Abhishek Lenka

Abhishek Lenka
Baylor College of Medicine | BCM

MBBS, PhD (Clinical Neurosciences)

About

102
Publications
10,322
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,192
Citations
Citations since 2017
84 Research Items
1151 Citations
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
Introduction
Abhishek Lenka works in the Parkinson's Disease Center and Movement Disorders Clinics at the Baylor College of Medicine, Houston, TX. He completed his Neurology residency in the combined training program of Georgetown University & NIH/NINDS, Washington, DC, and Ph.D. (Neurosciences) from NIMHANS, Bangalore, India. His areas of research/clinical interest are PD-Psychosis, dysautonomia in Lewy body diseases, tremor pathophysiology, & advanced deep brain stimulation (DBS) programming.

Publications

Publications (102)
Article
Objective: Psychosis is one of the most debilitating complications of Parkinson disease (PD). Although research on PD psychosis has been focused on the study of well-structured visual hallucinations (VH), currently accepted National Institute of Neurological Disorders and Stroke-National Institute of Mental Health diagnostic criteria emphasize min...
Article
Objective The objective of the current study was to compare the microstructural integrity of the white matter (WM) tracts in patients having Parkinson disease (PD) with and without psychosis (PD-P and PD-NP) through diffusion tensor imaging (DTI). Methods This cross-sectional study involved 48 PD-NP and 42 PD-P who were matched for age, sex, and e...
Article
BACKGROUND Parkinson's disease with orthostatic hypotension (PD+OH) can be difficult to distinguish clinically from the parkinsonian form of multiple system atrophy (MSA‐P). Previous studies examined cardiac sympathetic neuroimaging to differentiate PD from MSA but without focusing specifically on PD+OH vs. MSA‐P, which often is the relevant differ...
Article
Full-text available
Tremor is the most commonly encountered movement disorder in clinical practice. A wide range of pathologies may manifest with tremor either as a presenting or predominant symptom. Considering the marked etiological and phenomenological heterogeneity, it would be desirable to develop a classification of tremors that reflects their underlying pathoph...
Article
Full-text available
Tremor is an involuntary, rhythmic, oscillatory movement of a body part. It is a central feature of a range of diseases resulting from pathological changes in the cerebellum. Interestingly, in modern times, the terms “cerebellar tremor” and “intention tremor” are often used synonymously and interchangeably. However, “cerebellar tremor” (i.e., tremo...
Article
Introduction: Although there has been substantial progress in research and innovations in symptomatic treatments, similar success has not been achieved in disease-modifying therapy (DMT) for Parkinson’s disease (PD). Considering the enormous motor, psychosocial and financial burden associated with PD, safe and effective DMT is of paramount importan...
Conference Paper
Background: A recently proposed “brain-first/body-first” dichotomy model of disease progression in Parkinson’s disease (PD) claims that Lewy body (LB) pathologies can begin either in the brain or in the body and progress in opposite rostro-caudal or caudal-rostral directions. Testing this model requires longitudinal follow-up of patients using obje...
Chapter
Tourette syndrome (TS) is a childhood-onset complex neurobehavioral disorder. The defining feature of TS is the presence of tics, which are described as sudden-onset, recurrent, brief-lasting, irregular, involuntary movements (motor tics) or sounds (phonic tics). Most patients with TS also have a variety of comorbid behavioral disorders, particular...
Article
Purpose of the review: Orthostatic hypotension (OH) is the primary manifestation of cardiovascular autonomic dysfunction in Parkinson’s disease (PD) and can be a prodromal feature of the disease. We review the recent progress in the field of autonomic dysfunction in PD. Recent findings Individuals with isolated neurogenic OH should be followed up...
Article
BACKGROUND: There is definite evidence for the involvement of retina in Parkinson's disease (PD). However, a specific pattern has not been clear due to the cross-sectional nature of the majority of the previous studies. OBJECTIVE: The aim of this work was to study the pattern of changes in the retinal layers in patients with PD on longitudinal fol...
Article
INTRODUCTION: Levodopa is the most effective medication for the treatment of motor symptoms of Parkinson’s disease (PD). Several factors may affect the efficacy and tolerability of levodopa. These include the timing, dosage and administration of levodopa, concomitant drugs, food, PD-associated non motor symptoms, and various neurologic and non-neu...
Preprint
Full-text available
Background Psychotic symptoms occur in a majority of schizophrenia patients, and in approximately 50% of all Parkinson’s disease (PD) patients. Altered grey matter (GM) structure within several brain areas and networks may contribute to their pathogenesis. Little, however, is known about transdiagnostic similarities when psychotic symptoms occur in...
Article
OBJECTIVES: To highlight the clinical significance of de novo dystonia and its spontaneous resolution during pregnancy. METHODS: Two patients were evaluated in a movement disorder clinic during their first trimester of pregnancy and followed up longitudinally. RESULTS: Our first patient developed severe right torticollis and laterocollis during the...
Article
Full-text available
BACKGROUND: A multimodal connectomic analysis using diffusion and functional MRI can provide complementary information on the structure–function network dynamics involved in complex neurodegenerative network disorders such as Parkinson’s disease (PD). Deep learning-based graph neural network models generate higher-level embeddings that could captur...
Article
Tacrolimus treatment is associated with a range of neurological adverse effects. Neurotoxicity caused by tacrolimus may result in subacute onset of tremor in a subset of patients. The commonly reported tremor phenomenology associated with tacrolimus neurotoxicity is the action tremor of bilateral upper limbs with or without rest tremor. Tremor may...
Article
Full-text available
BACKGROUND: There are few medications for the treatment of essential tremor (ET). One of these, primidone, which is one of only two front-line agents, is associated with considerable adverse drug reactions (ADRs). It is unclear why some primidone-treated ET patients develop ADRs whereas others do not, and why these ADRs seem to be more prevalent in...
Article
Full-text available
BACKGROUND: Task-specific dystonia (TSD) is a form of focal dystonia that occurs in the context of the performance of selective, highly-skilled, often repetitive, motor activity. TSD may be apparent during certain tasks such as writing, playing musical instruments, or other activities requiring fine motor control, but may also occur during certain...
Article
Purpose of the review To highlight five new things in the research and clinical aspects of essential tremor (ET). Recent findings The introduction of a new definition of ET and a new category “ET plus” were the major themes of the recent consensus statement. This new change demands a change in the approach to the clinical diagnosis of ET and relat...
Article
INTRODUCTION: Psychosis is one of the incapacitating non-motor symptoms of Parkinson’s disease (PD). Although several risk factors that include older age, rapid eye movement sleep (REM) behavior disorder (RBD), depression, and cognitive dysfunction have been identified, the exact neural correlates remain elusive. As cognitive impairment has a close...
Conference Paper
Background: After recovery from COVID-19, a substantial proportion of individuals with post-acute SARS-CoV2 (PASC) have persistent neurological problems that may include (1) fatigue, (2) ‘‘brain fog,’’ and (3) cardiovascular dysautonomia, manifested by excessive orthostatic tachycardia, lightheadedness, or a tendency to faint. We conducted comprehe...
Conference Paper
Background: Parkinson’s disease with orthostatic hypotension (PD+OH) can be difficult to distinguish clinically from the parkinsonian form of multiple system atrophy (MSA-P). Previous studies examined cardiac sympathetic neuroimaging to differentiate PD from MSA but without focusing specifically on PD+OH versus MSA-P, which often is the relevant di...
Article
The synucleinopathies Parkinson disease (PD), multiple system atrophy (MSA), and pure autonomic failure (PAF) are characterized by intra‐cytoplasmic deposition of the protein alpha‐synuclein and by catecholamine depletion. PAF, which manifests with neurogenic orthostatic hypotension (nOH) and no motor signs of central neurodegeneration, can evolve...
Article
A man in his early 60s with a medical history of granulomatosis with polyangiitis (GPA) in remission for two decades without maintenance therapy presented with non-specific complaints of profound fatigue and 40-pound weight loss. He was seronegative for antinuclear antibodies and cytoplasmic antineutrophilic antibodies, but erythrocyte sedimentatio...
Article
Full-text available
Objective Lewy body (LB) synucleinopathies such as Parkinson’s disease (PD) entail profound cardiac norepinephrine deficiency. The status of sympathetic noradrenergic innervation at other extracranial sites has been unclear. Although in vivo neuroimaging studies have indicated a cardioselective noradrenergic lesion, no previous study has surveyed p...
Article
Essential tremor (ET) is among the common movement disorders. A surge in research in recent years has considerably improved our understanding of disease etiology and pathogenesis, and its associated clinical phenomenology and natural history. With this progress have emerged a multitude of new questions and conundrums and newly proposed terminologie...
Article
Full-text available
Essential tremor (ET) is among the most prevalent neurological diseases. Appreciation in recent years of a richer tremor phenomenology, additional motor and non-motor features, variability in the natural course of tremor, associations with a host of other neurological conditions, and etiological and pathophysiological heterogeneity have resulted in...
Article
Full-text available
Essential tremor (ET) is among the most prevalent neurological diseases. Appreciation in recent years of a richer tremor phenomenology, additional motor and non-motor features, variability in the natural course of tremor, associations with a host of other neurological conditions, and etiological and pathophysiological heterogeneity have resulted in...
Article
Introduction: Handwriting is a complex activity involving cognitive, kinaesthetic and perceptual-motor components playing a critical role in the context of assessing neurodegenerative disorders. Difficulties in handwriting can be related to the disease and its severity which can serve as a prominent biomarker. This study proposes a methodology to m...
Article
Patients with Parkinson’s disease (PD) may undergo several elective and emergency surgeries. Motor fluctuations, presence of a wide range of non-motor symptoms, and the use of several medications, often not limited to dopaminergic agents, makes the perioperative management of PD challenging. However, the literature on perioperative management of PD...
Article
Sleep disturbance is one of the commonly reported non-motor symptoms in patients with Parkinson's disease (PD) as well as in Parkinson plus disorders such as multiple system atrophy (MSA), dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), and corticobasal syndrome (CBS). Although there is a wealth of literature on sleep disturb...
Article
Full-text available
Psychosis is a common and often debilitating non-motor symptom of Parkinson’s disease (PD). It typically manifests in the form of well-formed visual hallucinations and minor hallucinations, and, at times, can present with delusions and nonvisual hallucinations. Psychosis is associated with many adverse outcomes in PD, and for that reason, it is ess...
Chapter
Corticobasal degeneration is 1 of the atypical parkinsonian syndromes or Parkinsonism-plus syndromes that can mimic Parkinson disease, but it is distinct because of the added features of apraxia, dysphasia, cortical sensory signs, unusual dystonic postures, involuntary movements such as myoclonus, and “alien limb” sign. In this clinical article the...
Conference Paper
Objective: Psychosis is one of the debilitating non-motor symptom of Parkinson’s disease (PD) which commonly manifests through minor hallucinations (such as passage hallucinations, presence hallucinations, and illusions) and well-formed visual hallucinations. Cognitive impairment is strongly associated with psychosis in PD (PD-P). This study aimed...
Article
Abstract: OBJECTIVE: The objective of this study was to evaluate the gray matter (GM) volume alterations in different clinical stages of Parkinson’s disease (PD) through voxel-based morphometry (VBM). BACKGROUND: Assessment of the clinical stages of PD is usually carried out using the Hoehn and Yahr (H–Y) scale. However, there is paucity of litera...
Article
It is commonly thought that visuomotor adaptation is mediated by the cerebellum while reinforcement learning is mediated by the basal ganglia. In contrast to this strict dichotomy, we demonstrate a role for the basal ganglia in visuomotor adaptation (error‐based motor learning) in patients with Parkinson's disease (PD) by comparing the degree of mo...
Article
Background: West Nile virus (WNV) is a flavivirus that is recognized as one of the common causes of arboviral neurological disease in the world. WNV infections usually manifest with constitutional symptoms such as fever, fatigue, myalgia, rash, arthralgia, and headache. Neuroinvasive WNV infections are characterized by signs and symptoms suggestiv...
Article
Optical coherence tomography (OCT) has been evaluated as a tool to assess retinal changes in various neurodegenerative disorders. Parkinson’s disease (PD), is a neurodegenerative disorder wherein dopaminergic deficiency results in some of the symptoms. As retina also has high concentration of dopamine, it would be of interest for both the clinician...
Article
Introduction: Cervical dystonia is the most common focal dystonia encountered in a movement disorders clinic. It may have a huge impact on patients’ quality of life due to involuntary movement and abnormal posture of the head, neck pain, limitations in the range of neck movements, and psycho-social stress. Botulinum toxin is the preferred treatment...
Article
Full-text available
OBJECTIVES: To compare the sleep profiles of genetically proven cases of Huntington’s disease (HD) with healthy controls and to correlate the results of various sleep-related parameters with disease severity, duration, and length of cytosine–adenine–guanosine repeats. METHODS: This prospective study was conducted at the National Institute of Mental...
Preprint
Full-text available
It is commonly thought that visuomotor adaptation is mediated by the cerebellum while reinforcement learning is mediated by the basal ganglia. In contrast to this strict dichotomy, we demonstrate a role for the basal ganglia in visuomotor adaptation (error-based motor learning) in patients with Parkinsons disease (PD) by comparing the degree of mot...
Article
Objectives The present study was undertaken to evaluate the cognitive profile of Parkinson’s disease (PD) patients with REM sleep behavior disorder (RBD) and to correlate with the clinical stage and polysomnographic variables. Methods The study included 25 PD patients who had RBD and 25 PD patients who based on two questionnaires were determined a...
Article
Background: Essential tremor (ET) is reported to have a bimodal distribution of age at onset (AAO) with phenotypic variability based on the AAO. This study aims to explore the distribution of AAO based on mathematical modeling and ascertain the differences, if any, in the clinical features of groups. Methods: A chart review was conducted for 252...
Article
Tremor is a key clinical feature of several common neurological disorders. Adequate management of tremor has been an unmet need in clinical practice. Most of the anti-tremor medications have limited efficacy and are associated with undesirable adverse effects, especially in elderly patients. Several studies have reported good outcomes with the use...
Article
Full-text available
Patients with Parkinson’s disease (PD) develop a range of non-motor symptoms (NMS). Sleep disturbance is one of the common NMS of PD and the onset of sleep disorders often precede the onset of motor symptoms of PD. Motor symptoms of PD often receive the main clinical focus and the sleep disturbances often go unnoticed in clinical practice. Given th...
Article
Background: Freezing of gait (FOG) is a common and debilitating symptom in Parkinson's disease (PD); the pathogenesis and natural course of which has not been fully understood. Objectives: This study was performed to evaluate patients with FOG in PD and ascertain factors contributing to an early onset of FOG in patients with PD. Methodology: A char...
Article
Background Freezing of gait (FOG) is a common and debilitating symptom in Parkinson's disease (PD); the pathogenesis and natural course of which has not been fully understood. Objectives This study was performed to evaluate patients with FOG in PD and ascertain factors contributing to an early onset of FOG in patients with PD. Methodology A chart...
Article
Full-text available
Psychosis, manifested through formed visual hallucinations or minor hallucinations, is a common non-motor symptom of Parkinson’s disease (PD). The pathogenesis of psychosis in PD remains unclear; however, is possibly linked to structural and functional alterations in the hippocampus. To explore the role of hippocampus in psychosis, a detailed hippo...
Article
Improvement in motor symptoms with levodopa is one of the hallmark features of Parkinson’s disease (PD). The response to levodopa may reduce during the course of the illness. Few studies have also reported reduced response to levodopa in patients with PD several years after deep brain stimulation (DBS) of the subthalamic nucleus (STN) on both the s...
Article
Background: To investigate the diagnostic utility of signal intensity measurement of the substantia nigra pars compacta (SNc) using three dimensional (3D) neuromelanin-sensitive 31MRI, for discrimination of patients with PD from healthy controls. Methods: T1-weighted neuromelanin sensitive images of 16 patients with PD and 15 controls were quant...
Article
Background: Recent advances in neurophysiological techniques have contributed to our understanding of the pathophysiology of Huntington's disease (HD). Studies of the motor cortical excitability and central motor pathways have shown variable results. Objectives: Our aims were to evaluate the cortical excitability changes in HD using transcranial...
Article
Full-text available
Background: Orthostatic tremor (OT), a rare and complex movement disorder, is characterized by rapid tremor of both legs and the trunk while standing. These disappear while the patient is either lying down or walking. OT may be idiopathic/primary or it may coexist with several neurological conditions (secondary OT/OT plus). Primary OT remains an en...
Article
INTRODUCTION: Dystonia is one of the most prevalent forms of movement disorders and is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. Dystonia causes significant morbidity with an adverse impact on the quality of life. When dystonia is medically refractory, causing se...
Article
Introduction Patients with Parkinson’s disease (PD) may develop several non-motor symptoms (NMS). Psychosis is one of the debilitating NMS of PD. The neurobiology of psychosis is not fully understood. This study aims to compare the frontal lobe functions of PD patients with and without psychosis using the Frontal Assessment Battery (FAB). Methodol...
Article
Full-text available
Background: Writer’s cramp (WC) is one of the commonly observed focal dystonias. The pathophysiology of WC has not been fully understood. The role of the cerebellum has been increasingly recognized in the pathogenesis of dystonia. As the cerebellum is crucial for maintaining accurate eye–hand coordination (EHC), its role in the pathogenesis of WC c...
Article
Full-text available
Background: Essential tremor (ET) is the most common tremor disorder. In addition to its hallmark feature, kinetic tremor of the upper limbs, patients may have a number of non-motor symptoms and signs (NMS). Several lines of evidence suggest that ET is a neurodegenerative disorder and certain NMS may antedate the onset of tremor. This article compr...
Article
Full-text available
PurposePrimary writing tremor (PWT) is a rare task-specific tremor, which occurs only while writing or while adopting the hand in the writing position. The basic pathophysiology of PWT has not been fully understood. The objective of this study is to explore the alterations in the resting state functional brain connectivity, if any, in patients with...
Article
Full-text available
Background: Involvement of the central nervous system in patients with syphilis (neurosyphilis) may result in several neuropsychiatric symptoms. Rarely, patients with neurosyphillis may develop movement disorders with different phenomenology. Subtle orofacial dyskinesias have been reported in patients with neurosyphilis, known as the candy sign. Ca...
Article
Background: Majority of the patients with Parkinson’s disease (PD) have handwriting abnormalities. Micrographia (abnormally small letter size) is the most commonly reported and easily detectable handwriting abnormality in patients with PD. However, micrographia is perhaps the tip of the iceberg representing the handwriting abnormalities in PD. Digi...
Article
Introduction: Psychosis is one of the common non-motor symptoms of PD, which substantially worsens the quality of life. Hence, it is important to identify factors that are associated with early onset of psychosis in PD. In order to identify those factors, the current study aims to compare various demographic and clinical features of PD patients wit...
Article
Background and purpose: The objective of this work was to investigate whether patients with and without freezing of gait (FOG) in Parkinson's disease (PD) have differences in iron accumulation in substantia nigra using R2* relaxometry. Materials and methods: This study included seventeen PD patients with FOG [FOG (+)], equal number of age and gende...
Article
Full-text available
Objective: To determine the diagnostic characteristics of poor visualisation of nigrosome-1 as a neuroimaging biomarker in Parkinson's disease (PD) and to explore the relationship of poor visualisation of nigrosome-1 and clinical asymmetry. Methods: High-resolution gradient-echo sequences of 67 patients with PD and 63 healthy controls were revie...
Chapter
Nonmotor symptoms (NMS) are recognized to profoundly affect the quality of life of patients with Parkinson's disease (PD) and of their caregivers. In order to further understand the underlying pathophysiology, clinical presentation, response to medication, and prognosis, it is important to identify and analyze possible factors, which have an impact...
Article
Full-text available
Background: Although essential tremor (ET) is the most common tremor disorder, its pathogenesis is not fully understood. The traditional model of ET, proposed in the early 1970s, posited that the inferior olivary nucleus (ION) was the prime generator of tremor in ET and that ET is a disorder of electrophysiological derangement, much like epilepsy....
Article
Patients with Parkinson's disease (PD) may develop a wide spectrum of non-motor symptoms during the course of illness. Psychosis is one such commonly observed non-motor symptoms of PD. Although several studies based on neuroimaging, genetics, retinal imaging, and neuropsychological evaluations have explored the pathogenesis of psychosis in PD; exac...
Article
Full-text available
Parkinson's disease (PD) is a neuro-degenerative disorder, which predominantly affects the motor system. Diffusion MRI has demonstrated deficits in anisotropy as well as increased diffusivity in the sub-cortical structures, primarily in the substantia nigra in PD. However, the clinical spectrum of PD is not limited to motor symptoms, rather it enco...
Article
Background and objective Progressive Supranuclear Palsy (PSP) is a progressive neurodegenerative disorder. Classic PSP or Richardson-Steele phenotype (PSP-RS) and parkinsonian phenotype (PSP-P) are the common subtypes of PSP. At the early stage, differentiating the subtypes of PSP as well as differentiating PSP from other parkinsonian disorders, es...
Chapter
Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. The prevalence of PD increases with age. The spectrum of clinical features, the rate of progression of the disease, the burden of nonmotor symptoms, and the response to medications are different in older patients with PD from the relatively youn...
Article
Full-text available
Introduction: Essential tremor (ET) is the most common movement disorder among adults. Although ET has been recognized as a mono-symptomatic benign illness, reports of non-motor symptoms and non-tremor motor symptoms have increased its clinical heterogeneity. The neural correlates of ET are not clearly understood. The aim of this study was to unde...
Article
Progressive supranuclear palsy (PSP) is a progressive neurological disorder characterized by presence of supranuclear gaze palsy, early postural instability, parkinsonism and cognitive impairment. Advanced structural neuroimaging studies have demonstrated variable areas of grey and white matter involvement in PSP. Grey matter (GM) involvement is pr...