Sensory ataxia

Sensory ataxia is a form of ataxia (loss of coordination) caused not by cerebellar dysfunction but by loss of sensory input into the control of movement ¹. Ataxia is defined as impaired coordination of voluntary muscle movement, is a physical finding, not a disease. Sensory ataxia leads to a lack of muscle movement coordination caused by a loss of the sense of where different parts of the body are located in relation to each other and the ground. Sensory ataxia leads to unsteady walking and, in particular, may affect the ability to balance in the dark or with closed eyes (in situations such as showering). Subjects with sensory ataxia may walk with a high-stepping gait (due to associated motor weakness) or feet-slapping gait (to assist with sound-induced sensory feedback). Pseudoathetosis (random finger movements seen on outstretched hands with eyes closed) may also occur in sensory neuronopathy affecting the upper limbs ².

Sensory ataxia is caused by damage to the nerves that send constant feedback from the position sensors in the joints and muscles to the movement control center in the brain.

Sensory ataxia is distinguished from cerebellar ataxia by the presence of near-normal coordination when the movement in question is visually observed by the patient, but marked worsening of coordination when the eyes are closed.

Sensory ataxia also lacks the associated features of cerebellar ataxia such as pendular tendon reflexes, scanning dysarthria, nystagmus and broken pursuit eye movements.

Patients with sensory ataxia often demonstrate pseudoathetosis and Romberg’s sign. They usually complain of loss of balance in the dark, typically when closing their eyes in the shower or removing clothing over the head.

Sensory ataxia is present in sensory peripheral neuropathies and conditions causing dysfunction of the dorsal columns of the spinal cord such as tabes dorsalis.

Sensory ataxia causes

Sensory ataxia is generally caused by damage to nerves in the spinal cord or nerves leading to the extremities, such as the feet and legs. Loss of sensation in the feet, hands and torso caused by nerve damage can result from systemic diseases such as diabetes and multiple sclerosis, spinal cord compression, exposure to toxins such as lead, mercury and arsenic, and a number of other conditions.

Common causes of sensory ataxia:

• Brain hemorrhage
• Cerebral palsy
• Diabetes mellitus
• Friedreich ataxia
• Guillain-Barré syndrome
• Head trauma
• Hereditary sensorimotor neuropathy type 3
• Multiple sclerosis
• Peripheral neuropathies
• Porphyria
• Sensory neuropathy
• Spinal cord compression
• Stroke
• Tabes dorsalis
• Toxic reaction
• Vitamin E deficiency
• Vitamin B-12 deficiency
• Thiamine or vitamin B1 deficiency

Sensory ataxia symptoms

Due to the loss of sensation in the feet and legs in sensory ataxia, sufferers develop an unsteady, possibly stomping gait, with the foot striking the ground hard on each step, which is sometimes described as ‘walking on pillows’. It may also be associated with pain in the feet and legs. Characteristically, the patient looks down and walks as if throwing his or her feet, which tend to slap on the ground. Smooth, familiar routes cause less trouble than uneven, rough ones.

With less feedback on the position of the feet and legs in relation to the environment, the brain depends more highly on visual information to assess body position, so unsteadiness and imbalance become more pronounced with closed eyes or in low light.

In addition, subjects with sensory ataxia will have a positive Romberg sign. Romberg’s sign is inability to stand for 60 seconds with feet together and eyes closed. Romberg’s sign is a finding in patients with tabes dorsalis who have severe sensory ataxia from syphilitic damage to the dorsal columns of the spinal cord. In one study, every healthy person and more than half of the patients with cerebellar ataxia could maintain this position for 60 seconds, whereas half of the patients with sensory ataxia lasted only 10 seconds before beginning to topple over.

Sensory ataxia diagnosis

Most cases of sensory ataxia can be diagnosed clinically using a combination of strategies that may include medical history, family history, and a complete neurological evaluation including checking your memory and concentration, vision, hearing, balance, coordination, and reflexes, but occasionally nerve conduction studies are required.

If you have ataxia, your doctor will look for a treatable cause. Besides conducting a physical exam and a neurological exam, your doctor might request laboratory tests, including:

• Imaging studies. A CT scan or MRI of your brain might help determine potential causes. An MRI can sometimes show shrinkage of the cerebellum and other brain structures in people with ataxia. It may also show other treatable findings, such as a blood clot or benign tumor, that could be pressing on your cerebellum.
• Lumbar puncture (spinal tap). A needle is inserted into your lower back (lumbar region) between two lumbar bones (vertebrae) to remove a sample of cerebrospinal fluid. The fluid, which surrounds and protects your brain and spinal cord, is sent to a laboratory for testing.
• Genetic testing. Your doctor might recommend genetic testing to determine whether you or your child has the gene mutation that causes one of the hereditary ataxic conditions. Gene tests are available for many but not all of the hereditary ataxias.

Sensory ataxia treatment

The main focus of sensory ataxia treatment is to try and halt progress of the nerve damage, alleviate symptoms, increase independence and minimize the risk of falls. If a cause is found, then treatment, where possible, will address the underlying cause. For example, vitamin B12 deficiency is treated with vitamin B12 supplementation (typically starting with injections then switching to oral); diabetic neuropathy is managed by maintaining tight sugar control. Regardless of the cause of neuropathy, balance and gait are often improved by physical therapy.

Treatment may involve referral to an occupational therapist, who can make adjustments to the home environment and suggest ways to make daily living activities easier. Specialist, balance physiotherapy and the use of mobility aids may also be necessary and special medications can be prescribed to control pain of nerve origin, if necessary.

Adaptive devices

Ataxia caused by conditions such as multiple sclerosis or cerebral palsy might not be treatable. In that case, your doctor may be able to recommend adaptive devices. They include:

• Hiking sticks or walkers for walking
• Modified utensils for eating
• Communication aids for speaking

Sensory ataxia physiotherapy treatment

You might benefit from certain therapies, including:

• Physical therapy to help your coordination and enhance your mobility
• Occupational therapy to help you with daily living tasks, such as feeding yourself
• Speech therapy to improve speech and aid swallowing

Research has shown that transcranial magnetic stimulation may help improve gait and postural control in people with ataxia, but more research is needed. Some studies have indicated that aerobic exercise also may be beneficial for some people with idiopathic ataxic syndromes.

Living with sensory ataxia

Living with sensory ataxia involves working with physiotherapists and occupational therapists to ensure safe mobility and to maintain as much independence as possible. This may include using mobility aids, adjusting the home environment and making lifestyle adjustments (such as alcohol avoidance) to make daily activities easier.

Sensory ataxia prognosis

Sensory ataxia prognosis depends on the underlying cause. For acquired ataxias, after the offending factor is removed, the disease progression normally stops and the patient will recover in 6 months to a year. With early intervention, especially at a young age, most patients compensate well and will only have very mild incoordination or none at all.

References

1. Lu KY, Yuen KF, Luo JY, Hong CZ, Chou LW. Therapeutic effects of acupuncture on sensory ataxia after a cerebral hemorrhage: A case report. Medicine (Baltimore). 2020;99(29):e21124. doi:10.1097/MD.0000000000021124 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7373561
2. Ashizawa T, Xia G. Ataxia. Continuum (Minneap Minn). 2016;22(4 Movement Disorders):1208-1226. doi:10.1212/CON.0000000000000362 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5567218