Ataxia and gait disturbances may be symptoms of many disease processes and generally are not themselves diagnoses. Ataxia is uncoordinated movement. A gait disorder is an abnormal pattern or style of walking. The presenting problem may be articulated by the patient or family as weakness, dizziness, stroke, falling, or another nonspecific chief complaint. Such symptoms must always be viewed in the context of the patient’s overall clinical picture. This chapter reviews the more common causes of acute ataxia and gait disorders (Table 169-1).

Clinicians erroneously tend to think that ataxia and gait disorders result primarily from cerebellar lesions. However, such disorders result from many systemic or focal conditions that affect different elements of the central and peripheral nervous systems. Cerebellar lesions may indeed cause ataxia, but isolated lesions of the cerebellum are not the most common cause of these complaints. Ataxias are classified as either motor (cerebellar) or sensory.

MOTOR ATAXIAS

Motor ataxias (also referred to as cerebellar ataxias) are usually caused by disorders of the cerebellum. The sensory receptors and afferent pathways are intact, but integration of the proprioceptive information is faulty. Involvement of the lateral cerebellum (one of the cerebellar hemispheres) may lead to a motor ataxia of the ipsilateral limb. Lesions affecting primarily the midline portion of the cerebellum often cause problems with axial muscle coordination, which is reflected in difficulty maintaining a steady upright standing or sitting posture.

There are many reports of lesions in what would seem to be unlikely locations producing motor ataxia. Supratentorial infarctions, particularly small, deep infarctions, and lacunae of the posterior limb of the internal capsule have been reported to cause isolated hemiataxia. It is postulated that interruption of either ascending or descending cerebellar to cortical pathways are the cause of this motor-type ataxia.¹ Small infarctions or hemorrhages in thalamic nuclei may produce a clinical picture of motor- or cerebellar-like ataxia with hemisensory loss. These effects are seen contralateral to the lesion.² Lesions affecting the frontal lobe, such as tumor or cystic masses, may cause a motor ataxia of the contralateral extremities through poorly understood mechanisms.³ Nontraumatic spinal cord compression may present with gait ataxia or abnormality.⁴

SENSORY ATAXIAS

Sensory ataxias are due to failure of transmission of proprioception or position sense information to the CNS. Failure may arise from disorders affecting the peripheral nerves, spinal cord, or cerebellar input tracts. Coordinated motor performance is faulty, even though motor systems and the cerebellum are intact. Sensory ataxias may be somewhat compensated by visual sensory information. Loss of visual information leads to the observation that sensory ataxias often worsen in poor lighting conditions and may be brought out during examination.

GAIT DISORDERS

No organized classification scheme exists for gait disorders, and different authors categorize abnormal gaits in descriptive terms. A cerebellar or motor ataxic gait is widely based with unsteady and irregular steps, and compensation to barriers in the environment may be lacking. The gait of sensory ataxia resulting from loss of proprioception is noTable for abrupt movement of the legs and slapping impact of the feet with each step. A variety of other terms are used to describe abnormal gaits.

An apraxic gait is one in which the patient seemingly has lost the ability to initiate the process of walking, an “ignition failure.” This may occur with right or nondominant hemispheric lesions. Frontal lobe dysfunction may result in a similar gait and may be seen in normal pressure hydrocephalus.⁵

The term festinating gait is used to describe narrowly based miniature shuffling steps and is common in Parkinson’s disease. An abnormal gait with outward swinging or circumabduction of the leg suggests a mild hemiparesis reflecting the asymmetric weakness of the proximal lower extremity muscles. Bilateral weakness of the trunk and pelvic girdle muscles may result in a waddling gait from failure to maintain the normal position of the pelvis relative to the lower extremities.

A functional gait disorder is one in which the patient is unable to walk normally, although all motor pathways, sensory pathways, and cerebellar functions may be demonstrated to be functioning normally. The underlying problem is often a conversion disorder. Functional gaits may be bizarre, at times resembling a person balancing on a tightrope and seemingly threatening to fall but not falling. A dramatic functional gait with flailing movements without falling actually demonstrates that strength, balance, and coordination are intact.

A unifying concept defines gait disorders according to the level of processing of neurologic information (Table 169-2).^6,7 The classification scheme is not ideal but does allow a thoughtful approach to patient diagnosis.