48

48 CASE 48


A 50-year-old man comes to the physician’s office complaining of a persistent and disabling sense that he is spinning even while he is sitting still.


The sensation has become progressively worse since it was first noted about 5 months ago. He has stopped social drinking but with no sign of improvement. He also indicates his left ear is problematic, with mild ear pain, a gradual decrease in hearing, and often a constant ringing (tinnitus).



PHYSICAL EXAMINATION



VS: T 37°C, P 72/min, R 15/min, BP 126/80 mm Hg

PE: The patient appears confused and has a mild slurred speech. During the examination, the patient exhibits a positive Romberg test and ataxia, along with vertical nystagmus.


LABORATORY STUDIES



Audiogram: 35 dB (normal: 0-25 dB)

Electronystagmography (ENG):
• Calibration: Positive, spontaneous vertical nystagmus

• Tracking test: Positive, left-sided horizontal nystagmus

• Positional test: Positive, dizziness associated with all head positions

• Caloric test: Negative (normal) to both cold and warm water

Visual evoked potential: 5 beats of nystagmus (normal: < 3 beats of nystagmus)

MRI: Eighth cranial nerve schwannoma arising within the internal auditory canal and involving the cerebellopontine angle


DIAGNOSIS


Vertigo from acoustic neuroma



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The patient’s symptoms are generally tied to the function of the vestibulocochlear nerve (cranial nerve VIII), which carries the afferent signals from the cochlea (hearing) and vestibular system (balance). Vestibular system disorders manifest as vertigo, often accompanied by nystagmus. This simultaneous occurrence of both of these deficits indicates a problem tied to the eighth cranial nerve.


The vestibular system is a complex sensory organ that determines both acceleration and position relative to gravity. There are three semicircular canals oriented at right angles to each other so that movement in all three planes in space can be detected. The hair cells of the crista ampullaris detect movement of the fluid within the semicircular canal and transmit this information along the sensory nerves of the vestibular system. The macula of the utricle and saccule contains small calcium carbonate stones that activate hair cells and thus detect the orientation of the head with respect to gravity as well as linear acceleration (Fig. 48-1).


image

FIGURE 48–1 Membranous labyrinth and organization of the crista ampullaris and the macula.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 48

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