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Nervous System Dysfunction (Dizziness and Vertigo (DIFFERENTIAL DIAGNOSIS,…

- - - - neurologic
        
        eye movements
        
        range + whether they are equal in each eye; Peripheral eye movement disorders (e.g.,cranial neuropathies, eye muscle weakness) are usually disconjugate (different in the two eyes)
        
        pursuit (the ability to follow a smoothly moving target) + saccades (the ability to look back and forth accurately between two targets); Poor pursuit or inaccurate (dysmetric) saccades--> central pathology, often involving cerebellum.
        
        spontaneous nystagmus: most often of the jerk type: slow drift (slow phase) in one direction alternates with a rapid saccadic movement (quick phase or fast phase) in the opposite direction);
        
        if primary position nystagmus seen easily in the light:
        
        the rest: central cause; Two forms of nystagmus that are characteristic of lesions of cerebellar pathways
        
        vertical nystagmus with downward
        fast phases (downbeat nystagmus)
        
        horizontal nystagmus that changes direction with gaze (gaze-evoked nystagmus)
        
        peripheral exception: acute vestibulopathy (e.g., vestibular neuritis)
        
        seen with Frenzel eyeglasses: peripheral; peripheral lesions typically cause unidirectional horizontal nystagmus
        
        vestibular function
        
        The most useful bedside test of peripheral vestibular function: head impulse test (vestibuloocular reflex assessed with small-amplitude (~20 degrees) rapid head rotations; if deficient--> catch up saccade in opposite direction)
        
        bilateral hypofunction (catch-up saccades after rotations in both directions)
        
        unilateral hypofunction: (catch-up saccades after rotations toward the weak side)
        
        Dynamic visual acuity: Visual acuity is measured with the head still and when the head is rotated back and forth by the examiner (about 1–2 Hz). A drop in visual acuity during head motion of more than one line on a near card or Snellen chart is abnormal and indicates vestibular dysfunction
        
        hearing [the following was in ancillary testing]
        
        Audiometry should be performed whenever
        a vestibular disorder is suspected.
        
        Unilateral sensorineural hearing loss supports a peripheral disorder (e.g., vestibular schwannoma).
        
        Predominantly low-frequency hearing loss is characteristic of
        Ménière’s disease
        
        All patients with episodic dizziness, especially if provoked by
        positional change, should be tested with the Dix-Hallpike maneuver.
    - - Caloric testing assesses the responses of the two horizontal semicircular canals. The test battery often includes recording of saccades and pursuit to assess central ocular motor function
      - Neuroimaging is important if a central vestibular disorder is suspected. In addition, patients with unexplained unilateral hearing loss or vestibular hypofunction should undergo magnetic resonance imaging (MRI) of the internal auditory canals, including administration of gadolinium, to rule out a schwannoma.
      - Electronystagmography/videonystagmography: recordings of spontaneous nystagmus (if present) and measurement of positional nystagmus
    - - delineate more precisely nature of symptom; in case of vestibular disorders
        
        asymmetry of vestibular inputs from 2 labyrinths or
        in their central pathways--> Vertigo, an illusion of self or environmental motion, that is usually acute
        
        Symmetric bilateral vestibular hypofunction--> imbalance but no vertigo
      - patient symptoms generally unreliable; Hx should focus on other features (first attack? duration? prior episodes, provoking factors, and accompanying symptoms?)
      - Dizziness episodes
        
        brief (s): BPPV + orthostatic
        hypotension
        
        intermediate (m): vestibular migraine, Meniere's disease
        
        [prolonged} (hr): transient ischemic attacks of the posterior circulation; migraine; others
      - vertigo accompanying symptoms
        
        peripheral cause--> Unilateral hearing loss and other aural symptoms (ear pain, pressure, fullness) [bc auditory pathways quickly become bilateral upon entering brainstem, central lesions are unlikely to cause unilateral hearing loss, unless lesion lies near root entry zone of auditory nerve]
        
        central cause--> double vision (diplopia), numbness, dysarthria, limb ataxia