Ataxia

Causes and PathogenesisTop

Ataxia is an impairment of motor coordination that makes it difficult to perform smooth and precise movements. It is due to disorders causing damage to the cerebellum or cerebellar systems (cerebellar ataxia) or damage to the afferent proprioceptive pathways at the level of peripheral nerves or dorsal columns of the spinal cord (sensory ataxia).

Causes of cerebellar ataxia:

1) Toxic (alcohol and drugs [eg, phenytoin, barbiturates, lithium]).

2) Vascular (ischemic or hemorrhagic stroke).

3) Infectious or postinfectious (viral cerebellitis, HIV infection, Creutzfeldt-Jakob disease).

4) Inflammatory (multiple sclerosis, ataxia associated with anti–glutamic acid decarboxylase [GAD] antibody, glucocorticoid-responsive encephalopathy associated with autoimmune thyroiditis).

5) Neoplastic (metastatic tumors, primary tumors, paraneoplastic syndromes).

6) Metabolic (vitamin E deficiency, vitamin B1 deficiency [Wernicke encephalopathy], celiac disease, hypothyroidism, hypoparathyroidism).

7) Neurodegenerative (multiple system atrophy, cerebellar type; Wilson disease; spinocerebellar ataxias; Friedreich ataxia [mixed cerebellar and sensory ataxia]).

8) Structural (Arnold-Chiari malformation).

Causes of sensory ataxia:

1) Toxic (drug-induced neuropathy [vincristine, isoniazid], neuropathy related to heavy metal poisoning).

2) Infectious (tabes dorsalis [neurosyphilis-related degeneration of posterior columns of the spinal cord]).

3) Inflammatory (Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, Sjögren syndrome–related neuronopathy [damage to dorsal root ganglia], spinal cord lesions in multiple sclerosis).

4) Neoplastic (paraneoplastic neuronopathies, neuropathy secondary to monoclonal gammopathy).

5) Metabolic (diabetic neuropathy, subacute combined degeneration [vitamin B12 deficiency]).

6) Neurodegenerative (Friedreich ataxia).

DiagnosisTop

1. History and physical examination:

1) Cerebellar ataxia:

a) Appendicular ataxia (dysmetria [abnormal finger-to-nose and heel-to-shin tests, overshooting or undershooting with finger chase]).

b) Dysdiadochokinesia (irregular amplitude and rhythm with rapid alternating movements [eg, pronating and supinating the forearm]).

c) Tremor (often intention tremor [increased amplitude of tremor as the limb nears the target]).

d) Axial ataxia (wide-based gait, truncal titubation).

e) Dysarthria (slurred speech, scanning speech).

f) Abnormal eye movements (ocular dysmetria [overshooting or undershooting with saccades], nystagmus).

2) Sensory ataxia: Loss of proprioception, symptoms of peripheral nerve or spinal cord damage, positive Romberg test (stand behind the patient ready to catch them in case of fall and ask the patient to stand erect with the feet together, arms stretched forward, and eyes closed; the test is positive if the patient begins to fall).

Differentiation between cerebellar and sensory ataxia: Table 1.

2. Diagnostic studies: Investigations depend on the presumed neurologic localization and pathophysiology and may include brain imaging studies (computed tomography [CT], magnetic resonance imaging [MRI]) in cerebellar ataxia, MRI of the spinal cord in sensory ataxia (in the case of suspected dysfunction of the dorsal columns of the spinal cord), and electrophysiologic studies (in case of suspected peripheral neuropathy). Other studies depend on the suspected cause.

TablesTop