NYSTAGMUS
Why not consider the differential diagnosis of nystagmus under vertigo,
because anatomic pathophysiology is the key to the differential in
both? The reason is that there are two forms of nystagmus (ocular and
cerebellar) that do not necessarily occur with vertigo. In addition to these
two categories, nystagmus that usually occurs with vertigo is divided into
nystagmus of middle ear diseases, nystagmus of inner ear diseases, nystagmus
due to auditory nerve involvement, and nystagmus due to brainstem and
cerebral diseases.
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Ocular nystagmus. This is a pendular to-and-fro nystagmus with
no fast component, which is usually due to congenital visual defects but
which may be due to working in poor lighting (miner’s nystagmus). It is
really an effort of the eye to find a better visual image. Infants with
spasmus nutans have this type of nystagmus.
- Middle ear disorders. Nystagmus may result from otitis media,
which causes associated inflammation of the labyrinth.
- Inner ear diseases. Labyrinthitis may be viral, postinfectious,
traumatic, or toxic (e.g., from salicylates, quinine, streptomycin, or
gentamycin). A cholesteatoma also causes nystagmus, as does Ménière
disease.
- Auditory nerve. Acoustic neuromas, internal auditory artery
occlusions, or aneurysms and basilar meningitis may be considered in this
category. Diabetic neuritis is another cause.
- Brainstem. Transient ischemic attack (TIA) from basilar artery
insufficiency, multiple sclerosis, gliomas, syphilis, and tuberculosis are
the major conditions to consider here. Thrombi, emboli, and hemorrhages in
the branches of the basilar artery are important too. With TIA the
possibility of migraine and emboli from SBE or atrial fibrillation should be
investigated. Dissemination encephalomyelitis and other forms of
encephalitis should not be overlooked. Degenerative diseases such as
syringobulbia and olivopontocerebellar atrophy are possibilities.
- Cerebellum. In addition to the causes of nystagmus mentioned
under brainstem, the physician should consider cerebellar tumors, abscesses,
posterior fossa subdural hematomas, and diphenylhydantoin toxicity, as well
as Friedreich ataxia and other forms of hereditary cerebellar ataxia.
Alcoholic cerebellar degeneration is a significant cause of nystagmus. Acute
cerebellar ataxia of children cannot be forgotten. Platybasia may compress
the cerebellum and cause nystagmus. Cerebellar degeneration associated with
carcinoma of the lung is often misdiagnosed.
- Cerebrum. Curiously enough, frontal lobe tumors may cause
nystagmus. Head injuries, encephalitis, chronic subdural hematomas,
occipital meningiomas, and the aura of an epileptic seizure may also cause
nystagmus.
Approach to the Diagnosis
The workup here is similar to that of vertigo. Nystagmus without other
signs of central nervous system (CNS) disease is usually ocular or
peripheral in the middle or inner ear. Vertigo is almost invariably present
in nystagmus of aural origin. Nystagmus with long tract signs such as
hemiplegia or hemianesthesia is invariably brainstem in origin. Purely
cerebellar nystagmus is not easily fatigued and is associated with
dyskinesia and dyssynergia of the extremities as well as ataxia. There are
no long tract or cranial nerve signs. Nystagmus with vertigo, nausea,
vomiting, tinnitus, and deafness suggests Ménière disease.
Confirmation of the diagnosis is made by audiograms, caloric tests, skull
x-rays (with special views of the mastoids and petrous bones), angiography,
CT scans, and myelography. MRI scans are useful, especially in diagnosing
brainstem lesions and multiple sclerosis. They also provide a better view of
the internal auditory canal. A spinal tap will help in the diagnosis of
multiple sclerosis and neurolues as well as acoustic neuromas.
