Aetiology

Balance disorders may be caused by disorders at the level of the vestibular apparatus, cerebellum or brainstem, extrapyramidal, spinal cord, or neuromuscular system.

Vestibular

Unilateral vestibulopathies or bilateral asymmetric vestibulopathies are associated with vestibular tone imbalance that causes the patient to experience true vertigo. This may be associated with nausea and vomiting. Vestibular tone imbalance is self-limited, and vertigo subsides, but if central compensation does not occur there may be a persisting feeling of disequilibrium or difficulty with balance. Drop attacks may occur, which differ from syncopal episodes in that altered level of consciousness occurs with syncopal episodes.

Causes of unilateral peripheral vestibular loss:

  • Vestibular neuritis: this is a common condition usually following a viral infection and thought to be due to inflammation of the vestibular nerve.[3][4]​​ Labyrinthitis is a similar condition due to inflammation of the labyrinth.

  • Vestibular concussion.

  • Vestibular schwannoma (acoustic neuroma): benign tumour arising from Schwann cells in the vestibular portion of the eighth cranial nerve in the cerebello-pontine angle.[5]​ These tumours are relatively uncommon.[6]

  • Meniere's disease: results in episodic vertigo associated with unilateral fluctuating sensorineural hearing loss, tinnitus, and ear fullness or pain and may cause drop attacks in addition to episodes of vertigo.[7][8]

  • Multiple sclerosis can, rarely, present with a plaque at the root entry zone of the eighth cranial nerve, mimicking a peripheral vestibular presentation.[9][10]

Inappropriate peripheral vestibular activation or excitation can also cause dizziness and balance difficulty. Causes of inappropriate peripheral vestibular activation include:

  • Benign paroxysmal positional vertigo (canalithiasis): results in brief episodes of transient vertigo related to change in head position or a constant feeling of disequilibrium and problems with balance. This is a comparatively common condition, particularly in older people. The most common variants are thought to be due to abnormal debris in either the posterior or lateral semicircular canal.[11]

  • Superior canal dehiscence: caused by an opening in the bone overlying the superior semicircular canal within the inner ear that results in fluid in the membranous superior canal being displaced by sound and pressure stimuli, which effectively acts as a third mobile window into the inner ear, causing vestibular excitation. Vestibular and/or auditory signs and symptoms include brief episodes of vertigo precipitated by coughing, sneezing, straining, or sudden loud noise with autophony and a feeling that the affected ear is blocked; may also cause drop attacks.[12]

Bilateral symmetric peripheral vestibular loss results in disequilibrium that is most prominent when the person is moving, as this is when vestibular signals are relied on the most. Balance is impaired due to compromised vestibulo-spinal reflexes. Blurring of vision or oscillopsia may occur due to compromised vestibulo-ocular reflex function that is needed to stabilise vision during head movement.

Causes of bilateral peripheral vestibular loss:[13][14][15]

  • Iatrogenic (e.g., ototoxic medicines)

  • Idiopathic, or congenital

  • Wernicke's encephalopathy (thiamine deficiency)

  • Infectious aetiologies (e.g., meningitis, syphilis, Lyme disease)

  • Autoimmune inner ear disease

  • Degenerative (age-related) inner ear disease.

Dandy-Walker's syndrome: a rare clinical presentation of bilateral peripheral hypofunction (ataxia and oscillopsia) with total loss of inner ear balance function involving both ears. It is caused by infection or trauma and presents initially with severe dizziness, but eventually the patient's eyes, muscles, and joints help them to compensate; most patients do quite well, except in the dark (loss of visual cues) or when walking on uneven or compliant surfaces (compromised proprioception).

Cerebellum

The cerebellum is important in the co-ordination of eye movements and movements of the limbs and trunk. Conditions giving rise to balance disorders include:[16]​

  • Cerebrovascular disease

  • Infectious disease (cerebellitis)

  • Demyelinating disorders such as multiple sclerosis, which may present as an acute cerebellar syndrome

  • Chronic or progressive cerebellar dysfunction: may result from posterior fossa tumours or other structural lesions such as Chiari malformations.

  • Non-structural causes of progressive cerebellar dysfunction: degenerative disease and systemic disease including vitamin E deficiency, coeliac disease, and paraneoplastic syndrome.

  • Inherited disorders such as the spinocerebellar ataxias, where cerebellar disease is accompanied by nystagmus, ocular motor abnormalities, and variable additional signs specific to genetic sub-types: for example, areflexia, upper motor neuron signs, sensory neuropathy, and/or retinal degeneration.[17][18]

  • Degenerative: cerebellar ataxia may be associated with bilateral peripheral vestibular hypofunction.[19]

Brainstem

Brainstem lesions involving projections from the cerebellum can also lead to cerebellar dysfunction. Central vestibular pathways in the brainstem, including the vestibular nuclei at the pontomedullary junction, contribute to balance control. The brainstem also contains structures that control eye movements and bulbar function (speech and swallowing). Motor and sensory long tracts through the brainstem may also be affected.

Brainstem lesions should be suspected when the balance disorder is associated with:

  • Diplopia

  • Dysarthria

  • Dysphagia

  • Weakness or sensory symptoms in the extremities.

Brainstem syndromes include:

  • Spinocerebellar ataxia

  • Vestibular migraine: unexplained dizziness or balance difficulty associated with headache and other symptoms of migraine such as nausea, photophobia, phonophobia, osmophobia, or visual aura, but in about half of cases the vertigo may occur without associated headache.[20] Migraine sufferers are also more prone to motion sickness.[21]

  • Mal de debarquement (MDD) syndrome: chronic disequilibrium following an ocean cruise or following prolonged travel by automobile or aeroplane with onset of symptoms occurring after the person disembarks. May result from a maladaptive response to a changing motion environment and most commonly affects middle-aged women.[22]

Brainstem disorders may also be caused by:

  • Vascular disease such as infarct or haemorrhage

  • Vascular malformation

  • Tumour

  • Demyelinating disease. Multiple sclerosis with lesions affecting the brainstem may cause vertigo, hearing loss, weakness, impaired sensation evolving over hours to days.[23]

  • Brainstem encephalitis

  • Metabolic derangement, as occurs with central pontine myelinolysis or Wernicke's encephalopathy.

Extrapyramidal

Impaired balance may be an early manifestation of an akinetic rigid syndrome as seen with the following extrapyramidal disorders:

  • Idiopathic Parkinson's disease: postural instability is a key feature but bradykinesia, rigidity, and tremor may be subtle early in the course of the disease and the clinician should carefully examine for these signs.[24]

  • Progressive supranuclear palsy: should be considered when parkinsonism is associated with abnormal ocular motility (especially vertical eye movements), speech difficulty (bulbar palsy), and upper motor neuron signs; falls occur early in the course of the disease.

  • Multiple system atrophy:

    • Striatonigral degeneration: consider in patients with parkinsonism that does not respond to medical treatment.

    • Shy-Drager syndrome: parkinsonism associated with autonomic nervous system dysfunction raises the possibility of Shy-Drager syndrome.

  • Corticobasal degeneration: parkinsonism may be a feature, as well as abnormal motor function (dystonia, myoclonus, alien hand syndrome) and cognitive dysfunction.

  • Normal pressure hydrocephalus: consider in patients with progressive gait difficulty (magnetic gait), cognitive decline, and urinary incontinence.[25]

The following secondary causes of parkinsonism must be considered in atypical cases:[26][27]

  • Medicines (e.g., antipsychotics or anti-emetics that block dopamine)

  • Vascular disease that may result in lower-body parkinsonism

  • Structural lesions such as hydrocephalus, subdural haematomas, or convexity meningiomas

Spinal cord

Spinal cord disease may result in impaired balance by disrupting proprioception and vestibulospinal reflexes in addition to affecting motor function by causing weakness or spasticity.

Acute spinal cord injury may be caused by:

  • Trauma

  • Compression by a mass such as a herniated disc

  • Demyelinating disease such as neuromyelitis optica variant of multiple sclerosis

  • Inflammatory disorders such as SLE.

Progressive spinal cord disease (myelopathy) may be caused by:

  • Intrinsic or extrinsic tumours

  • Infectious disease (syphilis [tabes dorsalis], tuberculosis, HIV, human T-lymphotropic virus [HTLV]-1)

  • Degenerative spine disease (spondylosis)

  • Demyelinating disease (chronic progressive multiple sclerosis).

Neuromuscular

Peripheral neuropathy involving large sensory fibres results in loss of proprioception from the lower extremities and sensory ataxia. If motor nerves are involved then lower extremity weakness may contribute to difficulty with gait.

Causes of peripheral neuropathy include:[28][29][30][31]

  • Diabetes mellitus

  • Deficiencies in vitamin B12 or vitamin E

  • Guillain-Barre syndrome or acute inflammatory demyelinating polyradiculopathy

  • Miller Fisher syndrome (triad of ataxia, areflexia, and ophthalmoparesis), considered a variant of Guillain-Barre syndrome and is associated with anti-GQ1b antibodies

  • A component of an inherited syndrome such as a spinocerebellar ataxia.

Medicines

Medicines and prescribed drugs (as well as recreational substances) that commonly cause dizziness and balance difficulty include:[32][33]

  • Aminoglycosides - ototoxicity

  • Cisplatin - ototoxicity

  • Anticonvulsants (carbamazepine, phenytoin, primidone, and some second-generation anticonvulsant drugs) - central nervous system (CNS) toxicity

  • Tranquilisers (barbiturates, antihistamines) - vestibular/CNS depressants

  • Antihypertensives and diuretics - hypotension

  • Amiodarone - CNS toxicity, peripheral neuropathy

  • Alcohol - cerebellar and vestibular dysfunction

  • Methotrexate - CNS toxicity, anaemia.

Miscellaneous

Dizziness and balance difficulty might also result from psychiatric disease, especially panic or anxiety disorders. However, patients with vestibular disorders also have a higher prevalence of panic and anxiety disorders.

It is also important to consider that the cause of the balance disorder might be multifactorial. For example, an individual with alcohol use disorder might have problems with balance due to alcohol-related neuropathy, alcohol-related cerebellar degeneration, and bilateral vestibulopathies from thiamine deficiency. In older patients there might be no identifiable cause.

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