Midbrain ataxia: an introduction to the mesencephalic locomotor region and the pedunculopontine nucleus

Concordant GRADE-3 Truncal Ataxia and Ocular Laterodeviation in Acute Medullary Stroke

Background: Severe truncal ataxia associated with an inability to sit up without assistance (STA grade 3) is frequent in patients with central acute vestibular syndrome (AVS) involving the brainstem or cerebellum. When these patients have nystagmus, central HINTS excludes peripheral lesions; however, additional localization and lateralization signs are helpful, not only to resolve the peripheral versus central vestibular lesion dilemma, but to zero in on a precise lesion localization/lateralization to the lateral medulla, the most common ischemic lesion localization associated with an initially false-negative stroke MRI. Methods: This is a study of AVS patients with additional inclusion criteria: grades 2 or 3 ataxia with an eventual diagnosis of medullary stroke (MS), either involving the lateral medulla (LMS) or the medial medulla (MMS), and horizontal (h) gaze paralysis was the main exclusion criteria. All patients sat on the side of the bed or stretcher, with assistance if needed. A general neurologic examination followed in the sitting position, the testing protocol included the head impulse, spontaneous nystagmus, and skew deviation (HINTS) tests, followed by observation of the effect of brief 3-5 sec eyelid closure on ocular position, and saccade and pursuit eye movement tests. If they could sit, the protocol included the ability to stand with a wide base, then a narrow base, the Romberg test, and tandem gait. Radiographic lesion localization and horizontal gaze deviation concluded the protocol. Results: A total of 34 patients met the entry criteria, 34 MS (13 in the lateral medulla, 12 previously described, and 1 new patient), and 1 new MMS. Among them, n = 10/12 had grade 3 ataxia, and 3 (1 new patient) had grade 2 ataxia. In addition, overt ocular laterodeviation (OLD) was present in thirteen of them (35.3%). All OLD patients had gaze deviation and ipsilateral saccade and truncal lateropulsion, 1 medial medulla stroke patient had grade 3 truncal contrapulsion and contralateral hemiparesis without OLD, n = 20/21 patients with LMS without OLD had grade 3 truncal ataxia, and 1 had grade 2 truncal ataxia. Discussion: AVS patients with severe truncal ataxia (inability to sit without assistance) potentially have brainstem, cerebellum, or subcortical lesions. All patients had central HINTS; however, simultaneous direction-concordant STA 3 and OLD provided greater lateral medulla localization specificity, affecting the ipsilateral medulla. Future work to explore a practical posterior circulation stroke scale that includes HINTS, STA, and OLD will potentially select cases for thrombolysis even in the event of initially false-negative imaging.

Nothnagel Syndrome

The internist Hermann Nothnagel (1841-1905) took a special interest in the cerebellum. In an early experimental study on rabbits conducted in 1876, he demonstrated the involvement of the vermis in the pathophysiology of motor ataxia. Between 1879 and 1889, he reported four cases of tectal tumors that clinically manifested with bilateral ophthalmoplegia and unilateral gait ataxia, culminating in the Cerebellar Classic highlighted here. Nothnagel attributed this clinical syndrome to lesions of the colliculi ("quadrigeminal bodies") and compression of the nuclei of the third cranial nerves, but also left open the possibility of the involvement of neighboring structures, such as the cerebellar vermis. Today, the ataxic component of Nothnagel syndrome is explained by a dorsal midbrain abnormality of either neoplastic or vascular origin, involving the superior cerebellar peduncles, besides the oculomotor nerves.

Demonstration of Microsurgical Technique and Nuances for the Resection of a Midbrain Tectal Glioma via the Transcollicular Approach: 3-Dimensional Operative Video

Tectal gliomas are a rare subset of intrinsic brainstem lesions. The microsurgical resection of these lesions remains a major challenge.1,2 Transcollicular approaches on one side, via the superior or inferior colliculi or both, are neurologically well tolerated without obvious or major auditory or oculomotor consequences. However, any postoperative acute visually triggered saccadic abnormalities caused by iatrogenic superior colliculus damage generally resolve during the postoperative period, as other oculomotor structures compensate for these functions in unilateral lesions.  In this surgical video, we present a 37-yr-old man with long-standing seizures, new onset headaches, progressive ataxic gait, and imbalance. Magnetic resonance imaging (MRI) showed a circumscribed nonenhancing dorsal midbrain cystic mass with compression on the aqueduct causing hydrocephalus. The lesion had a low signal intensity on T1-weighted images and a high signal intensity on T2-weighted images. The patient first underwent an endoscopic third ventriculostomy. Although his headaches greatly improved after the third ventriculostomy, he remained quite symptomatic in terms of gait imbalance and ataxia. The patient underwent a supracerebellar, infratentorial, transcollicular approach for resection of the tectal tumor. Simultaneously, motor and somatosensory evoked potentials were monitored.  Both the surgery and the postoperative course were uneventful, with postoperative MRI showing gross total resection of the mass, and histopathology indicating a WHO (World Health Organization) grade I pilocytic astrocytoma. The patient continued to do well without recurrence at 2-yr follow-up.  In this video, we demonstrate step-by-step microsurgical techniques for resecting these challenging tectal gliomas via the infratentorial-supracerebellar-transcollicular approach. The patient consented to the procedure and publication of his images.

Clinical Characteristics and Clinical Course of Body Lateropulsion in 47 Patients with Brainstem Infarctions

BACKGROUND

In patients with lower lateral medullary infarction (LMI) located under the vestibular nucleus, proprioceptive impairment due to dorsal spinocerebellar tract (DSCT) is considered a pathological condition for body lateropulsion. In patients with brainstem infarction located at or above the level of the vestibular nucleus, other pathways, such as the crossed vestibulothalamic tract (CVTT), are considered responsible.

RESEARCH QUESTION

The clinical course of body lateropulsion between each anatomical level of infarction remains unclear. Further, whether body lateropulsion refers to a static or a dynamic symptom also remains unclear.

METHODS

We examined 47 patients who exhibited body lateropulsion and categorized them into four groups: lower LMI under the vestibular nucleus, LMI at the level of the vestibular nucleus, pontine infarction, and midbrain infarction. The patients' time to acquire static upright standing position and gait in a straight line were statistically analyzed by a log-rank test using the Kaplan-Meier method.

RESULTS

Body lateropulsion in the static upright position was less frequent in the lower LMI group than in the other groups.

SIGNIFICANCE

Lower LMI primarily affected body lateropulsion in gait. DSCT damage could affect ipsilateral hip joint or leg coordination, causing body lateropulsion in dynamic situation.

Mental steps: Differential activation of internal pacemakers in motor imagery and in mental imitation of gait

Gait imagery and gait observation can boost the recovery of locomotion dysfunctions; yet, a neurologically justified rationale for their clinical application is lacking as much as a direct comparison of their neural correlates. Using functional magnetic resonance imaging, we measured the neural correlates of explicit motor imagery of gait during observation of in-motion videos shot in a park with a steady cam (Virtual Walking task). In a 2 × 2 factorial design, we assessed the modulatory effect of gait observation and of foot movement execution on the neural correlates of the Virtual Walking task: in half of the trials, the participants were asked to mentally imitate a human model shown while walking along the same route (mental imitation condition); moreover, for half of all the trials, the participants also performed rhythmic ankle dorsiflexion as a proxy for stepping movements. We found that, beyond the areas associated with the execution of lower limb movements (the paracentral lobule, the supplementary motor area, and the cerebellum), gait imagery also recruited dorsal premotor and posterior parietal areas known to contribute to the adaptation of walking patterns to environmental cues. When compared with mental imitation, motor imagery recruited a more extensive network, including a brainstem area compatible with the human mesencephalic locomotor region (MLR). Reduced activation of the MLR in mental imitation indicates that this more visually guided task poses less demand on subcortical structures crucial for internally generated gait patterns. This finding may explain why patients with subcortical degeneration benefit from rehabilitation protocols based on gait observation. Hum Brain Mapp 38:5195-5216, 2017. © 2017 Wiley Periodicals, Inc.

Pontomesencephalic Atrophy and Postural Instability in Wilson Disease

BACKGROUND AND PURPOSE

The MR Parkinsonism index helps in differentiating progressive supranuclear palsy from Parkinson disease and multisystem atrophy. Pontomesencephalic involvement is common in neurologic Wilson disease, but there is no prior study evaluating the MR Parkinsonism index and its indices in Wilson disease. We report the MR Parkinsonism index and its indices in Wilson disease and correlate these changes with clinical severity and postural reflex.

MATERIALS AND METHODS

Thirteen individuals with neurologic Wilson disease were included, and their clinical details, including neurologic severity, postural reflex abnormality, and location of signal changes on MR imaging, were noted. The 3D BRAVO T1 sequence was used for measurement of the MR Parkinsonism index and its indices. The MR Parkinsonism index and its indices were also obtained in 6 age- and sex-matched controls. The morphometric parameters in Wilson disease were compared with those in with healthy controls and among the patients with and without abnormal postural reflex.

RESULTS

The midbrain area was reduced in patients with Wilson disease compared with controls (112.08 ± 27.94 versus 171.95 ± 23.66 mm², P = .002). The patients with an abnormal postural reflex had an increased MR Parkinsonism index and pons-to-midbrain ratio compared with controls, whereas these parameters were equivalent in patients with normal postural reflex and controls. The patients with abnormal postural reflex had more severe illness, evidenced by higher Burke-Fahn-Marsden scores (51.0 ± 32.27 versus 13.75 ± 12.37, P = .04) and neurologic severity grades (2.57 ± 0.53 versus 1.67 ± 0.82, P = .04).

CONCLUSIONS

An increase in the MR Parkinsonism index in Wilson disease is mainly due to midbrain atrophy and it correlates with neurologic severity and abnormal postural reflex.

Paroxysmal freezing of gait in a patient with mesial frontal transient ischemic attacks

BACKGROUND

Rare patients have been reported who developed a mixture of gait disturbances following a focal lesion in the frontal lobe. Thus, the exact location of frontal lesion responsible for a specific gait disturbance is not well defined.

CASE PRESENTATION

We describe a 47-year-old man who experienced two episodes of paroxysmal freezing of gait of the right leg. During the attacks, he had no motor weakness, sensory change, or disequilibrium. He had past history of panic attacks. Recently, he had been under severe emotional stress. T2 and diffusion brain magnetic resonance imaging scans were normal. So far, the most likely clinical diagnosis might be functional freezing of gait. However, magnetic resonance angiography showed atherosclerosis in the proximal left anterior cerebral artery. Perfusion scans showed a delayed mean transit time in the left mesial frontal lobe. He developed two more attacks during the four months of follow up.

CONCLUSIONS

The presented case illustrates that the mesial frontal lobe may be important in the pathophysiology of freezing of gait. We speculate that the supplementary motor area may generate a neuronal command for the initiation of locomotion that in our case may have been inhibited by a transient ischemia.

Origins and Functions of the Ventrolateral VMH: A Complex Neuronal Cluster Orchestrating Sex Differences in Metabolism and Behavior

The neuroendocrine brain or hypothalamus has emerged as one of the most highly sexually dimorphic brain regions in mammals, and specifically in rodents. It is not surprising that hypothalamic nuclei play a pivotal role in controlling sex-dependent physiology. This brain region functions as a chief executive officer or master regulator of homeostatic physiological systems to integrate both external and internal signals. In this review, we describe sex differences in energy homeostasis that arise in one area of the hypothalamus, the ventrolateral subregion of the ventromedial hypothalamus (VMHvl) with a focus on how male and female neurons function in metabolic and behavioral aspects. Because other chapters within this book provide details on signaling pathways in the VMH that contribute to sex differences in metabolism, our discussion will be limited to how the sexually dimorphic VMHvl develops and what key regulators are thought to control the many functional and physiological endpoints attributed to this region. In the last decade, several exciting new studies using state-of-the-art genetic and molecular tools are beginning to provide some understanding as to how specific neurons contribute to the coordinated physiological responses needed by male and females. New technology that combines intersectional spatial and genetic approaches is now allowing further refinement in how we describe, probe, and manipulate critical male and female neurocircuits involved in metabolism.

Lesions causing freezing of gait localize to a cerebellar functional network

OBJECTIVE

Freezing of gait is a disabling symptom in Parkinson disease and related disorders, but the brain regions involved in symptom generation remain unclear. Here we analyze brain lesions causing acute onset freezing of gait to identify regions causally involved in symptom generation.

METHODS

Fourteen cases of lesion-induced freezing of gait were identified from the literature, and lesions were mapped to a common brain atlas. Because lesion-induced symptoms can come from sites connected to the lesion location, not just the lesion location itself, we also identified brain regions functionally connected to each lesion location. This technique, termed lesion network mapping, has been recently shown to identify regions involved in symptom generation across a variety of lesion-induced disorders.

RESULTS

Lesion location was heterogeneous, and no single region could be considered necessary for symptom generation. However, > 90% (13 of 14) of lesions were functionally connected to a focal area in the dorsal medial cerebellum. This cerebellar area overlapped previously recognized regions that are activated by locomotor tasks, termed the cerebellar locomotor region. Connectivity to this region was specific to lesions causing freezing of gait compared to lesions causing other movement disorders (hemichorea or asterixis).

INTERPRETATION

Lesions causing freezing of gait are located within a common functional network characterized by connectivity to the cerebellar locomotor region. These results based on causal brain lesions complement prior neuroimaging studies in Parkinson disease patients, advancing our understanding of the brain regions involved in freezing of gait. ANN NEUROL 2017;81:129-141.

Brainstem control of locomotion and muscle tone with special reference to the role of the mesopontine tegmentum and medullary reticulospinal systems

The lateral part of the mesopontine tegmentum contains functionally important structures involved in the control of posture and gait. Specifically, the mesencephalic locomotor region, which may consist of the cuneiform nucleus and pedunculopontine tegmental nucleus (PPN), occupies the interest with respect to the pathophysiology of posture-gait disorders. The purpose of this article is to review the mechanisms involved in the control of postural muscle tone and locomotion by the mesopontine tegmentum and the pontomedullary reticulospinal system. To make interpretation and discussion more robust, the above issue is considered largely based on our findings in the experiments using decerebrate cat preparations in addition to the results in animal experimentations and clinical investigations in other laboratories. Our investigations revealed the presence of functional topographical organizations with respect to the regulation of postural muscle tone and locomotion in both the mesopontine tegmentum and the pontomedullary reticulospinal system. These organizations were modified by neurotransmitter systems, particularly the cholinergic PPN projection to the pontine reticular formation. Because efferents from the forebrain structures as well as the cerebellum converge to the mesencephalic and pontomedullary reticular formation, changes in these organizations may be involved in the appropriate regulation of posture-gait synergy depending on the behavioral context. On the other hand, abnormal signals from the higher motor centers may produce dysfunction of the mesencephalic-reticulospinal system. Here we highlight the significance of elucidating the mechanisms of the mesencephalic-reticulospinal control of posture and locomotion so that thorough understanding of the pathophysiological mechanisms of posture-gait disorders can be made.

An estrogen-responsive module in the ventromedial hypothalamus selectively drives sex-specific activity in females

Estrogen-receptor alpha (ERα) neurons in the ventrolateral region of the ventromedial hypothalamus (VMHVL) control an array of sex-specific responses to maximize reproductive success. In females, these VMHVL neurons are believed to coordinate metabolism and reproduction. However, it remains unknown whether specific neuronal populations control distinct components of this physiological repertoire. Here, we identify a subset of ERα VMHVL neurons that promotes hormone-dependent female locomotion. Activating Nkx2-1-expressing VMHVL neurons via pharmacogenetics elicits a female-specific burst of spontaneous movement, which requires ERα and Tac1 signaling. Disrupting the development of Nkx2-1(+) VMHVL neurons results in female-specific obesity, inactivity, and loss of VMHVL neurons coexpressing ERα and Tac1. Unexpectedly, two responses controlled by ERα(+) neurons, fertility and brown adipose tissue thermogenesis, are unaffected. We conclude that a dedicated subset of VMHVL neurons marked by ERα, NKX2-1, and Tac1 regulates estrogen-dependent fluctuations in physical activity and constitutes one of several neuroendocrine modules that drive sex-specific responses.

MRI correlates of Parkinson's disease progression: a voxel based morphometry study

We investigated structural brain differences between a group of early-mild PD patients at different phases of the disease and healthy subjects using voxel-based morphometry (VBM). 20 mild PD patients compared to 15 healthy at baseline and after 2 years of follow-up. VBM is a fully automated technique, which allows the identification of regional differences in the gray matter enabling an objective analysis of the whole brain between groups of subjects. With respect to controls, PD patients exhibited decreased GM volumes in right putamen and right parietal cortex. After 2 years of disease, the same patients confirmed GM loss in the putamen and parietal cortex; a significant difference was also observed in the area of pedunculopontine nucleus (PPN) and in the mesencephalic locomotor region (MLR). PD is associated with brain morphological changes in cortical and subcortical structures. The first regions to be affected in PD seem to be the parietal cortex and the putamen. A third structure that undergoes atrophy is the part of the inferior-posterior midbrain, attributable to the PPN and MLR. Our findings provide new insight into the brain involvement in PD and could contribute to a better understanding of the sequence of events occurring in these patients.

Freezing of gait: moving forward on a mysterious clinical phenomenon

Freezing of gait (FoG) is a unique and disabling clinical phenomenon characterised by brief episodes of inability to step or by extremely short steps that typically occur on initiating gait or on turning while walking. Patients with FoG, which is a feature of parkinsonian syndromes, show variability in gait metrics between FoG episodes and a substantial reduction in step length with frequent trembling of the legs during FoG episodes. Physiological, functional imaging, and clinical-pathological studies point to disturbances in frontal cortical regions, the basal ganglia, and the midbrain locomotor region as the probable origins of FoG. Medications, deep brain stimulation, and rehabilitation techniques can alleviate symptoms of FoG in some patients, but these treatments lack efficacy in patients with advanced FoG. A better understanding of the phenomenon is needed to aid the development of effective therapeutic strategies.

REM sleep behavior disorder is not linked to postural instability and gait dysfunction in Parkinson

To evaluate a potential association of REM-sleep behavior disorder (RBD) with gait and postural impairment in Parkinson's disease (PD). Gait difficulties and postural impairment are frequent in PD and are a major cause of disability. Animal studies indicate a key role of the pedunculopontine nucleus (PPN) in gait, postural control, and REM sleep, and also in the pathophysiology of RBD. In humans, such an association has not been investigated. Twenty-six patients with mild-to-moderate PD (13 with polysomnography confirmed and 13 with excluded RBD), and 20 age-matched healthy controls were prospectively investigated. Gait assessment on a treadmill, and static and dynamic posturography were performed. PD patients with RBD do not differ from those without RBD in gait and postural control. Greater severity of PD or prevalence of gait and postural disturbances in the presence of RBD were not found. RBD was not associated with any particular motor phenotype. We found no association of RBD with gait disturbances and postural impairment. Human gait and postural control and RBD appear to depend upon different neuronal circuits.

The pedunculopontine nucleus area: critical evaluation of interspecies differences relevant for its use as a target for deep brain stimulation

Recently, the pedunculopontine nucleus has been highlighted as a target for deep brain stimulation for the treatment of freezing of postural instability and gait disorders in Parkinson's disease and progressive supranuclear palsy. There is great controversy, however, as to the exact location of the optimal site for stimulation. In this review, we give an overview of anatomy and connectivity of the pedunculopontine nucleus area in rats, cats, non-human primates and humans. Additionally, we report on the behavioural changes after chemical or electrical manipulation of the pedunculopontine nucleus. We discuss the relation to adjacent regions of the pedunculopontine nucleus, such as the cuneiform nucleus and the subcuneiform nucleus, which together with the pedunculopontine nucleus are the main areas of the mesencephalic locomotor region and play a major role in the initiation of gait. This information is discussed with respect to the experimental designs used for research purposes directed to a better understanding of the circuitry pathway of the pedunculopontine nucleus in association with basal ganglia pathology, and with respect to deep brain stimulation of the pedunculopontine nucleus area in humans.

Gait-related cerebral alterations in patients with Parkinson's disease with freezing of gait

Freezing of gait is a common, debilitating feature of Parkinson's disease. We have studied gait planning in patients with freezing of gait, using motor imagery of walking in combination with functional magnetic resonance imaging. This approach exploits the large neural overlap that exists between planning and imagining a movement. In addition, it avoids confounds introduced by brain responses to altered motor performance and somatosensory feedback during actual freezing episodes. We included 24 patients with Parkinson's disease: 12 patients with freezing of gait, 12 matched patients without freezing of gait and 21 matched healthy controls. Subjects performed two previously validated tasks--motor imagery of gait and a visual imagery control task. During functional magnetic resonance imaging scanning, we quantified imagery performance by measuring the time required to imagine walking on paths of different widths and lengths. In addition, we used voxel-based morphometry to test whether between-group differences in imagery-related activity were related to structural differences. Imagery times indicated that patients with freezing of gait, patients without freezing of gait and controls engaged in motor imagery of gait, with matched task performance. During motor imagery of gait, patients with freezing of gait showed more activity than patients without freezing of gait in the mesencephalic locomotor region. Patients with freezing of gait also tended to have decreased responses in mesial frontal and posterior parietal regions. Furthermore, patients with freezing of gait had grey matter atrophy in a small portion of the mesencephalic locomotor region. The gait-related hyperactivity of the mesencephalic locomotor region correlated with clinical parameters (freezing of gait severity and disease duration), but not with the degree of atrophy. These results indicate that patients with Parkinson's disease with freezing of gait have structural and functional alterations in the mesencephalic locomotor region. We suggest that freezing of gait might emerge when altered cortical control of gait is combined with a limited ability of the mesencephalic locomotor region to react to that alteration. These limitations might become particularly evident during challenging events that require precise regulation of step length and gait timing, such as turning or initiating walking, which are known triggers for freezing of gait.

Paraventricular hypothalamic nucleus: axonal projections to the brainstem

The paraventricular hypothalamic nucleus (PVH) contains many neurons that innervate the brainstem, but information regarding their target sites remains incomplete. Here we labeled neurons in the rat PVH with an anterograde axonal tracer, Phaseolus vulgaris leucoagglutinin (PHAL), and studied their descending projections in reference to specific neuronal subpopulations throughout the brainstem. While many of their target sites were identified previously, numerous new observations were made. Major findings include: 1) In the midbrain, the PVH projects lightly to the ventral tegmental area, Edinger-Westphal nucleus, ventrolateral periaqueductal gray matter, reticular formation, pedunculopontine tegmental nucleus, and dorsal raphe nucleus. 2) In the dorsal pons, the PVH projects heavily to the pre-locus coeruleus, yet very little to the catecholamine neurons in the locus coeruleus, and selectively targets the viscerosensory subregions of the parabrachial nucleus. 3) In the ventral medulla, the superior salivatory nucleus, retrotrapezoid nucleus, compact and external formations of the nucleus ambiguous, A1 and caudal C1 catecholamine neurons, and caudal pressor area receive dense axonal projections, generally exceeding the PVH projection to the rostral C1 region. 4) The medial nucleus of the solitary tract (including A2 noradrenergic and aldosterone-sensitive neurons) receives the most extensive projections of the PVH, substantially more than the dorsal vagal nucleus or area postrema. Our findings suggest that the PVH may modulate a range of homeostatic functions, including cerebral and ocular blood flow, corneal and nasal hydration, ingestive behavior, sodium intake, and glucose metabolism, as well as cardiovascular, gastrointestinal, and respiratory activities.

[Deep brain stimulation and gait disorders in Parkinson disease]

INTRODUCTION

Gait disorders and freezing of gait (FOG) are seen in most patients with advanced Parkinson disease. Response to levodopa and deep brain stimulation is variable across patients.

STATE OF ART

Thalamic stimulation is ineffective on gait and can even worsen balance when bilaterally applied. Pallidal stimulation moderately improves gait disorders and FOG although this effect tends to wane after three to five years. Stimulation of the subthalamic nucleus (STN) improves levodopa-responsive gait disorders and FOG. However, some patients worsen after STN stimulation and others are better improved under levodopa than under STN stimulation. Synergistic effects of the two treatments have been reported. As for pallidal stimulation, there is a failure of long-term STN stimulation to improve gait, probably due to the involvement of non-dopaminergic pathways as the disease progresses. Levodopa-resistant gait disorders and FOG do not usually benefit from STN stimulation. In the rare cases of levodopa-induced FOG, STN stimulation may be indirectly effective, as it enables reduction or arrest of the levodopa treatment.

PERSPECTIVES

Pedunculopontine nucleus stimulation has recently been performed in small groups of patients with disabling gait disorders and FOG. Although encouraging, the first results need to be confirmed by controlled studies involving larger series of patients.

CONCLUSIONS

Overall, gait disorders remain a motor PD symptom that is little improved, or only temporarily, by current pharmacological and surgical treatments. Patient management is complex.

Deep brain stimulation effect on freezing of gait

The majority of patients with Parkinson's disease suffer from freezing of gait (FOG), which responds more or less to levodopa. Thalamic stimulation, mainly used in the treatment of tremor dominant Parkinson's disease is ineffective in FOG. GPi stimulation moderately improves FOG, but this effect may abate in the long term. STN stimulation was reported to improve levodopa-responsive FOG. In some patients, the benefit from levodopa is greater than that from STN stimulation, and levodopa and STN stimulation can have additive effects. On the contrary, STN stimulation is ineffective on levodopa-resistant FOG. In the few cases of levodopa-induced FOG, STN stimulation can indirectly be effective, thanks to a great decrease or arrest of levodopa. Stimulation of the pedunculopontine nucleus has recently been performed in small groups of patients suffering from both off- and on-levodopa gait impairments. The first results appear encouraging, but they need to be confirmed by controlled studies in larger series of patients.

Inputs to the ventrolateral bed nucleus of the stria terminalis

The ventrolateral bed nucleus of the stria terminalis (BSTvl) receives direct input from two specific subpopulations of neurons in the nucleus tractus solitarius (NTS). It is heavily innervated by aldosterone-sensitive NTS neurons, which are selectively activated by sodium depletion, and by the A2 noradrenergic neurons, which are activated by visceral and immune- and stress-related stimuli. Here, we used a retrograde neuronal tracer to identify other brain sites that innervate the BSTvl. Five general brain regions contained retrogradely labeled neurons: cerebral cortex (infralimbic and insular regions), rostral forebrain structures (subfornical organ, organum vasculosum of the lamina terminalis, taenia tecta, nucleus accumbens, lateral septum, endopiriform nucleus, dorsal BST, substantia innominata, and, most prominently the amygdala--primarily its basomedial and central subnuclei), thalamus (central medial, intermediodorsal, reuniens, and, most prominently the paraventricular thalamic nucleus), hypothalamus (medial preoptic area, perifornical, arcuate, dorsomedial, parasubthalamic, and posterior hypothalamic nuclei), and brainstem (periaqueductal gray matter, dorsal and central superior raphe nuclei, parabrachial nucleus, pre-locus coeruleus region, NTS, and A1 noradrenergic neurons in the caudal ventrolateral medulla). In the arcuate hypothalamic nucleus, some retrogradely labeled neurons contained either agouti-related peptide or cocaine/amphetamine-regulated transcript. Of the numerous retrogradely labeled neurons in the perifornical hypothalamic area, few contained melanin-concentrating hormone or orexin. In the brainstem, many retrogradely labeled neurons were either serotoninergic or catecholaminergic. In summary, the BSTvl receives inputs from a variety of brain sites implicated in hunger, salt and water intake, stress, arousal, and reward.

Bilateral pedunculopontine nuclei strokes presenting as freezing of gait

The penduculopontine nucleus (PPN) has been suggested to play an important role in locomotion, based on animal studies, but its function in humans has not been well defined. Autopsy studies have suggested that PPN pathology correlates with gait dysfunction in Parkinson's disease and in progressive supranuclear palsy but direct clinical evidence is lacking. We report a patient with bilateral PPN infarcts whose dominant clinical feature was freezing of gait, thus providing evidence that PPN is involved in human locomotion and that damage to the PPN may lead to abnormal gait.

Higher level gait disorders

Higher level gait disorders are common in the elderly. The pathophysiology of these gait disorders is poorly understood, and the nomenclature used to describe them is confusing and the subject of ongoing debate. It is suggested that higher level gait disorders can be explained in terms of breakdown in the organization of equilibrium and locomotion.

Podokinetic after-rotation in Parkinson disease

Walking on a rotating platform for 15 min causes healthy subjects to involuntarily turn when walking without vision. This adaptive response, called podokinetic after-rotation (PKAR), uses the same kinematic patterns as voluntary turning suggesting that PKAR and voluntary turning share common mechanisms. The purpose of this study is to determine whether people with Parkinson disease (PD), a condition that produces substantial disability from turning difficulties, can adapt to the rotating platform. Initial testing of people with PD revealed that most were unable to step on the rotating platform for 15 continuous minutes. We thus tested a less intense version of the paradigm in eight healthy people. On one day, subjects walked on the platform for 15 continuous minutes; on another day, they walked on the platform for three 5-minute intervals separated by 5-minute rests. After both sessions, subjects rested for 5 min then walked in place for 30 min without vision, while we recorded rotational velocity of PKAR. Continuous and interval protocols effectively elicited robust PKAR. We then tested eight subjects with PD and matched controls using the 5-minute interval protocol and recorded PKAR responses for 10 min. There were no significant differences between the PD and control groups. We conclude that PD subjects can adapt to the rotating platform and develop PKAR from interval training. Future studies are needed to determine whether the rotating platform may act as a rehabilitative tool to reinforce motor patterns for turning and alleviate turning difficulties in people with PD.

Ventriculoperitoneal Shunting of Idiopathic Normal Pressure Hydrocephalus Increases Midbrain Size: A Potential Mechanism for Gait Improvement

OBJECTIVE:

Idiopathic normal pressure hydrocephalus (INPH) is characterized by a classic clinical triad of symptoms, including dementia, urinary incontinence, and gait disturbance. Recent work has demonstrated that the maximal midbrain anteroposterior (AP) diameter is significantly smaller in patients with INPH than in healthy, age-matched controls. The current study was undertaken to determine the effect of ventriculoperitoneal shunt placement on midbrain dimensions in INPH patients.

METHODS:

Twelve consecutive INPH patients undergoing ventriculoperitoneal shunt placement with pre- and postoperative computed tomographic scans at the Columbia University Medical Center were enrolled. Each patient's pre- and postoperative maximum AP and left-to-right diameters of the midbrain at the pontomesencephalic junction were independently measured in a blinded fashion by two of the authors. The average value of each dimension was computed by calculating the mean values of the measurements of the two observers.

RESULTS:

Both the mean AP diameter (preoperative mean, 2.06 ± 0.04 cm; postoperative mean, 2.27 ± 0.05; P = 0.0007) and left-to-right diameter (preoperative mean, 2.80 ± 0.07; postoperative mean, 3.03 ± 0.08; P = 0.0029) increased from pre- to postoperative imaging. The approximate cross-sectional area determined as the product of AP and left-to-right diameters also increased from pre- to postoperative images (preoperative mean, 5.79 ± 0.22 cm2; postoperative mean, 6.90 ± 0.25 cm2; P = 0.00049).

CONCLUSION:

This study provides supportive evidence that midbrain cytoarchitecture may play a role in the pathophysiology and post-ventriculoperitoneal shunt gait improvement of INPH patients.