Sensory loss

Coma: a state of unconsciousness from which the patient cannot be aroused, even by powerful stimuli. Traumatic brain injuries are the most frequent cause; other causes include severe uncontrolled diabetes mellitus, liver disease, kidney disease, and neurologic conditions Dementia: a general loss of mental abilities, including impairment of memory and often impairments in speech, coordination, ability to understand sensory stimuli, and other mental faculties.

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Disorders of the Sense of Taste Disorders of the sense of taste are caused by conditions that interfere with the access of the tastant to the receptor cells in the taste bud (transport loss), injure receptor cells (sensory loss), or damage gustatory afferent nerves and central gustatory pathways (neural loss) (Table 30-2). Transport gustatory losses result from xerostomia due to many causes, including Sjögren's syndrome, radiation therapy, heavy-metal intoxication, and bacterial colonization of the taste pore.

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Disorders of the Sense of Smell These are caused by conditions that interfere with the access of the odorant to the olfactory neuroepithelium (transport loss), injure the receptor region (sensory loss), or damage central olfactory pathways (neural loss). Currently no clinical tests exist to differentiate these different types of olfactory losses. Fortunately, the history of the disease provides important clues to the cause.

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Harrison's Internal Medicine Chapter 27. Aphasia, Memory Loss, and Other Focal Cerebral Disorders Aphasia, Memory Loss, and Other Focal Cerebral Disorders: Introduction The cerebral cortex of the human brain contains ~20 billion neurons spread over an area of 2.5 m2. The primary sensory areas provide an obligatory portal for the entry of sensory information into cortical circuitry, whereas the primary motor areas provide final common pathways for coordinating complex motor acts. The primary sensory and motor areas constitute 10% of the cerebral cortex.

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Language allows the communication and elaboration of thoughts and experiences by linking them to arbitrary symbols known as words. The neural substrate of language is composed of a distributed network centered in the perisylvian region of the left hemisphere. The posterior pole of this network is located at the temporoparietal junction and includes a region known as Wernicke's area. An essential function of Wernicke's area is to transform sensory inputs into their lexical representations so that these can establish the distributed associations that give the word its meaning. ...

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Touch localization is performed by light pressure for an instant with the examiner's fingertip or a wisp of cottonwool; the patient, whose eyes are closed, is required to identify the site of touch with the fingertip. Bilateral simultaneous stimulation at analogous sites (e.g., the dorsum of both hands) can be carried out to determine whether the perception of touch is extinguished consistently on one side or the other. The phenomenon is referred to as extinction.

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Spinal Cord (See also Chap. 372) If the spinal cord is transected, all sensation is lost below the level of transection. Bladder and bowel function are also lost, as is motor function. Hemisection of the spinal cord produces the Brown-Séquard syndrome, with absent pain and temperature sensation contralaterally and loss of proprioceptive sensation and power ipsilaterally below the lesion (see Figs. 25-1 and 372-1). Numbness or paresthesias in both feet may arise from a spinal cord lesion; this is especially likely when the upper level of the sensory loss extends to the trunk.

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Anterior view of dermatomes (left) and cutaneous areas (right) supplied by individual peripheral nerves. (Modified from MB Carpenter and J Sutin, in Human Neuroanatomy, 8th ed, Baltimore, Williams & Wilkins, 1983.) Figure 25-3 Posterior view of dermatomes (left) and cutaneous areas (right) supplied by individual peripheral nerves. (Modified from MB Carpenter and J Sutin, in Human Neuroanatomy, 8th ed, Baltimore, Williams & Wilkins, 1983.)Temperature sensation, to both hot and cold, is best tested with small containers filled with water of the desired temperature.

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Examination of Sensation The main components of the sensory examination are tests of primary sensation (pain, touch, vibration, joint position, and thermal sensation; Table 251).

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Anatomy of Sensation Cutaneous afferent innervation is conveyed by a rich variety of receptors, both naked nerve endings (nociceptors and thermoreceptors) and encapsulated terminals (mechanoreceptors). Each type of receptor has its own set of sensitivities to specific stimuli, size and distinctness of receptive fields, and adaptational qualities. Much of the knowledge about these receptors has come from the development of techniques to study single intact nerve fibers intraneurally in awake, unanesthetized human subjects.

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Harrison's Internal Medicine Chapter 25. Numbness, Tingling, and Sensory Loss Numbness, Tingling, and Sensory Loss: Introduction Normal somatic sensation reflects a continuous monitoring process, little of which reaches consciousness under ordinary conditions. By contrast, disordered sensation, particularly when experienced as painful, is alarming and dominates the sufferer's attention. Physicians should be able to recognize abnormal sensations by how they are described, know their type and likely site of origin, and understand their implications. Pain is considered separately in Chap.

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Acute Monoparesis If the weakness is predominantly in distal and nonantigravity muscles and not associated with sensory impairment or pain, focal cortical ischemia is likely (Chap. 364); diagnostic possibilities are similar to those for acute hemiparesis. Sensory loss and pain usually accompany acute lower motor neuron weakness; the weakness is commonly localized to a single nerve root or peripheral nerve within the limb but occasionally reflects plexus involvement.

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Recurrent unilateral labyrinthine dysfunction, in association with signs and symptoms of cochlear disease (progressive hearing loss and tinnitus), is usually due to Ménière's disease (Chap. 30). When auditory manifestations are absent, the term vestibular neuronitis denotes recurrent monosymptomatic vertigo. Transient ischemic attacks of the posterior cerebral circulation (vertebrobasilar insufficiency) only infrequently cause recurrent vertigo without concomitant motor, sensory, visual, cranial nerve, or cerebellar signs (Chap. 364).

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Degenerative Conditions Lumbar spinal stenosis describes a narrowed lumbar spinal canal. Neurogenic claudication is the usual symptom, consisting of back and buttock or leg pain induced by walking or standing and relieved by sitting. Symptoms in the legs are usually bilateral. Lumbar stenosis, by itself, is frequently asymptomatic, and the correlation between the severity of symptoms and degree of stenosis of the spinal canal is poor. Unlike vascular claudication, symptoms are often provoked by standing without walking.

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