Vijay Kannan

Neural substrates of visuospatial processing in distinct reference frames: Evidence from unilateral spatial neglect

There is evidence for different levels of visuospatial processing with their own frames of reference: viewer-centered, stimulus-centered, and object-centered. The neural locus of these levels can be explored by examining lesion location in subjects with unilateral spatial neglect (USN) manifest in these reference frames. Most studies regarding the neural locus of USN have treated it as a homogenous syndrome, resulting in conflicting results. In order to further explore the neural locus of visuospatial processes differentiated by frame of reference, we presented a battery of tests to 171 subjects within 48 hr after right supratentorial ischemic stroke before possible structural and/or functional reorganization. The battery included MR perfusion weighted imaging (which shows hypoperfused regions that may be dysfunctional), diffusion weighted imaging (which reveals areas of infarct or dense ischemia shortly after stroke onset), and tests designed to disambiguate between various types of neglect. Results were consistent with a dorsal/ventral stream distinction in egocentric/allocentric processing. We provide evidence that portions of the dorsal stream of visual processing, including the right supramarginal gyrus, are involved in spatial encoding in egocentric coordinates, whereas parts of the ventral stream (including the posterior inferior temporal gyrus) are involved in allocentric encoding.

Unilateral neglect is more severe and common in older patients with right hemispheric stroke

Introduction: Unilateral neglect after acute right hemispheric stroke significantly impedes poststroke recovery. We studied patients with right hemispheric stroke to determine whether increasing age was associated with more frequent or more severe neglect. Methods: Eight neglect tests within 5 days of symptom onset (and within 24 hours of admission) were administered to 204 subjects with acute right hemispheric stroke. Size of infarct was measured, and neglect tests were scored as percent error. “Any neglect” was defined by an elevated neglect test score, standardized relative to a group of normal controls. Results: When tested for neglect soon after acute stroke admission, 69.6% of subjects older than 65 years had “any neglect” (defined by comparison to a group of normal controls), compared with 49.4% of subjects aged 65 years and younger (p = 0.008). For every additional 10 years of age, patients were 1.83 times as likely to have neglect, even after adjusting for diffusion-weighted imaging (DWI) infarct volume and NIH Stroke Scale (NIHSS) score (95% CI 1.38–2.43). In addition, DWI volume and NIHSS independently predicted neglect. Score on virtually all of the neglect tests worsened as an effect of age. Percentage error on a line cancellation task was 3.8% higher for every additional 10 years of age, after adjustment for DWI volume and NIHSS (p = 0.006). Similar results were found for other neglect tests. Conclusions: Increasing age in patients with acute right hemispheric stroke significantly increases the odds of unilateral neglect as well as severity of neglect, independently of size of the stroke or NIH Stroke Scale score. The reason for this finding in older patients may be because they have more brain atrophy and may be less able to compensate for cerebral infarction, or because they tend to have more cardioembolic strokes, which may be more cortically based.

Where (in the brain) do semantic errors come from

BACKGROUND Semantic errors result from the disruption of access either to semantics or to lexical representations. One way to determine the origins of these errors is to evaluate comprehension of words that elicit semantic errors in naming. We hypothesized that in acute stroke there are different brain regions where dysfunction results in semantic errors in both naming and comprehension versus those with semantic errors in oral naming alone. METHODS A consecutive series of 196 patients with acute left hemispheric stroke who met inclusion criteria were evaluated with oral naming and spoken word/picture verification tasks and magnetic resonance imaging within 48 h of stroke onset. We evaluated the relationship between tissue dysfunction in 10 pre-specified Brodmanns areas (BA) and the production of coordinate semantic errors resulting from (1) semantic deficits or (2) lexical access deficits. RESULTS Semantic errors arising from semantic deficits were most associated with tissue dysfunction/infarct of left BA 22. Semantic errors resulting from lexical access deficits were associated with hypoperfusion/infarct of left BA 37. CONCLUSION Our study shows that semantic errors arising from damage to distinct cognitive processes reflect dysfunction of different brain regions.

Therapy for naming deficits in two variants of primary progressive aphasia

Background: Primary progressive aphasia (PPA) refers to a progressive and selective decline in language due to neurodegenerative disease. There are three variants of PPA, progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopaenic progressive aphasia (LPA). All variants include impaired object naming, but distinct underlying deficits might interfere with naming. Therefore, individuals with different types of PPA may respond differently to naming therapy. Aims: To identify differences in patterns of success and generalisation in response to the same treatment in patient with LPA and a patient with SD. Furthermore, we wished to identify whether the treatment effect was item specific (trained words) or generalised to untrained words in trained or untrained categories. Methods & Procedures: Participants included an individual with LPA and one with SD. An assessment of lexical processing was administered before and after a naming treatment to assess underlying deficits and generalisation effects. Therapy consisted of a cueing hierarchy treatment. Treatment items consisted of pictured objects in the categories of fruits/vegetables and clothing. Outcomes & Results: Two different patterns of performance were observed. The LPA participant improved in naming of treated items and untreated items in both treated and untreated categories. The participant with SD improved in naming treated items only, but showed less deterioration in untreated items in treated than untreated categories. Conclusions: Individuals with PPA can show improved naming (at least temporarily) with therapy, but generalisation to untrained items may depend on the underlying cause of the naming deficit, which may differ across subtypes.

Site of the ischemic penumbra as a predictor of potential for recovery of functions

Background and Purpose: Diffusion–perfusion mismatch has been used to estimate salvageable tissue and predict potential for recovery in acute stroke. Location of the salvageable tissue may be as important as volume or percentage in predicting potential for recovery of specific functions. Impaired naming, a common and disabling deficit after left hemisphere stroke, is often associated with tissue dysfunction of left Brodmann area (BA) 37, posterior inferior temporal cortex. We tested the hypothesis that the presence of diffusion–perfusion mismatch within left BA 37 predicts probability and extent of short-term improvement of naming. Methods: One hundred five patients with acute left hemisphere ischemic stroke had diffusion-weighted imaging, perfusion-weighted imaging, a test of picture naming, and other language tests at admission and 2 to 4 days later. Linear regression was used to determine whether diffusion–perfusion mismatch in any BA in language cortex, total volume of mismatch, or diffusion or perfusion abnormality predicted degree of improvement in naming by days 3 to 5. Results: The presence of >20% diffusion–perfusion mismatch in left BA 37 and total volumes of diffusion and perfusion abnormality at day 1 each independently predicted degree of improvement in naming. Mismatch in this area did not predict the degree of improvement in other language tests or the NIH Stroke Scale in this study. Conclusions/Relevance: Diffusion–perfusion mismatch in left Brodmann area 37 was strongly associated with acute improvement in naming, independently of volume or percentage of total mismatch or diffusion or perfusion abnormality. These data indicate that mismatch in a particular area is a marker of salvageable tissue and an important predictor of potential for recovery of functions that depend on that area. Location of mismatch before treatment may help to predict potential benefits of reperfusion. GLOSSARY: ADC = apparent diffusion coefficient; BA = Brodmann area; DWI = diffusion-weighted imaging; NIHSS = NIH Stroke Scale; PWI = perfusion-weighted imaging; TE = echo time; TR = repetition time; TTP = time to peak.

The Contribution of Neuroimaging to the Study of Language and Aphasia

New structural and functional imaging methods continue to be developed at a rapid pace. In the last 25 years, advanced imaging techniques have provided insights into how language is represented and processed in the brain and how it can be disrupted by damage to, or dysfunction of, various parts of the brain. Imaging studies have also yielded new information regarding how individuals recover language after stroke. We briefly review the strengths and weaknesses of the various radiological methods currently used to study language and aphasia.

The Burden of Acute Disease in Mahajanga, Madagascar – A 21 Month Study

Background Efforts to develop effective and regionally-appropriate emergency care systems in sub-Saharan Africa are hindered by a lack of data on both the burden of disease in the region and on the state of existing care delivery mechanisms. This study describes the burden of acute disease presenting to an emergency unit in Mahajanga, Madagascar. Methods and Findings Handwritten patient registries on all emergency department patients presenting between 1 January 2011 and 30 September 2012 were reviewed and data entered into a database. Data included age, sex, diagnosis, and disposition. We classified diagnoses into Clinical Classifications Software (CCS) multi-level categories. The population was 53.5% male, with a median age of 31 years. The five most common presenting conditions were 1) Superficial injury; contusion, 2) Open wounds of head; neck; and trunk, 3) Open wounds of extremities, 4) Intracranial injury, and 5) Unspecified injury and poisoning. Trauma accounted for 48%, Infectious Disease for 15%, Mental Health 6.1%, Noncommunicable 29%, and Neoplasms 1.2%. The acuity seen was high, with an admission rate of 43%. Trauma was the most common reason for admission, representing 19% of admitted patients. Conclusions This study describes the burden of acute disease at a large referral center in northern Madagascar. The Centre Hôpitalier Universitaire de Mahajanga sees a high volume of acutely ill and injured patients. Similar to other reports from the region, trauma is the most common pathology observed, though infectious disease was responsible for the majority of adult mortality. Typhoid fever other intestinal infections were the most lethal CCS-coded pathologies. By utilizing a widely understood classification system, we are able to highlight contrasts between Mahajanga’s acute and overall disease burden as well as make comparisons between this region and the rest of the globe. We hope this study will serve to guide the development of context-appropriate emergency medicine systems in the region.

Patterns of reading performance in acute stroke: A descriptive analysis

One of the main sources of information regarding the underlying processes involved in both normal and impaired reading has been the study of reading deficits that occur as a result of brain damage. However, patterns of reading deficits found acutely after brain injury have been little explored. The observed patterns of performance in chronic stroke patients might reflect reorganization of the cognitive processes underlying reading or development of compensatory strategies that are not normally used to read. Method: 112 acute left hemisphere stroke patients were administered a task of oral reading of words and pseudowords within 1–2 days of hospital admission; performance was examined for error rate and type, and compared to that on tasks involving visual lexical decision, visual/auditory comprehension, and naming. Results: Several distinct patterns of performance were identified. Although similarities were found between the patterns of reading performance observed acutely and the classical acquired dyslexias generally identified more chronically, some notable differences were observed. Of interest was the finding that no patient produced any pure semantic errors in reading, despite finding such errors in comprehension and naming.

Geolocalization of Influenza Outbreak Within an Acute Care Population: A Layered-Surveillance Approach

STUDY OBJECTIVE We seek to use a novel layered-surveillance approach to localize influenza clusters within an acute care population. The first layer of this system is a syndromic surveillance screen to guide rapid polymerase chain reaction testing. The second layer is geolocalization and cluster analysis of these patients. We posit that any identified clusters could represent at-risk populations who could serve as high-yield targets for preventive medical interventions. METHODS This was a prospective observational surveillance study. Patients were screened with a previously derived clinical decision guideline that has a 90% sensitivity and 30% specificity for influenza. Patients received points for the following signs and symptoms within the past 7 days: cough (2 points), headache (1 point), subjective fever (1 point), and documented fever at triage (temperature >38°C [100.4°F]) (1 point). Patients scoring 3 points or higher were indicated for influenza testing. Patients were tested with Xpert Flu (Cepheid, Sunnyvale, CA), a rapid polymerase chain reaction test. Positive results were mapped with ArcGIS (ESRI, Redlands, CA) and analyzed with kernel density estimation to create heat maps. RESULTS There were 1,360 patients tested with Xpert Flu with retrievable addresses within the greater Phoenix metro area. One hundred sixty-seven (12%) of them tested positive for influenza A and 23 (2%) tested positive for influenza B. The influenza A virus exhibited a clear cluster pattern within this patient population. The densest cluster was located in an approximately 1-square-mile region southeast of our hospital. CONCLUSION Our layered-surveillance approach was effective in localizing a cluster of influenza A outbreak. This region may house a high-yield target population for public health intervention. Further collaborative efforts will be made between our hospital and the Maricopa County Department of Public Health to perform a series of community vaccination events before the next influenza season. We hope these efforts will ultimately serve to reduce the burden of this disease on our patient population, and that this system will serve as a framework for future investigations locating at-risk populations.

The clinical practice of emergency medicine in Mahajanga, Madagascar

Introduction Little is documented concerning the clinical practice of emergency care in low- and middle-income countries. The lack of structural models presents serious obstacles to the development of effective emergency care services. This study provides such a model by describing the clinical practice at the emergency centre of the Centre Hôpitalier Universitaire de Mahajanga in Madagascar. Methods This was a retrospective chart review of all adult patients presenting to the emergency centre from September to November 2012. Archived chart data were extracted into a computer database. Data included: age, sex, date, diagnostic investigations, procedures, medications, and diagnosis. Results 727 charts were reviewed, averaging eight patients per day. The three most frequent pathologies observed were trauma, gastrointestinal, and infectious disease. A total of 392 received diagnostic investigations. These were chiefly complete blood counts (n = 218), blood glucose (n = 155) and ECG (n = 92). Chest X-rays (n = 83), extremity X-rays (n = 55) and skull/face X-rays (n = 44) comprised the most common imaging. Ultrasounds were primarily abdominal (n = 9), renal/genitourinary (n = 6), and obstetric (n = 2). Therapeutic interventions were performed in 564 patients, most commonly intravenous access (n = 452) and wound/orthopaedic care (n = 185). Medications were administered to 568 patients, mostly anti-inflammatory/analgesics (n = 463) and antibiotics (n = 287). Conclusion This is the first descriptive study of the clinical practice of emergency medicine in Mahajanga, Madagascar. It provides both the Malagasy and international medical communities with an objective analysis of the practice of emergency care in Madagascar from both diagnostic and therapeutic standpoints. Emergency care here focuses on the management of traumatic injury and infectious disease. The diagnostic imaging, pharmacologic and procedural therapeutic interventions reflect the burdens placed upon this institution by these diseases. We hope this study will provide guidance for the further development of Malagasy-specific emergency care systems.