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The primary function of the sensory cortex is to discriminate sensation: appreciation and recognition of spatial relations, appreciation of similarity and differences of external objects, precise localization of the point touched, and identification of objects (stereognosis). Although less carefully examined than motor or speech abnormalities, somatosensory abnormality is present in at least half of stroke patients. The sensory abnormality is characterized by the presence of paresthesias and a selective loss of lemniscal sensation. Pontine tegmental strokes affecting the sensory tracts are often accompanied by sensory symptoms. Concomitant involvement of the adjacent pyramidal tract results in a sensory-motor stroke, and additional involvement of the cerebellothalamic fibers at the ventrolateral nucleus may produce a hypesthetic ataxic hemiparesis syndrome. Although motor symptoms are usually dominant in patients with subcortical strokes, small or even relatively large lesions primarily affecting the thalamocortical sensory radiation can result in pure or predominant sensory symptoms.
This chapter focuses on the most frequent vertigo syndromes. Characteristic symptoms of Benign paroxysmal positioning vertigo (BPPV) include brief, in part, severe attacks of rotatory vertigo with and without nausea, which are caused by rapid changes in head If the typical positioning nystagmus can be elicited without any additional central signs and symptoms. Menière's disease is typically a combination of abruptly occurring attacks with vestibular and/or cochlear symptoms, fluctuating, slowly progressive hearing loss and, in the course of time, tinnitus. Vertigo and nausea are reduced by antivertiginous drugs used in other acute disorders of labyrinthine function, for example, dimenhydrinate 100 mg as suppository or benzodiazepine. The differential diagnosis of perilymph fistulas includes the following illnesses: BPPV, positional vertigo of central origin, Menière's disease, vestibular paroxysmia, somatoform phobic postural vertigo, labyrinthine trauma and bilateral vestibulopathy. Differentiating vestibular migraine from transient ischemic attacks, Menière's disease or vestibular paroxysmia can occasionally be difficult.
Vertigo is an unpleasant distortion of static gravitational orientation or an erroneous perception of motion of either the sufferer or the environment. It is not a well-defined disease entity, but rather the outcome of many pathological processes causing a mismatch between the visual, vestibular, and somatosensory systems, all of which subserve both static and dynamic spatial orientation. Physiological and clinical vestibular vertigo syndromes are commonly characterized by a combination of phenomena involving perceptual, ocular motor, postural and vegetative manifestations: vertigo, nystagmus, ataxia and nausea (Brandt & Daroff, 1980). The vertigo itself results from a disturbance of cortical spatial orientation, while nystagmus and ocular deviations are secondary to a direction-specific imbalance in the vestibulo-ocular reflex. Postural imbalance and vestibular ataxia are caused by inappropriate or abnormal inactivation of vestibulospinal pathways. Unpleasant vegetative effects, such as nausea and vomiting, are related to clinical activation of the medullary vomiting centre (Brandt, 1991b).
Most of the central vestibular syndromes and some of the peripheral vestibular syndromes may have a vascular etiology (Baloh, 1992; Brandt & Dieterich, 1994a). Ischemia can be responsible for a wide range of vestibular syndromes; most of the central and some of the peripheral vestibular syndromes are listed in Table 10.1. Ischemia will sometimes produce a combination of central and peripheral symptoms, as in anterior inferior cerebellar artery (AICA) infarctions, the territory of which encompasses the labyrinth, pontine, and cerebellar structures (Atkinson, 1949). In migraine and in vertebrobasilar ischemia, it may not be possible to determine whether the vertigo is a symptom of a peripheral or a central vestibular syndrome. The course and prognosis of the vertigo syndrome are variable.
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