Evolution of coherence singularities in polarization singular beams.

The evolution of correlation singularities in partially coherent polarization singular beams (PC-PSBs) is investigated. Since PSBs are the superposition of two orthogonally polarized vortex beams, the occurrence of coherence singularities in PC-PSBs is strongly governed by the topological charge of the component vortex beams and the spatial coherence length. Coherence singularities appear in the form of ring dislocations in the modulus of the spectral degree of coherence (SDoC) profile, and the number of ring dislocations is equal to the higher value of the topological charge of the superposing vortex beam. Furthermore, the SDoC phase profile can be used to determine the polarity of a PC-PSB. The findings of the study could be valuable in various applications that rely on the spatial coherence of beams, such as free-space communication and imaging.

Successful stereoelectroencephalography re-evaluation in epilepsy patients after failed initial subdural grid evaluation.

OBJECTIVE: Epilepsy surgery success is dependent on accurate localization of the epileptogenic zone. Despite the use of invasive EEG using subdural grids and strips, surgical failures can occur. In this series, we explore the utility of a second evaluation with stereoelectroencephalography in patients whose initial invasive evaluation with subdural grid electrodes was unsuccessful in localizing seizure origin. METHODS: We conducted a retrospective review of patients who underwent subdural grid evaluation (SDE) at our center and identified patients who underwent a re-evaluation with stereoelectroencephalography (SEEG). RESULTS: We identified three patients who had both subdural and SEEG electrodes in the region of the identified epileptogenic zone in whom the initial SDE evaluation failed to make the patients seizure-free. Two of these patients underwent a second resection and became seizure-free. SIGNIFICANCE: Stereoelectroencephalography can be useful in the re-evaluation and re-operation of patients who previously had surgical failure using SDE.

Coherence-induced depolarization effects in polarization singular beams.

We demonstrate theoretically and experimentally coherence-induced depolarization effects in generic and higher index polarization singular beams endowed with C-point (or V-point) polarization singularity. The irradiance profiles and degree of polarization (DoP) distributions are found to be governed by spatial coherence length, polarization singularity index, and orbital angular momentum (OAM) of the superposition states of the beams. On reducing the coherence length, the DoP distribution in the V-point deteriorates uniformly. In contrast, C-point beams resist depolarization exhibiting anti-depolarization around the central core of the beam due to the nonzero net OAM of the beam. Interestingly, the polarization vortex structure remains preserved on reducing the spatial coherence length.

Investigation of partially coherent vector vortex beams with non-isotropic states of spatial correlation.

In this work, the far-field properties of non-isotropic partially coherent vector vortex beams (PCVVBs) are investigated both theoretically and experimentally. The term non-isotropic signifies that the spatial correlations between the parallel and orthogonal electric field components are distinguishable. It is found that self-orientation and shaping of intensity profile, correlation-induced polarization and depolarization are highly dependent on both the non-isotropic correlation parameters and Poincaré-Hopf index (PHI) of the beam. The simultaneous depolarization and polarization effects are due to the difference in the input correlation parameters that alter the state of polarization (SOP) and degree of polarization (DOP) distributions. The experimental results are in good agreement with the theoretical predictions. The distinguishability of correlation parameters at the source plane leads to significant changes on its intensity profile, DOP, and SOP distributions on far-field propagation, which may found potential applications in beam shaping, detecting and imaging atmospheric lidar, optical imaging and directional transportation where the self-rotation characteristic of beam plays an important role.

Young's double-slit experiment with vector vortex beams.

In this Letter, Young's double-slit experiment with vector vortex beams is investigated. We present the results for various Poincaré-Hopf index beams of this class considering all four major types. Polarization associated morphological changes in the far-field interference pattern are studied both theoretically and experimentally. The Fraunhofer pattern consists of lattices of polarization singularities of the generic type, located on a line, in a direction perpendicular to the slit. The number of linear lattices varies as a function of Poincaré-Hopf index η of the beam that is diffracted, and the number of intensity nulls occurring along the vertical line is equal to |η|.

A case of subependymal giant cell astrocytoma without tuberous sclerosis complex and review of the literature.

Subependymal giant cell astrocytoma (SEGA) is a World Health Organization (WHO) grade I tumor most commonly seen in the context of the underlying tuberous sclerosis complex (TSC). SEGA in the absence of TSC is exceedingly rare. We report the youngest known case of SEGA in the absence of genetic or phenotypic evidence of TSC with a 10-year follow-up. We discuss the literature surrounding isolated SEGA including an approach to diagnosis, management, and prognosis.

Coherence-induced polarization effects in vector vortex beams.

We demonstrate theoretically and experimentally coherence-induced polarization changes in higher-order vector vortex beams (VVBs) with polarization singularity. The prominent depolarization on decreasing the transverse correlation width in a focused partially coherent VVB provides a means to shape the intensity profile and degree of polarization (DOP) while preserving the polarization distribution. The intensity variation and DOP dip are found to be dependent on the polarization singularity index of the beam. Our results may provide an additional degree of freedom in myriad applications presently projected with VVBs.

Guillain-Barré syndrome and posterior reversible leukoencephalopathy syndrome: a rare association.

A 69-year-old woman presented with headaches and visual disturbance in the context of marked hypertension secondary to non-compliance with antihypertensive medications. She developed seizures and hyperreflexia, and MRI brain showed changes consistent with posterior reversible encephalopathy syndrome (PRES). She was treated with antihypertensives with the resolution of symptoms. Over the following week, she developed progressive distal sensory loss, weakness and areflexia. The cerebrospinal fluid examination demonstrated albuminocytologic dissociation, and electrophysiological findings were in keeping with a diagnosis of Guillain-Barré syndrome (GBS). She was treated with intravenous immunoglobulin with gradual recovery. The co-occurrence of PRES and GBS has only been described in a handful of cases. In the majority of these, the dysautonomia of GBS leads to profound hypertension and subsequently PRES. This is a rare case of PRES preceding and possibly even triggering the onset of GBS. In this report, we review the literature and discuss the potential pathogenic mechanisms for this unusual association.

Harding's disease: an important MS mimic.

Leber's hereditary optic neuropathy (LHON) is a mitochondrially inherited disorder characterised by bilateral, painless visual loss which leads to severe optic atrophy. It can be associated with other conditions including multiple sclerosis (MS), movement disorders, epilepsy and cardiac arrhythmias. The association of LHON with an MS-like illness is often referred to as Harding's disease (or Harding's syndrome). We report two siblings, who both harbour the 11 778 mitochondrial DNA (mtDNA) mutation, but who manifest markedly different clinical phenotypes; a male with classical LHON and a female with an MS-like illness. LHON affects males four to five times more often than females. By contrast, Harding's disease is seen predominantly in females, in a pattern comparable to that seen in MS. The pathogenic basis behind the variation in penetrance and phenotype between genders and individual family members remains unclear.

Guillain-Barré syndrome as a complication of hypertensive basal ganglia haemorrhage.

We aimed to study the potential relationship of Guillain-Barré syndrome (GBS) and intracranial haemorrhage (ICH). We present a case of a 70-year-old hypertensive woman who developed global weakness, eventually becoming quadriplegic, during an inpatient stay for treatment of a basal ganglia haemorrhagic stroke. Guillain-Barré syndrome was confirmed and treatment initiated. She responded well to intravenous immunoglobulin treatment and then subsequently continued with rehabilitation. There have been a few case reports of GBS as a complication of spontaneous intracranial haemorrhage (ICH) or traumatic brain injury. It may not be a coincidence that our patient developed GBS shortly after presentation. There may be an immunological explanation with immune activation following neuronal injury after ICH with associated blood-brain barrier breakdown. GBS following ICH adds further complexity to treating patients who are already critically ill. If patients develop new weakness after ICH, there should be a high index of suspicion for GBS. It should be distinguished from critical illness neuropathy/myopathy and other causes of weakness in critical care patients because the treatment is very different. Immune activation and sensitization to myelin-associated proteins may be the underlying pathophysiological basis.

Polarization-entangled photon generation using partial spatially coherent pump beam.

The generation of two photon fields, to date, has been demonstrated utilizing a fully coherent pump beam. In this paper we demonstrate, the theoretical and experimental generation of polarization entangled single photon pairs by varying the spatial coherence of the pump beam. The effect of the pump beam spatial coherence on the visibility of a polarization-entangled single photon source is investigated. A comparison of the visibility measurements using a fully coherent and partially coherent pump beam is performed. It is shown that the partial coherence of the pump beam contributes to an increase in the visibility. The coherence properties of the beam are significant for free-space optical transmission in particular for long range free-space quantum communication.

Transient oculomotor nerve palsy due to non-aneurysmal neurovascular compression.

Acute oculomotor nerve palsy requires urgent exclusion of aneurysmal compression. We report a 62year old man with a transient right third nerve palsy with pupillary involvement, who was found to have neurovascular compression of the cisternal oculomotor nerve as it curved over a duplicated superior cerebellar artery on high resolution MR imaging. Direct vascular compression should be considered in patients with isolated cranial neuropathies in whom other pathologies have been excluded.

Dystonic tics induced by deep brain stimulation of the posterior subthalamic area for essential tremor.

OBJECTIVE The posterior subthalamic area (PSA) is a promising target of deep brain stimulation (DBS) for medication-refractory essential tremor (ET). This case series describes a novel adverse effect manifesting as dystonic tics in patients with ET undergoing DBS of the PSA. METHODS Six patients with ET received electrode implants for DBS of the dorsal and caudal zona incerta subregions of the PSA. RESULTS Five of the 6 patients developed dystonic tics soon after clinical programming. These tics were of varying severity and required reduction of the electrical stimulation amplitude. This reduction resolved tic occurrence without significantly affecting ET control. Dystonic tics were not observed in 39 additional patients who underwent DBS of the same brain regions for controlling non-ET movement disorders. CONCLUSIONS The pathophysiology of tic disorders is poorly understood and may involve the basal ganglia and related cortico-striato-thalamo-cortical circuits. This series is the first report of DBS-induced tics after stimulation of any brain target. Although the PSA has not previously been implicated in tic pathophysiology, it may be a candidate region for future studies.

CADASIL mimicking multiple sclerosis: The importance of clinical and MRI red flags.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited small vessel disease, manifesting as recurrent ischaemic events, migraine with aura, behavioural disturbance and cognitive decline. We report two patients with CADASIL masquerading as multiple sclerosis (MS). A 23year old female presented with a visual scotoma and was discovered to have a corresponding retinal cotton wool spot. MRI brain revealed diffuse T2 hyperintensities suggestive of demyelination. A 56year old male presented with transient sequential paraesthesia, initially of the perineum followed by the right leg. He also reported memory and mood impairment with a history of migraine with aura. MRI of the brain showed diffuse bilateral white matter lesions with sparing of the anterior temporal poles. Both patients satisfied the modified McDonald diagnostic criteria and were initially thought to have MS. However, they did not satisfy the caveat of "no better explanation" and on subsequent testing NOTCH 3 mutations were identified in both patients [1]. These cases highlight the importance of careful clinical assessment and neuroimaging findings in identifying clinical and paraclinical 'red-flags' for a diagnosis other than MS.

Henoch-Schonlein purpura in mesothelioma.

Henoch-Schonlein purpura (HSP) is primarily a childhood immunoglobulin A (IgA)-mediated illness. When adults are affected, malignancy can be associated. We present a rare case of HSP in a 75-year-old man with malignant pleural mesothelioma. He presented with episodes of dizziness and subsequently developed non-palpable purpura across his legs, arthralgia, hematuria, proteinuria, and acute renal impairment. HSP was diagnosed based on clinical and histological findings on biopsy specimens from the skin and kidney that showed a leukocytoclastic vasculitis and mesangioproliferative glomerulonephritis with IgA deposits, respectively. He was treated with high-dose oral steroids with resolution of the skin and renal manifestations of the disease. HSP is rare in adults but has been linked to cancers. This is the first report of HSP in a patient with known malignant pleural mesothelioma.

Experimental observation of the effect of generic singularities in polychromatic dark hollow beams.

This Letter presents the essence of our recent experimental study on generic singularities carrying spatially partially coherent, polychromatic dark hollow beams (PDHBs). To the best of our knowledge, this is the first experimental demonstration of generic singularities-induced wavefront tearing in focused polychromatic beams.

Effect of surface plasmons on spectral switching of polychromatic light with Au-double-slit.

It is shown that the generation of surface plasmons on a metal-dielectric interface, i.e., a Au-double-slit and air interface, appreciably affects the intensity of the diffracted light. With a specific example of Au-double-slit and electro-optic devices before the slits, the spectral switching in the diffracted field with the polychromatic light is shown for the first time, to our knowledge. It is found that at the observation point due to the surface plasmon effect the intensity of the diffracted light periodically increases and decreases with the separation of the double-slit.