The cerebral cortex contains 2 types of neurons: principal (mostly pyramidal) neurons, which constitute approximately 80% of the total population, and local interneurons, which constitute approximately 20% of the total population, with some species variation. Pyramidal cells are excitatory glutamatergic neurons that participate in cortico-cortical connections or project to subcortical areas. Local interneurons utilize γ-aminobutyric acid (GABA) as their primary neurotransmitter and participate in local circuits in the cerebral cortex. Normal sensory perception, attention, and planning and execution of behaviors depend on interactions among canonical neocortical circuits involving excitatory and inhibitory neurons. Cortical interneurons have a fundamental role in shaping cortical circuits and controlling neocortical network interactions. These interneurons form functionally distinct networks that are temporally coordinated by electrical coupling via gap junctions, and establish GABAergic synapses not only with pyramidal neurons but also among each other. Via these interactions, GABAergic interneurons control the timing of pyramidal cell firing, generation of cortical rhythms, organization of sensory fields, and cortical plasticity. Impaired activity of neocortical inhibitory interneurons has been associated with several neurologic and psychiatric disorders, including epilepsy, mental retardation, schizophrenia, and autism. There are many comprehensive reviews on GABAergic interneuron heterogeneity, development, plasticity, function in shaping cortical activity, and involvement in disease.
Neurology July 16, 2013 vol. 81 no. 3 273-280
martedì 16 luglio 2013
Development and validation of a clinical guideline for diagnosing blepharospasm.
Neurology. 2013 Jun 14. [Epub ahead of print]
Abstract
OBJECTIVE:
To design and validate a clinical diagnostic guideline for aiding physicians in confirming or refuting suspected blepharospasm.
METHODS:
The guideline was developed and validated in a 3-step procedure: 1) identification of clinical items related to the phenomenology of blepharospasm, 2) assessment of the relevance of each item to the diagnosis of blepharospasm, and 3) evaluation of the reliability and diagnostic sensitivity/specificity of the selected clinical items.
RESULTS:
Of 19 clinical items initially identified, 7 were admitted by content validity analysis to further assessment. Both neurologists and ophthalmologists achieved satisfactory interobserver agreement for all 7 items, including "involuntary eyelid narrowing/closure due to orbicularis oculi spasms," "bilateral spasms," "synchronous spasms," "stereotyped spasm pattern," "sensory trick," "inability to voluntarily suppress the spasms," and "blink count at rest." Each selected item yielded unsatisfactory accuracy in discriminating patients with blepharospasm from healthy subjects and patients with other eyelid disturbances. Combining the selected items, however, improved diagnostic sensitivity/specificity. The best combination, yielding 93% sensitivity and 90% specificity, was an algorithm starting with the item "stereotyped, bilateral, and synchronous orbicularis oculi spasms inducing eyelid narrowing/closure" and followed by recognition of "sensory trick" or, alternatively, "increased blinking." CONCLUSION: This study provides an accurate and valid clinical guideline for diagnosing blepharospasm. Use of this guideline would make it easier for providers to recognize dystonia in clinical and research settings
domenica 14 luglio 2013
sabato 13 luglio 2013
Discovering strange diseases: Cerebral–Renal Salt Wasting
Cerebral or the preferred term, renal salt wasting (RSW), remains an unresolved syndrome that has historically evolved from being considered nonexistent to acceptance as a distinct clinical syndrome. Yet, differences over its prevalence continue. Many with RSW are diagnosed and treated for SIADH, which has diametrically opposite therapeutic goals from RSW, that is, to water-restrict in SIADH and administer salt and water in RSW. The major obstacles to differentiating SIADH from RSW are the overlapping of significant findings and clinical associations of both syndromes and our inability to assess the volume status of these patients, being volume-depleted in RSW and expanded in SIADH. In this chapter, we (1) redefine RSW, (2) review the pathophysiology of RSW, (3) review relevant volume studies, which prove RSW to be much more common than SIADH in neurosurgical patients, (4) review the complexities of differentiating RSW from SIADH, focusing on how a previously increased FEurate normalizes in SIADH as compared to being persistently increased in RSW after correction of hyponatremia, (5) review the emerging importance of determining fractional excretion (FE) of urate, which surpasses serum urate in the evaluation of hyponatremic conditions, (6) increased FEurate in the presence of normonatremia is suggestive of RSW, (7, 8) A normal FEurate in nonedematous hyponatremia is highly suggestive of reset osmostat, (9) present an algorithm that uses FEurate as central to the evaluation of the hyponatremic patient, (10). demonstrate the presence of a natriuretic factor in RSW that has different characteristics from A/BNP (11) advocate changing cerebral salt wasting to RSW based on reports of RSW occurring in patients without clinical cerebral disease and eliminating reset osmostat as a subtype of SIADH based on a normal FEurate and the predictability of ADH response to changes in serum osmolality, and (12) awareness, that symptoms with potentially serious complications are associated with hyponatremia, creates a therapeutic urgency to improve methods of differentiating RSW from SIADH.
Hyponatremia 2013, pp 65-85
Brain network connectivity assessed using graph theory in frontotemporal dementia
- Federica Agosta, MD, PhD,
- Sara Sala, PhD,
- Paola Valsasina, MSc,
- Alessandro Meani, MSc,
- Elisa Canu, MSc,
- Giuseppe Magnani, MD,
- Stefano F. Cappa, MD,
- Elisa Scola, MD,
- Piero Quatto, PhD,
- Mark A. Horsfield, PhD,
- Andrea Falini, MD,
- Giancarlo Comi, MD and
- Massimo Filippi, MD
ABSTRACT
Objective: To investigate whether brain functional network connectivity is disrupted in patients with the behavioral variant of frontotemporal dementia (bvFTD).
Methods: Graph theoretical analysis was applied to resting state functional MRI data from 18 patients with probable bvFTD and 50 healthy individuals. Functional connectivity between 90 cortical and subcortical brain regions was estimated using bivariate correlation analysis and thresholded to construct a set of undirected graphs. Correlations between network properties and cognitive variables were tested.
Results: Global topologic organization of the functional brain network in bvFTD was significantly disrupted as indicated by reduced mean network degree, clustering coefficient, and global efficiency and increased characteristic path length and assortativity relative to normal subjects. Compared to controls, bvFTD data showed retention of major “hub” regions in the medial parietal, temporal, and occipital lobes, but cortical hubs were not noted in the frontal lobes. Medial and dorsal frontal regions, left caudate nucleus, left insular cortices, and some regions of the temporal, parietal, and occipital lobes showed decreased nodal centrality. BvFTD patients showed the greatest decrease in inter-regional connectivity between the frontal and occipital regions, and the insular cortices and occipital, temporal, subcortical, and frontal regions. In bvFTD, altered global network properties correlated with executive dysfunction.
Conclusions: Global and local functional networks are altered in bvFTD, suggesting a loss of efficiency in information exchange between both distant and close brain areas. Altered brain regions are located in structures that are closely associated with neuropathologic changes in bvFTD. Aberrant topology of the functional brain networks in bvFTD appears to underlie cognitive deficits in these patients.
Neurology July 9, 2013 vol. 81 no. 2 134-143
giovedì 11 luglio 2013
Cerebral hyperperfusion syndrome
Cerebral hyperperfusion syndrome: a novel presentation of internal carotid artery dissection
Cervical artery dissection (CeAD) occurs preferentially in the middle-aged, and its annual incidence rate is 2.6 to 3.0 per 100,000. Manifestations of internal carotid artery dissection (ICAD) include ischemic stroke and TIA (>70% of patients), headache, neck pain, Horner syndrome, cranial nerve palsy, pulsatile tinnitus, and, rarely, subarachnoid hemorrhage. Cerebral hyperperfusion syndrome is known to occur after carotid artery revascularization procedures and it is thought to result from the combination of several factors that impair cerebral vascular autoregulatory mechanisms.
Neurology, July 3 2013
Iscriviti a:
Post (Atom)