Applied physiology
The physiology
of balance is complex (Fig. 14.1).
The body’s
sense of equilibrium is maintained by input from a number of sources. These include the eyes, proprio- ceptive organs especially in the muscles and joints of the neck, peripheral nerves, the labyrinth or ‘balance
organ’ in the inner ear which includes
the vestibule and semicircular canals and the cerebral cortex and cerebellum. Input from all these sources converges in the brain stem; dysfunction of any of these systems
may lead to
imbalance, a feeling
of unsteadiness, ‘vertigo’ – a sensation of movement
– and a
tendency to fall. Vertigo may be accompanied by ‘nystagmus’ – a rapid beating of the eyes to one side as impulses from the brain stem to the ocular muscles at- tempt
to correct the patient’s balance. Balance
disorders are common,
particularly in the elderly. They can be extremely
disabling, restricting patients’ ability to look after themselves and causing great distress. ‘Dizzy’ patients often
believe they have developed a serious and incurable disease but most cases are due to benign and often self-limiting
pathology.
Diagnosis
Some of the main causes are listed in Table 14.1. The diagnosis of the cause of vertigo or
imbalance depends mostly on history, much on examination and lit- tle on
investigation. Patients will use various terms to describe their imbalance including ‘dizziness’, ‘vertigo’, ‘funny turns’ and giddiness’. A careful history is by far the most important
aspect of assessing balance disorders. Patients
can mean very different things by
the terms they use so take time to listen to and understand exactly what
sensation the patient is complaining of. Pay particular
Figure 14.1 The control of balance. Source: Munir and Clarke 2013. Ear, Nose and Throat at a Glance. With permission of John Wiley & Sons Ltd.
Common specific disorders
****Benign paroxysmal positional vertigo
In benign paroxysmal positional vertigo (BPPV) short-lived (often a few sec- onds) attacks of vertigo are precipitated by turning the head, especially when the patient is in bed. A sensation that the head is ‘spinning’ occurs following a latent period of several seconds. This is thought to be due to a degenerative condition of the utricle of the inner ear which causes calcified particles to shear off the highly specialized neuro-epithelium. BPPV may occur spontaneously or following head injury. It is also seen in chronic otitis media. The symptoms can be reproduced by rapidly turning the patient’s head while she is lying on an ex- amination couch with her head gently lowered below the head of the couch and supported firmly by the examiner (Hallpike Positional Manoeuvre). Nystagmus will be seen but repeated testing results in abolition of the vertigo. Steady reso- lution of BPPV is to be expected over a period of weeks or months. It may be recurrent.
Treatment
BPPV can often be relieved completely by the Epley or ‘particle repositioning’ manoeuvre. This is a series of sequential controlled movements of the head usually carried out by a skilled audiologist which is said to work by dislodging calcified particles (‘otoliths’) within the inner ear fluids.
****Menière’s disease
Menière’s disease is fortunately uncommon, but may be incapacitating. This is a condition of unknown aetiology but interest has focused on distension of the structures in the inner ear by retained fluid. There is a typical triad of symptoms of vertigo, deafness and tinnitus. The attacks can last from a few hours to several days. Vomiting is common during attacks. It can occur at any age, but its onset is most common between 40 and 60 years. It usually starts in one ear, but the second be- comes affected in 25% of cases. Although deafness is fluctuant repeated attacks can cause significant sensorineural hearing loss. Tinnitus may be constant but is more severe before an attack.
Treatment
Medical
Anti-emetics and labyrinthine sedatives are helpful in an acute attack, but if the patient is vomiting oral medication is of limited value. Cinnarizine and
prochlorperazine are useful. Prochlorperazine can be given as a suppository or sublabially, or chlorpromazine may be given as an intramuscular injection. Between attacks, various methods of treatment are used but the evidence for their efficacy is weak. They include:
• fluid and salt restriction;
• avoidance of smoking and excessive alcohol or coffee;
• regular therapy with betahistine hydrochloride;
• labyrinthine sedatives, e.g. cinnarizine or prochlorperazine;
• low-dose diuretic therapy.
Surgical
Some ENT surgeons will offer surgery for patients with severe disabling Menière’s disease which cannot be controlled by the above measures. Techniques include labyrinthectomy but as this destroys the hearing it is only considered in unilateral cases and when the hearing is already severely impaired. An alternative is the instillation of an ototoxic drug such as gentamycin into the inner ear. There is a significant risk to hearing with this technique. Surgical division of the vestibular nerve preserves the hearing but is a hazardous procedure.
****Vertebrobasilar insufficiency
Ischaemia in the part of the brain supplied by the vertebrobasilar artery can cause momentary attacks of vertigo. These are typically precipitated by neck extension, e.g. hanging washing on a line. The diagnosis is more certain if other features of brain stem ischaemia such as dysarthria or diplopia, are present. Severe ischaemia may cause ‘drop attacks’ without loss of consciousness.
****Ototoxic drugs
Ototoxic drugs, such as gentamycin and other aminoglycoside antibiotics, can cause disabling and permanent loss of balance by destruction of labyrinthine function. The risk is reduced by careful monitoring of serum levels of the drug, especially in patients with renal impairment. There is not usually any rotational vertigo, just a sensation of poor balance control (ataxia).
****Acute labyrinthitis
Acute suppurative or pyogenic labyrinthitis causes severe vertigo and total loss of hearing. This can complicate otitis media. The term ‘acute labyrinthitis’ is also used to describe a sudden onset of vertigo of unknown aetiology associated with vomit- ing and in severe cases collapse. Nystagmus is a prominent feature. The structures in the labyrinth include both the vestibule, which is concerned with balance and the cochlea. If the hearing is unaffected it is assumed that rather than affecting the entire labyrinth the cochlea is spared and the term vestibular neuronitis is used. A viral cause is often assumed. Some cases may be due to a vascular event. To emphasize the uncertainty over aetiology many authors prefer the term ‘acute vestibular failure’ or ‘recurrent vestibulopathy’. Management is similar to that of Menière’s disease in the acute phase. Improvement takes place over a period of weeks and is quicker in younger patients. There may be residual imbalance which can take months or years to resolve.
****Trauma to the labyrinth
Trauma to the labyrinth causing vertigo may complicate head injury, with or without temporal bone fracture. Vertigo may occur after ear surgery and will usually settle in a few days.
CLINICAL PRACTICE POINT
• Acute loss of balance is extremely frightening. Many patients will suspect they have developed a brain tumour or some serious disease but most of the causes of balance disorders are benign.
Treatment of balance disorders
• Treat the underlying cause if you can, e.g. cardiovascular disease, epilepsy.
• Antihistamines and vestibular ‘sedatives’ can be used in acute attacks.
• BPV often responds well to ‘Epley’s Manouvre’.
• Surgery has a very limited role.
• Antihistamines and vestibular ‘sedatives’ can be used in acute attacks.
• BPV often responds well to ‘Epley’s Manouvre’.
• Surgery has a very limited role.
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