerated by the patients, resulted in gait deterioration among control subjects. Thus, patients with progressive supranuclear palsy have increased sensitivity to cholinergic blockade compared to control subjects. Since loss of cholinergic neurons appears to contribute to the pathogenesis of certain cognitive and motor deficits found in progressive supranuclear palsy, the use of oral anticholinergics should ordinarily be avoided in this disorder. On the other hand, physostigmine at clinically tolerated dose levels seems to be therapeutically ineffective.

Eye movements in parkinsonian syndromes

Eye movements were recorded in 14 patients with Parkinson's disease (PD) in the "off" condition, 14 patients with striatonigral degeneration (SND), 10 patients with corticobasal degeneration (CBD), and 10 patients with progressive supranuclear palsy (PSP), with comparison with 12 control subjects. Vertical saccade paralysis was not observed in the PD, SND, and CBD groups but was present in 9 patients of 10 in the PSP group. In the PD and SND groups, horizontal reflexive visually guided saccade latency and accuracy were similar, and differed only slightly from those of controls. In the CBD group, saccade latency was significantly increased and correlated to an "apraxia score"; whereas, in the PSP group, saccade amplitude was significantly decreased. Thus, the abnormalities of both horizontal saccade parameters in the PSP group contrasted with those observed in the CBD group. The percentage of errors in the antisaccade task, an index of prefrontal dysfunction, was markedly increased only in the PSP group. The smooth pursuit gain was decreased in all groups but more severely in the PSP group. It may be concluded that saccade abnormalities are clearly different in SND, CBD, and PSP, and might help in early differential diagnosis in individual patients, but that SND cannot be differentiated from PD on the simple basis of eye movement abnormalities.

The auditory startle response in progressive supranuclear palsy

The EMG characteristics of the normal auditory startle response in man are compatible with an origin in the pontine reticular formation and with conduction down the spinal cord in a slowly conducting, possibly reticulo-spinal pathway. The startle was reduced or absent in patients with progressive supranuclear palsy, consistent with loss of neurones in the lower pontine reticular formation. In contrast, the startle was present and of normal form in patients with Parkinson's disease. However, it was delayed in onset. This result was not influenced by treatment with L-dopa. The late auditory startle in Parkinson's disease might be related to withdrawal of facilitatory input to brainstem centres from the basal ganglia.

The neuropathology of progressive supranuclear palsy

The macroscopical, histological, ultrastructural and immunocytochemical features of progressive supranuclear palsy (PSP) are reviewed. Recent investigations have revealed important differences in the distribution, ultrastructure and immunocytochemical profile of neurofibrillary tangles in PSP and in Alzheimer's disease. Cortical involvement, as demonstrated by the presence of tangles and neuropil threads has extended the neuropathological spectrum of PSP. Quantitative assessments of neuronal populations show neuronal loss, not only in various nuclei of the brainstem, diencephalon and cerebellum, but also in other areas, including the nucleus basalis of Meynert, substantia nigra and neostriatum. A new classification, based on neuropathological criteria, is suggested in order to take into consideration the phenotypic heterogeneity of PSP. This new classification distinguishes three types: typical, atypical and combined cases. Typical (Type 1) cases conform to the original definition of PSP. Type 2, atypical cases are variants of the histological changes characteristic of PSP: either the severity or the distribution of abnormalities, or both of these deviate from the typical pattern. Cases with combined pathology belong to type 3 group: in these the typical pathology of PSP is accompanied by lesions characteristic of another neurodegenerative or vascular disease.

Cholinergic approaches to the treatment of progressive supranuclear palsy

In spite of the severe loss of cholinergic neurons in the brains of patients with progressive supranuclear palsy (PSP), marginal or null benefits are seen in clinical trials after the administration of physostigmine, a cholinesterase inhibitor, or RS-86, a cholinergic agonist. The possible role of cholinergic therapy in PSP is reevaluated.

Cholinergic and peptidergic systems in PSP

PSP is associated with a widespread cholinergic deficit likely corresponding to a loss in cholinergic neurons. The cholinergic damage dramatically affects the basal ganglia and specific cell groups of the mesencephalon and pons. This provides an anatomically defined basis for motor and supranuclear oculomotor syndromes characteristic of PSP. Unlike Alzheimer's disease and Parkinson's disease with dementia, the disease is not associated with a marked cholinergic deficiency in the cerebral cortex. Various peptides are present at normal concentrations in extrapyramidal and limbic subcortical areas in brains of patients with PSP. Of particular interest, is somatostatin, the levels of which are subnormal in cerebral cortex of patients with dementia of Alzheimer' or Parkinson's disease type.

Therapy for progressive supranuclear palsy: past and future

Dysfunction of multiple brain systems in progressive supranuclear palsy (PSP) has complicated attempts to treat the disease. Neurotransmitter replacement strategies targeting the dopaminergic, cholinergic, and serotonergic systems have been unsuccessful. In order to bypass the degenerated cortico-striato-pallidal loop, we administered the adrenergic agonist idazoxan (IDA) to treat PSP in two randomized double-blind, placebo controlled, crossover studies. Approximately one half of patients enrolled in these studies showed statistically significant improvement in balance and manual dexterity while taking IDA compared to placebo. These results suggest that new therapies that target structures outside of the basal ganglia may be useful for symptomatic treatment of PSP. Applying this strategy and developing treatments that arrest or reverse clinical deterioration in PSP will require improved understanding of the process underlying the illness.