Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults. The literature in this field supports the notion than many patients become candidates for surgery and little is known about the group of patients who do not require surgical treatment. This is a retrospective cohort study that included all patients with TLE assessed and followed by the Saskatchewan Epilepsy Program since 2007. Mild course was defined as patients not having seizures, using or not AEDs at last follow up. Severe course of TLE was considered in patients with continuous seizures and patients who had epilepsy surgery. Descriptive statistics were used. OR and CI were calculated. One hundred and fifty nine patients were included. Age of patients at last follow up was 46.04 + 14.4 (range 19-88) years. Mean follow up of patients was 43.46+ 22.6 (6 to 84) months. Fourth six patients (29%) were seizure-free with AEDS (mild course TLE) and 113 (61%) had severe course of TLE. Patients with mild course of TLE were older (p 0.002), with a late onset of epilepsy (p< 0.001) and their epilepsy evolution was shorter (p<0.001). Our study shows that not all the patients with TLE require surgery and that a fair percentage of patients can be controlled with medication.

Introduction: The mainstay of diagnosis in Idiopathic Epilepsies (IE) is the electroencephalogram (EEG). The characteristic EEG of each syndrome is an electrographic endophenotype of the larger clinical phenotype of each and more directly associated with potential gene defects than the full phenotype. Endophenotypes represents primary abnormalities elicited by the gene defect, which, in some patients, blossom into full seizures. Revealing the percentage of abnormal EEGs in asymptomatic relative of patients with IE may help to describe the mode of inheritance that would help the ongoing genetics studies to discover the pathologic gene defect. Method: This is a prospective cohort study to identify the percentage of abnormal EEG in asymptomatic first-degree relatives of patients with IE Results: 20 out of 141 EEGs (14%) of first-degree relatives were abnormal. The abnormalities included generalized polyspikes and waves , generalized 3-Hz spike and waves or centro-temporal spikes in 50% of the abnormal EEGs. 50% of the abnormalities were nonspecific. Conclusion: These results may indicate that the EEG endophenotypes in IEs do not follow a Mendelian pattern of inheritance. Nevertheless, the EEG endophenotype is relatively common and thus genetically simpler than the full epilepsy, which will aid in gene identification

Objective: “Epilepsy in the elderly (EE)” is considered a homogeneous, benign syndrome in patients aged > 60 years, with cerebrovascular disease as the most frequent etiology. We challenge this concept by comparing EE and middle-aged adults with epilepsy (MAE). Methods: We compared: 1) seizure dynamics, 2) MRI lesions, 3) EEG findings and 4) treatment course in EE and MAE at the Halifax First Seizure Clinic. Results: 48 EE patients aged > 60.2 years (median 66.9 years). 31 MAE patients aged 50.2 – 59.6 years (median 55.1 years). Seizure dynamics in EE/MAE included first seizure in 50/54.8%, new onset epilepsy (new seizures within 12 months) in 43.8/35.5%, newly diagnosed epilepsy (seizures for >> 12 months) in 9.6/6.3%. First seizure evolved into new onset epilepsy in 12.5/3.2%. MRI in EE/MAE was normal in 22.5/27.6% or showed microangiopathy (25/38.5%), atrophy (10/15.4%), tumors (7.5/11.5%), vascular malformations (7.5/3.8%), hippocampal pathologies (0/3.8%), infarcts (12.5/0%). EEG in EE/MAE was normal in 64.4/65.5% or showed diffuse (6.6/3.5%) or focal slowing (8.8/7%), generalized (4.3/13.7%) or focal (15.4/10.4%) epileptiform activity. At 12 months, 87% of EE and 93.8% of MAE were seizure-free. Conclusions: EE and MAE show similar heterogeneity. We propose an etiology-driven classification of epilepsy syndromes in the aging brain.

Background: Temporal Lobe Epilepsy is associated with bilateral gray (GM) and white matter (WM) loss. After surgical treatment progressive bilateral temporal and extra-temporal WM change occur, however, less is known regarding post-operative GM change. We set out to measure contralateral hippocampal volume (CHV) following TLS. Methods: 1.5T-3D-1mm-isotropic-MPRAGE scans in 26 TLE patients and 3 controls in two groups: longitudinal (n=10)(imaged POD1,2,3,6,60,120 and >360d) and single post-operative scan (n=16). Manual volumetry protocols. Results: We find significant CHV atrophy at delayed scan relative to baseline (mean atrophy 26.8%). In the longitudinal group there is significant and progressive atrophy from baseline to POD4-8 (72.6+/-6.5%), POD60-360 (69.7+/-12.3%) and >360 (58.5+/-10.6%). No significant atrophy in either the control group HV or contralateral CV over time. No significant difference in mean HV at the most delayed exam for surgery type (p=0.13) or side (p=0.24). Conclusions: We find a statistically significant CHV atrophy following surgery which is progressive over time. Our longitudinal within-subject design describes the time course and extent more fully than previous work. Caudate analysis indicates that early CHV atrophy is not due to global atrophy following brain surgery but rather may be due to deafferentation and deefferentation. Finally, we find no significant difference in atrophy when analyzed by surgical approach or surgical side.

Background: In Canada, marijuana is legal for those with seizures. We determined the prevalence of marijuana use in intractable epilepsy patients and assessed the perceived effects. Methods: Information about marijuana use was collected over 12 months from consecutive adult patients admitted to an 8 bed Epilepsy Monitoring Unit using a 27 item self-administered questionnaire. Patients unable to understand and give consent for participation were excluded. Results: 215 of 310 patients median age 36 (interquartile range 27-49) years, 57% female had proven epilepsy. Median duration of seizures was 12 years (interquartile range 5-24) occurring daily or weekly in 47%. 37% of patients used marijuana over the previous year, 85% by smoking and 56% on a daily basis. Mean dose was 1 gm/day. Another 19% had used it previously. Use of cigarettes was 27%, alcohol, 40% and street drugs 2%. Seizure improvement was perceived by 91%, decreased stress by 99%, improved sleep by 98% and reduction in antiepileptic drug side effects by 88%. Minor adverse effects of marijuana occurred in 13% including seizures worse in 3%. Conclusions: Patients investigated for intractable epilepsy use marijuana more than the general population and perceive improved seizure control, lower stress, better sleep and reduced side effects from antiseizure drugs.

Background: Caspr2 is a transmembrane protein facilitating intercellular communication. It is found primarily in the central nervous system, specifically cerebellum and hippocampus. Anti-Caspr2 antibodies, more commonly seen in men (M/F: 4), also bind voltage-gated potassium channels. The antibodies are associated with limbic encephalitis, seizures, Morvan’s syndrome, peripheral nerve hyperexcitability, and cerebellar ataxia. Malignancy exists in 20% of cases. Methods: Case report and review of literature. Results: A 71-year-old man presented with subacute onset refractory seizures failing several anti-convulsants, emotional lability, and rapid decline in memory and executive function. EEG showed an electrographic seizure over the left hemisphere. MRI brain demonstrated mild diffuse cerebral atrophy, chronic ischemic changes, and mild diffusion restriction in the medial frontal lobes. Cerebrospinal fluid was normal. Serum Antithyroid peroxidase and antithyroglobulin antibodies were negative. TSH was slightly elevated and eltroxin didn’t help. Anti-Caspr2 antibodies were highly positive. EMG ruled out neuromyotonia. Body CT and PET scans indicated no malignancy. Treatment with IVIG stopped the seizures and cognition dramatically improved. Conclusions: Recognizing anti-Caspr2 antibody-associated encephalitis in elderly males with new onset refractory epilepsy and rapid cognitive decline is important for timely initiation of immunomodulation to avoid permanent deficits. Rapid executive dysfunction was unique in this case.

Background: The goal of our project is to assess the feasibility of replacing the invasive Wada test considered as the gold standard with non-invasive fMRI test for assessment of language dominance preoperatively. Methods: fMRI test with three language paradigm tasks (verb generation, sentence completion and naming) were conducted on our cohort of patients. fMRI laterality indices (LI) were then defined as a ratio (L-R)/(L+R) between the number of activated voxels in the left and right ROIs for Anterior Language Area (ALA) and Posterior Language Area (PLA). fMRI results were divided into the right (LI < -0.2), left (LI > 0.2) or bilateral (-0.2 < LI <0.2) hemispheric language dominance and compared to the results of the Wada test. Results: 28 patients were studied. The concordance rate between Wada and fMRI tests for the ALA and PLA was 68.2% and 52.2% for sentence completion; 56% and 52% for verb generation and 25% and 35% for naming paradigm, respectively. Conclusions: Sentence completion and verb generation fMRI paradigms showed higher concordance with Wada test than naming paradigm. The higher discordance between the Wada test and fMRI was related to bilateral results suggestive of less stringent thresholds used for either test.

Background: Analysis of infraslow EEG activity (ISA) has shown potential in the evaluation of patients with epilepsy and in differentiating between focal and generalized epilepsies. The purpose of this report is to present a girl with Sturge-Weber Syndrome (SWS) who was identified to have infraslow status epilepticus (ISSE), which successfully resolved after Midazolam administration Methods: The continuous EEG recording of a 5-yr-old girl with known Structural Epilepsy due to Sturge-Weber is presented. The patient presented to the ED with acute confusion, eye deviation and right hemiparesis similar to two previous admissions. ltm-eeg showed diffuse slowing. DWI obtained within 72-hr showed no ischemic changes, analysis of the EEG nfraslow (ISA) activity was undertaken using LFF 0.01 AND HFF of 0.1 Hz respectively. Results: Continuous subclinical unilateral rhythmic ictal ISA was identified. This was only evident in the left hemisphere which correlated with the structural changes due to SWS. A trial of continuous IV midazolam resulted in immediate resolution of the contralateral hemiparesis and encephalopathy. Conclusion: Continuous prolonged rhythmic ictal Infraslow activity (ISA) can cause super-refractory subclinical focal status epilepticus. This has not previously reported, and we propose this should be called Infraslow status epilepticus (ISSE). ISA analysis should be performed in all patients with unexplained subclinical status epilepticus.

Background: Leptomeningeal Carcinomatosis (LMC) is defined as a diffuse or multifocal malignant infiltration of the Pia matter and arachnoid membrane. It is clinically diagnosed in 5-10% of all cancer patients. The most commonly reported cancers associated with LMC are breast, lung and hematological malignancies. Patients with LMC commonly present with multifocal neurological symptoms. Symptoms are related to increase intracranial pressure, hemispheric dysfunction, cranial neuropathies and spinal roots dysfunction. We report a case of LMC secondary to Gastroesophageal junction cancer present initially with Cauda equine syndrome. Methods: A 51 year old male patient with adenocarcinoma of Gastroesophageal junction who underwent surgical resection, chemotherapy and radiation therapy. Nine month after diagnosis he presented with left leg pain, mild weakness and saddle area numbness. Initial radiological examination were unremarkable. Subsequently he had worsening of his leg weakness, fecal incontinence and urine retention. Two days later he developed rapidly progressive cranial neuropathies including facial diplegia, sensorineural hearing loss, dysarthria and dysphagia. Results: MRI with and without contrast showed diffuse enhancement of leptomeninges surrounding the brain, spinal cord and Cauda equine extending to the nerve roots. Cerebrospinal fluid cytology was positive for malignant cells. Conclusion: In cancer patient with Cauda equina syndrome and absence of structural lesion on imaging, LMC should be considered.

Background: IVLBCL is potentially treatable but difficult to diagnose. Methods: A case of progressive leg weakness and sphincter dysfunction diagnosed only at autopsy. Results: A 72 year old female presented with three weeks of increasing leg weakness and three days of urine and stool incontinence. Electrophysiological testing showed reduced tibial and peroneal CMAPs, preserved sural SNAPs, and bilateral gastrocnemius fibrillations, consistent with a pre-ganglionic lesion. Lumbosacral MRI with gadolinium showed no abnormalities. CSF was examined three times (protein 1.18-1.25, glucose 2.6-3.1, normal cell count and cytology). Whole-body FDG PET scanning showed hypermetabolic foci at the tongue base and in the mediastinum, but biopsy of both revealed no abnormality. Leg weakness progressed over three months and spread to the arms despite a course of IVIg. Four months later she died of cardiorespiratory arrest. Autopsy revealed the presence of large atypical B-cells within the lumen of small and medium sized vessels in numerous organs. There was evidence of anterior spinal artery obstruction with lymphocytes and anterior horn infarction in the lumbar cord. Conclusions: Although the literature reports that IVLBCL responds well to chemotherapy, this patient illustrates the difficulty of ante-mortem diagnosis. Nerve root biopsy may be warranted in such patients.

Background: Postural tachycardia syndrome (POTS) is defined as heart rate (HR) increments ≥30 bpm on head-up tilt (HUT) associate with orthostatic symptoms (lightheadedness, dizziness, palpitations, etc.). A large proportion of asymptomatic young adults naturally express excessive HR increments on HUT, which has raised questions regarding whether revision to the diagnostic criteria for POTS in younger patient populations is needed. In addition, poor adaptation to environmental stressors may contribute to the disability experienced by POTS patients. Objectives: 1) determine whether asymptomatic patients were predisposed to developing constitutional symptoms that could result in the full syndrome of POTS, and 2) determine whether these symptoms correlated to postural HR or orthostatic symptoms. Methods: HR response to HUT and orthostatic and constitutional symptoms in 30 asymptomatic POTS patients were evaluated after 1 year. Results: HR increment at follow-up demonstrated no correlation with general fatigue (r = 0.006), body vigilance (r = 0.195), physical (r = -0.087) and mental (r = -0.137) health, or orthostatic scores (r = 0.04). Orthostatic scores significantly correlated with general fatigue (r = 0.374) and body vigilance (r = 0.392) (p<0.05). Conclusion: These data support that the majority of young individuals express benign orthostatic tachycardia and further argue for re-evaluation of the HR criteria for diagnosing POTS in younger populations.

Background: Valsalva maneuver (VM) is a simple and non-invasive technique extensively utilized clinically to detect dysautonomia. VM provides detailed information of baroreflex sensitivity (BRS) which is an important cardiovascular and autonomic marker. However, the current approach for calculating its adrenergic component (BRSa1) is moderately reliable and fails to evaluate atypical VM patterns. Methods: We analyzed typical and atypical VM patterns of 89 young, healthy individuals (30 ±13 years) with the aim of improving BRSa evaluation. Objectives: 1) To determine a new BRSa calculation (BRSa2) applicable to different VM patterns; 2) correlate BRSa2 to BRSa1; 3) compare the internal consistency (ICC) between BRSa1 and BRSa2. Results: The BRSa2 calculation is a complex hemodynamic and time assessment equivalent to the slope in vagal BRS. In contrast to BRSa1, BRSa2 operates with hemodynamic indices easily detectable in any VM pattern. In atypical VM patterns, BRSa2 correlated with BRSa1: “flat-top responses” (r = 0.774, p < 0.01); rapid hemodynamic recovery (r = 0.461, p < 0.05). Most importantly, BRSa2 was more reliable than BRSa1 (ICC= 0.759 versus 0.469). Conclusion: BRSa2 is more reliable and allows atypical responses to VM to be analyzed, which clinically, could help differentiate natural physiological variances and mild adrenergic dysfunction.

We present a 25 year old female veterinarian technician presenting with rapidly progressive quadriplegia in less then 12 hours. Her symptoms occurred at work with initially bilateral hand weakness followed by arm and leg weakness. Before the end of the day she was on a ventilator in the ICU. MRI showed a hyperintense longitudinal T2 signal extending from the cervical medullary junction to T1. Extensive cervical spinal cord edema with cord expansion was noted. CSF showed normal protein and cell count with no oligoclonal banding. A post-infectious inflammatory process causing transverse myelitis was presumed and she was given IVIG, steroids, and plasmapheresis with no improvement. A serum ELISA test for IgG to Toxocara was reactive at titre of 1:800 at 3 weeks after her initial presentation. Her serum IgE levels was elevated at 169 x 10x3 U/L (Normal <87 x 10x3 U/L). At 4 weeks, she was commenced on albendazole at 800 mg per day for two months. A repeat serum ELISA test at 6 weeks and 2 weeks into her treatment with albendazole showed a declining titre of 1:200 consistent with recent Toxocara infection. At 10 weeks, her ELISA test was non-reactive. Unfortunately she did not respond to albendazole treatment and she shows minimal improvement now 1.5 years later.

Idiopathic CD4 lymphopenia is a rare immune disorder that renders patients vulnerable to unusual infections. A 25-year-old female had been diagnosed with idiopathic CD4 lymphopenia (CD4 count of 50/uL) at age 14 after pulmonary infection with atypical mycobacterium, but had since been asymptomatic on Trimethoprim/Sulfamethoxazole prophylaxis. She presented now with 5 weeks of headache, vomiting, diplopia, and vertigo. This had been diagnosed as benign positional vertigo. However, neuro-ophthalmologic exam revealed gaze-evoked nystagmus, impaired smooth pursuit, a left hypertropic skew deviation, left sensorineural hearing loss, gait ataxia and left limb dysmetria. MRI brain showed a 15 mm extra-axial enhancing mass at the left cerebellopontine angle, and chest CT showed pulmonary lesions. CSF Cryptococcal antigen was highly positive (> 1:1024) and CSF culture grew Cryptococcus neoformans variety grubii. She was treated with amphotericin B 175 mg daily and 5-Flucytosine 1000 mg QID for 4 weeks, followed by Fluconazole 400 mg daily, and made an excellent recovery. Cryptococcal infection usually presents as a meningitis, but can occasionally present as a mass lesion. Cryptococcal infection is one of the most common complications in idiopathic CD4 lymphopenia. This case illustrates the importance of neurologic signs in correctly localizing the lesion and the need for high suspicion of serious pathology in patients with rare immune disorders.

Background: Ramsay Hunt Syndrome with cerebellar encephalitis is rare in adult. Case Report: We describe a 55-year-old diabetic female who presented with truncal ataxia, right peripheral facial palsy and right ear pain associated with erythematous vesicular lesions in her external auditory canal. Later, she developed dysmetria, fluctuating diplopia and dysarthria. No facial lesions were identified and lesions were limited to the external auditory canal. Cerebral spinal fluid tested positive for varicella zoster virus polymerase chain reaction. She was diagnosed with Ramsay Hunt Syndrome with spread to the central nervous system and treated with acyclovir intravenous therapy (10 mg/kg every 8 hours). Her facial palsy completely resolved within 48 hours of acyclovir treatment, however, vesicular lesions, imbalance and cerebellar symptoms remained; a tapering course of high dose prednisone was then added.

Discussion: Prognosis for facial palsy is poor in Ramsay Hunt Syndrome: Only 10% of patients will have complete resolution of their facial palsy. Improvement of facial palsy may be a good marker for response to treatment. Conclusion: Varicella zoster virus reactivation affecting the central nervous system in adults is rare. Knowledge of Ramsay Hunt syndrome with brainstem and/or cerebellar involvement is important for diagnosis and for consideration of antiviral and prednisone treatment.

Objective: To compare and contrast the observed versus predicted number of white blood cells (WBCs) in a traumatic cerebrospinal fluid (CSF) sample in children and adults. Background: Clinicians rely on a correction formula (Predicted_CSF_WBC=CSF_RBC×Blood_WBC/Blood_RBC) to determine if a true CSF leukocytosis exists. This formula may overestimate true CSF leukocytosis and lead to delayed treatment of meningitis. Methods: A retrospective review of CSF data of 105 patients who met the following criteria: 1) CSF from lumbar puncture (LP) contained≥1000 RBC/mm^3 and 2) CBC performed≤24 hours of LP; 3) negative CSF cultures. Regression analysis was performed to determine the relationship between actual and predicted CSF WBC values. Results: Regression modeling indicated a discrepancy in the predicted versus actual WBC values. Mean adult age was 48.9 years; CSF profile (mean WBC 146.3×10^6/L; RBC 17374×10^6/L; glucose 4.1 mmol/L; protein 1.4 g/L); mean peripheral WBC was 8.2×10^9/L; RBC 3.9×10^9/L. Mean pediatric age was 1.4 years; CSF profile (mean WBC 171.8x10^6/L; RBC 41763x10^6/L; glucose 2.7 mmol/L; protein 1.7 g/L); mean peripheral WBC was 12×10^9/L; RBC 7.2×10^9/L. Observed LP CSF WBC value was 47% of predicted (r^2=0.54 pediatric cohort; r^2=0.91 adults). Conclusion: True CSF leukocytosis could be missed in a traumatic CSF sample based on a currently applied correction formula. We propose the following modifcation: Observed_CSF_WBC=0.5x[CSF_RBC×Blood_WBC/Blood_RBC].

Background: The Alzheimer’s Disease Neuroimaging Initiative (ADNI) provides an opportunity to investigate the relationship between β-Amyloid neuropathology and patients’ long-term cognitive function change. We examined baseline 18F-florbetapir PET amyloid imaging status and 36-months’ change from baseline in cognitive performance in subjects with mild cognitive impairment (MCI). Method: The study included all ADNI subjects who underwent PET-imaging with 18F-florbetapir and had a clinical diagnosis of MCI at the visit closest to florbetapir imaging. β-Amyloid deposition was measured by florbetapir standard uptake value ratio (SUVR), and dichotomized as Aβ+(SUVR>1.1) or Aβ–(SUVR≤1.1). Cognitive scores, including ADAS11, MMSE and CDR sum of boxes (CDR-SB), were evaluated for up to 36 months. Results: Of 478 MCI-subjects who had at least one florbetapir scan, 153 had a cognitive evaluation at 36-month follow-up. Of those, 79 were Aβ– and 74 Aβ+. At 36-months, the Aβ+ vs. Aβ– group scores changed from baseline (LS means 4.03 vs. 0.26 for ADAS11; -2.61 vs.-0.40 for MMSE; 1.53 vs. -0.11 for CDR-SB [p< 0.0001 all comparisons]). Generalised estimating equation analysis on clinically significant cognitive change showed a marginal Odds Ratio=2.18 (95% CI: 1.47–3.21) for Aβ+ vs. Aβ– groups. Conclusion: MCI subjects with higher β-Amyloid deposition had greater deterioration in cognitive function over 36 months while subjects with no β-Amyloid accumulation tended to be stable.

Background: Opsoclonus can result from paraneoplastic, parainfectious, autoimmune, ischemic or toxic etiologies. Neuroinvasive complications develop in less than one percent of individuals infected with West Nile Virus. Methods: Case report. Results: A 63-year-old female presented with subacute disorientation, dizziness, oscillopsia, and unsteady gait, associated with fever. Examination demonstrated opsoclonus, bilateral upper extremity postural and action tremor and truncal ataxia. MRI of the brain was normal. CT of the body showed no evidence of neoplasia. Vasculitic and paraneoplastic panels were negative. An extensive infectious work-up was only positive for West Nile IgM antibodies. She was treated with clonazepam and received a five-day-course of IVIG. Her symptoms improved after treatment and she continued to demonstrate gradual recovery during the months following her discharge. Conclusions: There are only a few published case reports of WNV-associated opsoclonus, and our patient appears to be the oldest reported with this constellation of neurological symptoms. Even though treatment for WNV is mostly supportive, this case demonstrates the importance of a thorough work-up in patients of similar presentations to determine the etiology and to guide early immunomodulation in selected cases. Video available.

The objectives of the study were to analyze the association between Parkinson’s disease and restless legs syndrome, and explore the relationship between mood disorder comorbidity (anxiety and depression), pain, and restless legs syndrome. This study included 123 Parkinson’s disease patients and 123 healthy controls matched for age and gender, and evaluated for anxiety severity, depression severity, pain severity, pain interference, pain disability, and restless legs syndrome prevalence. This was performed using semi-structured interviews and a neurological examination. Restless Legs Syndrome diagnostic criteria and the following inventories were used; Hospital Anxiety and Depression Scale, Brief Pain Inventory, and Pain Disability Index. Parkinson’s disease patients had significantly greater anxiety severity, depression severity, pain severity, pain interference, pain disability, and restless legs syndrome prevalence in comparison to controls. In addition, Parkinson’s disease patients’ comorbid for anxiety and depression had significantly greater pain severity, pain interference, and pain disability, but not RLS prevalence, in comparison to Parkinson’s disease only, Parkinson’s disease anxiety, and Parkinson’s disease depression patients. Pain interference, pain severity, and pain disability is greater among Parkinson’s disease patients with anxiety and depression, in comparison to Parkinson’s disease patients without anxiety and depression. On the contrary, the prevalence of restless legs syndrome was not found to be relevant.

Objective of this study was assess the prevalence of Essential of Essential Tremor in Parkinson’s disease population Essential tremor (ET) is the most common movement disorders and is much more common than Parkinson’s disease, in general population. Essential Tremor and Parkinson’s disease (PD) tremor differ in type, frequency and distribution. Despite being two separate disorders, there have been cases reported of coexistence of ET-PD. Some studies have reported an increase in the incidence of ET in relatives of patients with PD, yet the risk of developing PD in ET patients has not been thoroughly investigated. Our study set out to determine the prevalence of precedent ET in PD patients. We conducted a retrospective chart review analysis of 332 idiopathic PD patients to determine how many of them had ET prior to the diagnosis of PD and the percentage of them who were also diagnosed with ET. Our results indicated that the prevalence of precedent ET among a population of idiopathic PD patients was not any higher than the prevalence of ET in a comparable general population. Our results support the notion that ET and PD are mutually independent disorders. Further studies are needed to understand the exact relationship between these two disorders