Hearing Loss & Dizziness Flashcards
Δοκιμασίες Rinne και Weber
Δοκιμασία Rinne: Συγκρίνουμε την ακοή της αέρινης με την οστέινη οδό. Φυσιολογικός χρόνος αντίληψης των δονήσεων μέσω της μαστοειδούς είναι το 1/3 του χρόνου αντίληψης με την αέρινη οδό. Βάζουμε το διαπασών στη μαστοειδή απόφυση και όταν πάψει να γίνεται αντιληπτό το μεταφέρουμε μπροστά στο αυτί. Αν ο ήχος συνεχίζει να ακούγεται λέμε ότι το Rinne είναι θετικό (αλλιώς αρνητικό).
Δοκιμασία Weber: Βάζουμε το δονούμενο διαπασών στο μέτωπο. Φυσιολογικά ο ήχος δεν πλαγιώνει αλλά ακούγεται εξίσου και στα δύο αυτιά.
Εντοπιστική διαγνωστική σε διαταραχές λειτουργίας του κοχλιακού
Βαρηκοΐα τύπου αγωγιμότητας: βλάβη μέσου ωτός ή απόφραξη έξω ακουστικού πόρου. Η ακοή με την αέρινη οδό είναι μειωμένη ενώ με την οστέινη οδό είναι φυσιολογική.
Στη δοκιμασία Weber ο ήχος ακούγεται καλύτερα στο αυτί που πάσχει γιατί το έσω ους στο αυτί αυτό είναι απομονωμένο από εξωτερικούς ήχους.
Δοκιμασία rinne αρνητική.
Νευροαισθητηριακή βαρηκοΐα: βλάβη του έσω ωτός ή του ακουστικού νεύρου.
Ακοή καταργημένη τόσο με την αέρινη όσο και με την οστέινη οδό.
Δοκιμασία rinne θετική.
Στη δοκιμασία Weber ο ήχος πλαγιώνει στο γερό αυτί.
Υπερπυρηνικές βλάβες: πρέπει να είναι αμφοτερόπλευρες για να προκαλέσουν βαρηκοΐα. Ετερόπλευρες βλάβες γίνονται αντιληπτές με την εξέταση ακουστικών προκλητών δυναμικών.
Pulsatile tinnitus causes
- Vascular (most common) (eg dural arteriovenous fistula [AVF] or a carotid-cavernous sinus fistula)
- Idiopathic endocranial hypertension
- Muscular (spasm of one or both of the muscles within the middle ear (the tensor tympani and the stapedius muscle) or palatal myoclonus
- Paraganglioma
Characteristics of spontaneous peripheral nystagmus
1) unidirectional (the eyes beat only to one side)
2) peripheral spontaneous nystagmus never changes direction
3) usually a horizontal greater than torsional pattern
4) suppression with visual fixation
5) increase in velocity with gaze in direction of fast phase and decrease with direction opposite of the fast phase
What are saccadic intrusions? Which are the most common types and where are they seen?
Saccadic intrusions are spontaneous, involuntary saccadic movements of the eyes, without the rhythmic fast and slow phases characteristic of nystagmus.
Most common types:
1) square-wave jerks (small amplitude involuntary saccades that take eyes off a target, followed after a normal intersaccadic delay (around 200 ms) by a corrective saccade to bring the eyes back to target. Found in cerebellar ataxia, Huntington disease, psp, normal individuals
2) saccadic oscillations (back-to-back saccadic movements without the intersaccadic interval characteristic of square wave jerks so their appearance is that of an oscillation)
Conditions causing impaired smooth pursuit
1) Disorders throughout CNS
2) Tranquilizing medicines
3) alcohol
4) inadequate concentration or vision
5) fatigue
++ In a cognitively intact individual presenting with dizziness or imbalance symptoms, bilaterally impaired smooth pursuit is highly localising to the cerebellum
Perpheral vestibular system anatomy
The peripheral vestibular system is composed of three
semicircular canals, the utricle and saccule, and the vestibular component of the eighth cranial nerve
Each semicircular canal has a sensory epithelium called the crista; the sensory epithelium of the utricle and saccule is called the macule.
Peripheral vestibular systmen function
The semicircular canals sense angular movements, and the utricle and saccule sense linear movements.
Two of the semicircular canals (anterior and posterior) are oriented in the vertical plane nearly orthogonal to each other; the third canal is oriented in the horizontal plane (horizontal canal). The crista of each canal is activated by movement occurring in the plane of that canal. When the hair cells of these organs are stimulated, the signal is transferred to the vestibular nuclei via the vestibular portion of cranial nerve VIII. Signals originating from the horizontal semicircular canal then pass via the medial longitudinal fasciculus along the floor of the fourth ventricle to the abducens nuclei in the middle brainstem and the ocular motor complex in the rostral brainstem.
The anterior and posterior canal impulses pass from the vestibular nuclei to the ocular motor nucleus and trochlear nucleus, triggering eye movements roughly in the plane of each canal.
*A key feature is that once vestibular signals leave the vestibular nuclei they divide into vertical, horizontal, and torsional components. As a result, a lesion of central vestibular pathways can cause a pure vertical, pure torsional, or pure horizontal nystagmus
Explain eye movements in respect to vestibular afferent signals
The primary vestibular afferent nerve fibers maintain a
constant baseline firing rate of action potentials.
When the baseline rate from each ear is symmetrical (or an asymmetry has been centrally compensated), the eyes remain stationary.
With an uncompensated asymmetry in the firing rate, resulting from either increased or decreased activity on one side, slow ocular deviation results.
By turning the head to the right, the baseline firing rate of the horizontal canal is physiologically altered, causing an increased firing rate on the right side and a decreased firing rate on the left side. The result is a slow deviation of the eyes to the left. In an alert subject, this slow deviation is regularly interrupted by quick movements in the opposite direction (nystagmus), so the eyes do not become pinned to one side. In a comatose patient, only the slow component is seen because the brain cannot generate the corrective fast components (doll’s eyes)
What is static and dynamic equilibrium
The sense organs located in the utricle and saccule function in static equilibrium, a function needed to sense the position of the head relative to gravity or to sense acceleration or deceleration of the body
The sense organs associated with the semicircular ducts function in dynamic equilibrium, a function needded to maintain balance when the head or body itself is rotated or suddenly moved
Head- thrust test
How to perform and what do the findings mean
The patient sits in front of the examiner and the examiner holds the patients head steady in the midline. The patient is instructed to maintain gaze on the nose of the examiner. The examiner then quickly turns the patients head about 10-15 degrees to one side and observes the ability of the patient to keep the eyes locked in the examiners nose.
A) If the patient’s eyes stay locked on the examiners nose then the peripheral vestibular system is assumed to be intact. Thus when a patient presents with the acute vestibular syndrome the test would suggest a CNS lesion
B) If the patient’s eyes move with the head and then the patient makes a corrective saccade then this indicates a lesion of the peripheral vestibular system
HINTS test sensitivity/specificity
100% sensitive
96% specific
More sensitive than MRI in detecting stroke within 48h of an acute vestibuar syndrome!
Abnormal ocular motor findings in patients with brainstem or cerebellar strokes
1) spontaneous nystagmus purely vertical or torsional
2) direction-changing gaze evoked nystagmus
3) impairment of smooth pursuit
4) overshooting saccades
Red flags for central vestibular lesion (e.g. stroke)
1) other central signs or symptoms
2) direction-changing nystagmus
3) vertical nystagmus
4) negative head-thrust test (no corrective saccade after the head thrust test to the direction opposite the fast phase of spontaneous nystagmus)
5) skew deviation
6) substantial stroke risk factors
BPPV diagnosis
In patients with typical symptoms, perform a provoking maneuver and observe symptoms and nystagmus to confirm the diagnosis of BPPV and localize the abnormality.
●The Dix-Hallpike maneuver is used to identify posterior canal BPPV, the most common subtype.
The Dix-Hallpike maneuver will usually provoke paroxysmal vertigo and nystagmus when the affected ear is turned downward during the maneuver
●If the Dix-Hallpike maneuver does not identify posterior canal BPPV, evaluate for other subtypes with an appropriate maneuver and consider alternative diagnoses.
Distinguishing among common peripheral and central vertigo syndromes
