Case 4 - A deaf man with poor balance Skye and Jackie

TRIGGER 1 A 28 year old man reports increasing tinnitus in his right ear with a tendency to fall to the right. He has no significant previous medical history. On examination he has right sided ataxia, a gaze paresis to the left and sensorineural deafness on that side. Q1 Where is the lesion?

Q1 Where is the Lesion? “The lesion is clearly involving the right pons, right side of the brainstem or cerebellum and presumably the 8th cranial nerve on the right given the deafness. It is therefore likely that the lesion is in the cerebellar pontine angle on the right” Q2 What is the lesion likely to be?

PDX: Acoutic Neuroma DDX: meningioma, developmental cysts, malignant middle ear infection, malignant otitis externa “Given the position the most likely cause of this is an acoustic neuroma which is a Schwannoma of the vestibular part of the 8th cranial nerve. There are a number of other lesions in this anatomical location that could give this clinical picture including meningiomas as well as different types of developmental cysts”. “Some patients develop malignant middle ear infections where the infection is such that it erodes the bone and destroys the local structures. In younger people this can take the form of cholesteatoma, in older patients especially diabetics it can often start in the external ear and they develop a malignant otitis externa”. Neuroscience at a Glance

Clinical Reasoning: Up-to-date Cochlear nerve —Symptomatic cochlear nerve involvement occurred in 95 percent of patients. The two major symptoms were hearing loss and tinnitus. Hearing loss was present in 95 percent but only two-thirds of these patients were aware of this limitation. Vestibular nerve — Involvement of the vestibular nerve occurred in 61 percent of patients. Affected patients frequently acknowledged having unsteadiness while walking, which was typically mild to moderate in nature and frequently fluctuated in severity. True spinning vertigo was uncommon. The most nondescript vertiginous sensations, such as brief tilting or veering, can suggest the presence of a vestibular schwannoma. Trigeminal nerve — Trigeminal nerve disturbances occurred in 17 percent of patients. The most common symptoms were facial numbness (paresthesia), hypesthesia, and pain. The average duration of symptoms was 1.3 years; the symptoms usually occurred after hearing loss had been present for more than two years and vestibular symptoms for more than one year. Facial nerve — The facial nerve was involved in 6 percent of patients. The primary symptoms were facial paresis BUT…. Q3 Why does he have a gaze paresis?

Gaze Paresis: a disturbance of eye conjugate movement in which gaze tends to be tonically deviated in the direction of normal gaze. For example, in left frontal lobe damage the patient cannot voluntarily look to the right and the eyes spontaneously deviate to the left. The patient may be able to return the gaze voluntarily to the midline but cannot move the eyes past the midline into the paretic field of gaze. “This reflects compression of the left pontine area in particular the pontine paramedian reticular formation which is responsible for horizontal gaze” Lesions of the sixth nerve nucleus cause paralysis of gaze to the side of the lesion. If fibers from the opposite 6th nerve nucleus are involved as they cross to the MLF, there is also weakness of the ipsilateral medial rectus muscle. NOTE: patients with hemisphere lesions look toward their lesion, while patients with pontine gaze palsies look away from their lesions. Note that patients with gaze palsy still have conjugate eye movements and therefore do not complain of diplopia. Q4 Would you initially do a lumbar puncture in this man to help in the diagnosis?

No indication for LP in this case. I.e. no infection, no suspected SAH, no instillation of chemotherapy. Q5 What (other) tests would be helpful in the diagnosis of this man?

Examination Physical examination. Identify other sources of symptoms and any concurrent disorders Otoscopic examination. Rule out other causes of hearing loss, assess general ear condition. Do not discontinue further investigation when eardrum is normal but there is unilateral hearing loss or tinnitus Complete neurologic examination. Pay special attention to the cranial nerves Summary of tests Audiometry to determine hearing loss and establish a baseline prior to further observation or therapeutic intervention: (1) pure tone, (2) speech discrimination (most often affected in patients with acoustic neuroma even when pure tone audiometry is normal), and (3) speech threshold MRI with gadolinium enhancement is the gold standard for diagnosis and should be performed early in the investigative process whenever possible. Can be done before referral to ENT specialist if MRI facilities are available. Expedites definitive diagnosis. (Fast spin echo MRI has also been investigated for the detection of acoustic neuroma, although it does not reliably identify small tumors) CT scan with contrast may be performed if necessary in cases where an MRI is not available or cannot be performed but it is limited to identifying tumors 1cm or greater in diameter Auditory brainstem response test may be done in some cases to determine interruption of electrical impulses through the auditory nerve to the brainstem. A negative result does not rule out acoustic neuroma. (Provides information about the transmission velocity of electrical impulses along the acoustic nerve from the inner ear to the brainstem pathways) Q6 Should his family be told they are at risk of developing similar problems?

No, as acoustic neuromas are rarely inherited. If they are bilateral in nature, however, this implies that they might have a condition called neurofibromatosis type II in which case genetic testing and counselling would be advised. Neurofibromatosis type 2 (NF2) is a dominantly inherited syndrome that predisposes individuals to multiple tumors of the nervous system. The most common of these are bilateral vestibular schwannomas; intracranial and spinal meningiomas and spine tumors are also a prominent component of this condition. Mutations in the NF2 gene, which produces merlin, a tumor suppressor, are responsible for this syndrome