Chapter 022. Dizziness and Vertigo (Part 1)

Harrisons Internal Medicine Chapter 22. Dizziness and VertigoDizziness and Vertigo: IntroductionDizziness is a common and often vexing symptom. Patients use the term to encompass a variety of sensations, including those that seem semantically appropriate (e.g., lightheadedness, faintness, spinning, giddiness) and those that are misleadingly inappropriate, such as mental confusion, blurred vision, headache, or tingling.Moreover, some individuals with gait disorders caused by peripheral neuropathy, myelopathy, spasticity, parkinsonism, or cerebellar ataxia complain of "dizziness" despite the absence of vertigo or other abnormal cephalic sensations. In this context, the term dizziness is being used to describe disturbed ambulation. ...
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Chapter 022. Dizziness and Vertigo (Part 1) Chapter 022. Dizziness and Vertigo (Part 1) Harrisons Internal Medicine > Chapter 22. Dizziness and Vertigo Dizziness and Vertigo: Introduction Dizziness is a common and often vexing symptom. Patients use the term toencompass a variety of sensations, including those that seem semanticallyappropriate (e.g., lightheadedness, faintness, spinning, giddiness) and those thatare misleadingly inappropriate, such as mental confusion, blurred vision,headache, or tingling. Moreover, some individuals with gait disorders caused by peripheralneuropathy, myelopathy, spasticity, parkinsonism, or cerebellar ataxia complain ofdizziness despite the absence of vertigo or other abnormal cephalic sensations.In this context, the term dizziness is being used to describe disturbed ambulation. There may be mild associated lightheadedness, particularly with impairedsensation from the feet or poor vision; this is known as multiple-sensory-defectdizziness and occurs in elderly individuals who complain of dizziness only whenwalking. Decreased position sense (secondary to neuropathy or myelopathy) andpoor vision (from cataracts or retinal degeneration) create an overreliance on theaging vestibular apparatus. A less precise but sometimes comforting designation to patients is benigndysequilibrium of aging. Thus, a careful history is necessary to determine exactlywhat a patient who states, Doctor, Im dizzy, is experiencing. After eliminating the misleading symptoms or gait disturbance, dizzinessusually means either faintness (presyncope) or vertigo (an illusory or hallucinatorysense of movement of the body or environment, most often a feeling of spinning).Operationally, after obtaining the history, dizziness may be classified into threecategories: (1) faintness, (2) vertigo, and (3) miscellaneous head sensations. Faintness Prior to an actual faint (syncope), there are often prodromal presyncopalsymptoms (faintness) reflecting ischemia to a degree insufficient to impairconsciousness. These include lightheadedness, dizziness without true vertigo, afeeling of warmth, diaphoresis, nausea, and visual blurring occasionallyproceeding to blindness. Presyncopal symptoms vary in duration and may increase in severity untilloss of consciousness occurs or may resolve prior to loss of consciousness if thecerebral ischemia is corrected. Faintness and syncope are discussed in detail inChap. 21. Vertigo Vertigo is usually due to a disturbance in the vestibular system. The endorgans of this system, situated in the bony labyrinths of the inner ears, consist ofthe three semicircular canals and the otolithic apparatus (utricle and saccule) oneach side. The canals transduce angular acceleration, while the otoliths transducelinear acceleration and the static gravitational forces that provide a sense of headposition in space. The neural output of the end organs is conveyed to the vestibular nuclei inthe brainstem via the eighth cranial nerves. The principal projections from thevestibular nuclei are to the nuclei of cranial nerves III, IV, and VI; spinal cord;cerebral cortex; and cerebellum. The vestibuloocular reflex (VOR) serves to maintain visual stability duringhead movement and depends on direct projections from the vestibular nuclei to thesixth cranial nerve (abducens) nuclei in the pons and, via the medial longitudinalfasciculus, to the third (oculomotor) and fourth (trochlear) cranial nerve nuclei inthe midbrain. These connections account for the nystagmus (to-and-fro oscillation of theeyes) that is an almost invariable accompaniment of vestibular dysfunction. Thevestibular nerves and nuclei project to areas of the cerebellum (primarily theflocculus and nodulus) that modulate the VOR. The vestibulospinal pathways assist in the maintenance of postural stability.Projections to the cerebral cortex, via the thalamus, provide conscious awarenessof head position and movement. The vestibular system is one of three sensory systems subserving spatialorientation and posture; the other two are the visual system (retina to occipitalcortex) and the somatosensory system that conveys peripheral information fromskin, joint, and muscle receptors. The three stabilizing systems overlap sufficiently to compensate (partiallyor completely) for each others deficiencies. Vertigo may represent eitherphysiologic stimulation or pathologic dysfunction in any of the three sensorysystems.