Ataxic disorders

Ataxia is a feature of disorders of the cerebellum and its connections. It may be found in a large range of neurological conditions, in some of which it is the principal or main feature, but clinical assessment is complicated by the fact that few ataxic patients have disease restricted to the cerebellum alone.

Clinical features

Symptoms—common presenting complaints are (1) gait unsteadiness—particularly with lesions of the vermis, (2) limb incoordination and tremor—particularly with lesions of the cerebellar hemisphere, (3) slurring of speech, and (4) visual and oculomotor symptoms, although these are rare in pure cerebellar disease.

Signs—these include (1) a broad-based gait with a poor turn, (2) scanning dysarthria, (3) limb ataxia—manifest as dysmetria and dysdiadochokinesis, (4) intention tremor, (5) abnormal eye movements.

Key points in differential diagnosis—(1) age of onset—early onset is before 20 to 25 years; (2) rate of onset and the nature of the progression of the illness; (3) other features of neurological involvement, which enables differentiation of the ‘pure’ ataxias from the ‘complicated’ ataxias.

Investigation and treatment—high-resolution imaging, genetic testing and other investigative tools enable a diagnosis to be made in over 50% of cases. The mainstay of management is supportive: there are no drugs that help cerebellar balance problems, but active engagement in physiotherapy can help to lessen the impact of the physical disorder.

Particular causes of ataxia

Ataxias with early onset—(1) acute and subacute ataxias with onset in childhood—should raise the possibility of infectious, para-infectious or vascular conditions; (2) chronic progressive ataxias of early onset—very often genetic in aetiology, typically autosomal recessive, with the commonest cause being Friedreich’s ataxia; a clear molecular genetic diagnosis can be established in some cases (e.g. abnormality of the frataxin gene in Friedreich’s ataxia).

Chronic progressive ataxia—causes include (1) genetic—with inheritance typically being autosomal dominant; (2) chronic alcohol abuse—probably the most common cause of progressive cerebellar degeneration in adults; (3) deficiency disorders—e.g. vitamin E; (4) toxic agents—drugs (e.g. phenytoin), solvents and heavy metals; (5) structural lesions in the posterior fossa; and (6) other—e.g. Wilson’s disease, other metabolic disorders. No cause can be found in many cases, labelled as ‘idiopathic late-onset cerebellar ataxia’, with the commonest pattern recognized being that of multiple system atrophy, where there is typically ataxia complicated by autonomic failure and (in some cases) Parkinsonism.

Rapid, subacute onset ataxia—should always raise the possibility of paraneoplastic or other inflammatory conditions.

Acute ataxia—the two main causes are (1) cerebellar haemorrhage—usually associated with headache, vertigo, vomiting, altered consciousness and neck stiffness; and (2) cerebellar infarction—in which cerebellar signs are usually combined with signs of brainstem ischaemia.