11th August 2024

Ataxia

Ataxia is the loss of coordination, which can cause gait, speech, swallow and balance problems. It is not a specific diagnosis, but a neurological sign which can develop due to damage to a number of different areas within both the peripheral and the central nervous systems. Ataxia due to dysfunction of the cerebellum or its tracts is considered a movement disorder, whereas sensory (peripheral or dorsal column lesions) and vestibular ataxias result in disorders of movement but would not be cared for by a movement disorders specialist.

Sensory ataxia

Sensory ataxia will only briefly be covered here as it is not a movement disorder. It develops due to damage to the somatosensory nerves, inhibiting sensory feedback and therefore proprioception.

Sensory ataxia can be due to peripheral sensory neuropathies or spinal lesions. Peripheral neuropathies are commonly due to diabetes or alcohol excess, but can also be due to nutritional deficiencies, or metabolic, genetic, toxin, vascular and autoimmune causes. Spinal causes are due to damage to the dorsal column of the spinal cord, including tabes dorsalis secondary to syphilis, subacute combined degeneration of the spinal cord due to B12 deficiency (or functional B12 deficiency, as in nitric oxide poisoning), and vascular causes. Gluten ataxia describes ataxia in the presence of the antibodies of gluten sensitivity or coeliac disease, and may occur without gastrointestinal symptoms. Coeliac testing is therefore recommended in those who have unexplained peripheral neuropathies or ataxia.

Cerebellar disease

Cerebellar disease gives a specific set of findings remembered by the acronym ‘DANISH’: dysdiadochokinesia, ataxia, nystagmus, intention tremor, slurred speech and hypotonia. The ataxia can manifest as a wide-based gait, difficulty with the heel-to-shin test, past-pointing and slow hyper and hypometric saccades.

The causes of cerebellar disease can be split into genetic and non-genetic. Non genetic causes include:

• Vascular: stroke
• Autoimmune: MS, immune-mediated (Miller Fisher syndrome), paraneoplastic
• Metabolic: thiamine deficiency, hepatic encephalopathy
• Toxin: alcohol, gluten in coeliac disease
• Infectious: syphilis
• Degenerative: MSA-C

We will focus on a few genetic conditions in more detail.

Spinocerebellar ataxia

Spinocerebellar ataxias (SCA) are a large, complex group of over 20 inherited degenerative conditions presenting with progressive cerebellar ataxia, and named numerically in order of discovery (SCA1, SCA2 etc.). Alongside cerebellar syndromes, the various SCAs can also present with movement disorders, peripheral neuropathies, cognitive impairment, oculomotor/retinal/bulbar symptoms and pyramidal signs. Like Huntington’s disease they are mostly caused by triplet repeats with autosomal dominant inheritance. Most SCAs present in adulthood, however some can present in childhood. Treatment aims to reduce symptoms and maximise function as there are no cures.

Friedreich’s ataxia

Friedreich’s ataxia is an autosomal recessive progressive ataxia due to mutations in the frataxin gene. It is the most common hereditary ataxia and has a mean age of onset of 14 years. It is due to abnormal iron metabolism in the mitochondria leading to increasing cell death over time. It particularly affects the heart, pancreas, and nervous system (specifically the cerebellum, spinal cord and peripheral nerves), and leads to hypertrophic obstructive cardiomyopathy (90%), diabetes and ataxia/loss of proprioception/weakness. The cardiac complications are the leading cause of death.

The first and classical feature is ataxia with gait disturbance. Other symptoms include ataxia of the trunk and limbs, which may be described by the patient as ‘general clumsiness’, cerebellar dysarthria, loss of tendon reflexes with upgoing plantars, and a sensory neuropathy with distal loss of proprioception and vibration sensation, but typically preservation of pain and temperature sensation. Later features include motor weakness, more prominently of the lower limbs, and optic and vestibular atrophy. Other findings include scoliosis. There is generally no cognitive impairment.

There is currently no cure or effective treatment for the disease, so focus is on managing complications, in particular  cardiac involvement given the high associated mortality, and helping individuals maintain a normal level of function for as long as possible.

Ataxia telangiectasia

Ataxia telangiectasia is another autosomal recessive ataxia, similar to Fredrich’s ataxia. It is one of the inherited combined immunodeficiency disorders that begins early in childhood. As the name suggests, it causes a progressive cerebellar ataxia resulting in most affected individuals requiring a wheelchair by adolescence, and telangiectasias, spider-like clusters of dilated capillaries most commonly seen around the eyes and cheeks. In addition, it results in  recurrent infections (IgA deficiency) and an increased risk of cancer (10-30% lifetime risk), in particular lymphoma and leukaemia.