Cerebellar Ataxia

This is a disorder of coordination due to a lesion that affects the cerebellum. There are many possible aetiologies including vascular, space occupying lesion that may be neoplastic or infectious, hereditary or metabolic. Very rarely is cerebellar ataxia an isolated finding and almost all causes are associated with other lesions.

• Wernicke's encephalopathy is the commonest cause in adult life.
• Friedreich's ataxia is the commonest of the genetic causes, representing 50% of genetic cases.
• It affects between 1 and 2 in 100,000.
• It has a 10% incidence of diabetes mellitus and a further 10 to 20% have impaired glucose tolerance.

Symptoms

• Disturbance of gait is the commonest presenting feature. The patient may be unable to walk in a straight line or bump into things and it is often worse in the dark.
• Clumsiness carrying objects often precedes deterioration of handwriting. Midline lesions tend to cause problems of gait whilst lesions of the hemispheres cause ipsilateral incoordination.
• Dysarthria is staccato in nature.
• Vomiting or headache suggests a posterior fossa mass.
• An acute history suggests a cerebellar haemorrhage but a slower onset suggests a tumour or abscess.
• Vertigo is less common in the degenerative diseases.

Signs

• The patient may enter the room with a broad-based gait. A tandem walk (heel to toe) will demonstrate the problem. About 40% of patients with vermis lesions do not have limb ataxia but disturbance of gait.
• Limb ataxia can be demonstrated by getting the patient to touch his nose then your finger about 40cms away and repeated. An intention tremor overshoots or undershoots the target.
• Dysdiadochokinesis is demonstrated by getting the patient to tap the back of his hand rapidly or to pronate and supinate the hand rapidly.
• Nystagmus is demonstrated by holding the patient's head still and getting him to follow your finger, about 50cms away, to left and right without going too far to the extreme. The eyes drift slowly back to the centre followed by a rapid correction. The rapid correction is the aspect that is most readily noted but it is the slow drift that is pathological. The side of the lesion is the side of the slow drift and the opposite side to the rapid correction. Acute or subacute presentation with disordered eye movements should lead to suspicion of Wernicke's encephalopathy and requires urgent treatment with thiamine.
• Cerebellar dysfunction in an infant is easily overlooked. Intrauterine insults may not present with incoordination until the second year of life.
• An intention tremor occurs only on movement unlike the fine tremor at rest in essential tremor or thyrotoxicosis or the pill-rolling of Parkinson's disease.

The realistic list of possibilities will depend upon age of onset, family history, acute, subacute or chronic onset and associated features. Cerebellar ataxia rarely occurs in isolation.

• A very acute onset is associated with haemorrhage or obstruction of an artery. PICA (posterior inferior cerebellar artery) syndrome is an acute onset of headache, vomiting, nystagmus, altered consciousness and neck stiffness.
• A subacute reversible ataxia can occur in children between the ages of 2 and 10 due to viral infection. In older patients varicella or Guillain-Barre syndrome can produce the same.
• Other causes of subacute ataxia are hydrocephalus, foramen magnum compression, tumour or abscess. In addition, heavy metals, drugs, solvents and alcohol can be to blame.
• An episodic course may suggest hysteria but it does occur in multiple sclerosis, drug ingestion, TIA and a dominant inherited condition. Multiple sclerosis usually has other features too.
• In adults the commonest cause for a chronic picture is alcoholism.
• Paraneoplastic syndromes related to cancer of lung or ovary precede diagnosis of the malignancy in 70% of cases.
• Creutzfeldt-Jakob disease, especially nvCJD must be remembered. Isolated cerebellar ataxia can be the presenting feature of sporadic CJD.¹
• Wilson's disease may also cause cirrhosis or cardiomyopathy from deposition of copper.
• Hepatic encephalopathy, hyponatraemia and hypothyroidism are rare causes.
• There are degenerative diseases including the glycogen storage diseases.
• Of the inherited disorders the autosomal recessive ones tend to present before 20 and the dominant ones after that age. Ataxia telangiectasia and xeroderma pigmentosum have characteristic features. Onset is usually 8 to 15 years old. Muscular wasting occurs in 50% as does pes cavus. There are skeletal deformities in 85%. An abnormal ECG with T wave inversion occurs in 65%.
• About two thirds of cases presenting over 20 years old are idiopathic. They may develop other features too.

• LFTs and FBC may suggest alcohol abuse.
• A MRI scan is an extremely useful way to visualise the area.² It may show tumour, abscess, infarction, haemorrhage, demyelination or atrophy.
• It may be appropriate to search for a primary of lung or ovary.
• Abnormalities of copper metabolism occur in Wilson's disease.

Unless alcohol abuse can be swiftly diagnosed and treated, referral to Secondary Care will be required. There are many causes of this condition.

Non-Drug

Treatment depends upon the cause. In Wernicke's encephalopathy high dose thiamine is required, possibly parenterally. If alcohol consumption is chronic and high, sudden cessation can be dangerous and plans must be made for detoxification.

Drugs

• Where relevant, monitor blood levels of phenytoin.
• Antineoplastic drugs may need to be considered as the culprit and possibly changed.
• Chelating agents might help in heavy metal toxicity.
• By and large, drugs have nothing to offer in terms of controlling cerebellar ataxia but there are some early reports of a 5-HT1A agonist being of value in some conditions.³

Prognosis depends upon the cause of the condition.

• Wernicke's encephalopathy may be reversible as may the viral cases but most causes are not.
• Most patients with idiopathic late-onset cerebellar ataxia lose the ability to walk in 5 to 20 years with a slight truncation of their lifespan by immobility.
• The prognosis is worse in those who show brainstem atrophy on MRI.