Ataxia is incoordination or clumsiness of movement that is not the result of muscular weakness. Most commonly the term is only used to describe an unsteadiness of walking, but it is not correct since the same principles apply to disturbances in coordinated movements affecting the upper extremities, the speech mechanisms and the eye movements. Ataxia can result from cerebellar, vestibular or sensory ( proprioceptive ) disorders.
Is produced by lesions of the cerebellum itself or its afferent or efferent connections in the cerebellar peduncles, pons, or red nucleus.
Is produced by lesions anywhere along the peripheral eighth nerve pathway from labyrinth to brain stem and in the vestibular nuclei.
Can result from abnormalities anywhere along the afferent pathway from peripheral nerve, dorsal root, dorsal spinal funiculus, or the sensory projection from the thalamus to the parietal lobe cortex.
Clinical sings vary with the type of ataxia and within the same type. Nevertheless physical examination and history-taking are very important in the approach of a patient with ataxia, because each type possesses distincts features that may serve as clues to diagnosis. Some of this features are shown in (Table 1)
"The movements of my left arm are done subconsciously, but I have to think out each movement of the right (affected) arm. I come to a dead stop in turning and have to think before I start again."
Disorders of the cerebellum result in symptoms and signs described by Gordon Holmes from his studies of patients who sustained gunshot wounds to the cerebellum in the first World War. Holmes described three principal deficits.
1) Hypotonia - is a common finding, which results in defective posture maintenance and is manifest as a diminished resistance to passive limb displacements and a delay in the response to such rapid imposed movements. Limbs are easily displaced by relatively small force and, when shaken by the examiner, exhibit an increased range of excursion. When muscles are contracted against resistance that is then removed, the antagonist muscle fails to check the movement and compensatory muscular relaxation does not ensue promptly. This results in rebound movement of the limb ( Holmes' sign ).
2) Incoordination - include several distinctive defects: a delay in initiating responses with the affected limb, errors in the range and force of movement or dysmetria, and errors in the rate and regularity of movements. This last most readily demonstrated when the patient attempts to perform rapid alternating movements. Patients cannot sustain a regular rhythm, a sign called dysdiadochokinesia
3) Action or Intention tremor - The rate, rhythm, amplitude, and force of movements fluctuate, producing a jerky appearance. This irregularities are most pronounced during termination of movement which leads to an action tremor as the limb approaches the target.
The motor abnormality associated with cerebellar lesions depends on several anatomical and physiological principles which can guide the effort to localize disease processes to the cerebellum.
In this type of ataxia it is very important to look for symptoms and signs, such as vertigo and nystagmus, because they are often found in vestibular disorders. Nystagmus is frequently present, typically unilateral, and most pronounced on gaze away from the side of vestibular involvement. Another important find is that the vestibular ataxia is gravity-dependent, which means that incoordination of limb movements cannot be demonstrated when the patient is examined lying down but becomes apparent when the patient attempts to stand or walk. In addition, patients with vestibular dysfunction depend heavily on visual proprioception, so closing the eyes accentuates the gait disorder.
The functional defect results from an impaired perception of the location of the body part combined with relatively preserved strength in the member. Clinical findings include defective joint position and vibration sense in the leg and sometimes the arms, unstable stance with Romberg's sign, and a gait of slapping or steppage quality. Some examples of diseases that cause sensory ataxia are shown in the table below.
PolyneuropathyDiabetes Hypothyroidism Cisplatin Isoniazid Diphtheria |
MyelopathyAcute transverse myelitis Vacuolar myelopathy(AIDS)Multiple Sclerosis Vascular Malformations Tumor or Cord compression |
|---|
There is a lot of others diseases that can cause disorders of gait and equilibrium, such as spastic ataxia, frontal lobe disorders, hemiparesis and retropulsion. Nevertheless, their anatomical and physiological basis are very distinct, sometimes poorly understood, and are beyond the scope of this review.
Bibliography
Back to Neurology
Back to Specialties
Back to Medstudents' Homepage