Ataxia and Gait Disorders


8	Ataxia and Gait Disorders

The staggering steps of a young child learning to walk are a classic example of ataxia, a condition in which the control of motor movements is impaired in the absence of muscle weakness. The term ataxia is of Greek origin, with “a taxis” meaning “without order or arrangement.” The precision of movement is controlled by an intricate sensory and motor feedback system, with key processing of this information occurring in the cerebellum. As such, disorders affecting the modulation of information entering or leaving the cerebellum may affect the specific components of movement including rate, direction, force, and rhythm. Depending on the pathologic cause, ataxia can be diffuse, unilateral, or bilateral. It can affect the upper limb, lower limb, and truncal, ocular, or bulbar muscles. Although ataxia can cause significant difficulties with walking, it is not the only type of gait abnormality. This chapter will review common causes of ataxia and gait disorders.

ATAXIA

DIAGNOSTIC APPROACH

Ataxia is not a diagnosis, but rather a neurologic examination finding. There are many ways in which ataxia may manifest clinically. Patients may complain of clumsiness, gait difficulties, speech or swallowing difficulties, or other problems. Because of the diverse array of symptoms, several terms are used to describe specific aspects of ataxic movements. They include the following:

1.Dysarthria: speech characterized by poor articulation. Although not specific for ataxic disorders, ataxic disorders can lead to slurred, slow, hesitating, and effortful speech.

2.Dysmetria: incoordination of movement characterized by under- or overshooting the intended position of the limb or eyes. Dysmetric movements appear jerky and erratic.

3.Dysdiadochokinesia: impaired ability to perform movements that require a rapid change of motion, leading to an inability to keep a steady rate or rhythm.

4.Gait ataxia: broad-based and staggering steps because of incoordination of the legs.

5.Intention tremor: a tremor with an increasing amplitude at the end of a voluntary movement, due to impaired control of the proximal limb muscles.

6.Nystagmus: periodic, rhythmic oscillation of the eyes. Nystagmus can vary significantly based on the underlying cause. It can be present in primary gaze or in specific directions of gaze.

7.Truncal ataxia: instability of the truncal muscles, often manifested by oscillatory movements of the trunk when sitting or standing.

8.Pseudoathetosis: involuntary, slow, writhing movements of the digits or distal limbs when the eyes are closed; this results from loss of proprioception.

Given the number of disorders that cause ataxia, the presence and distribution (focal, diffuse, unilateral, etc.) of the physical examination findings are key to making a clinical diagnosis. These findings, however, remain tied to the patient’s history. By understanding the nature of the ataxia (temporary, progressive, or episodic), the acuity and age of onset, and family history, the differential diagnosis can be pared down significantly.

ATAXIC DISORDERS

Ataxia is a hallmark of cerebellar disease. As there are many disorders that affect the cerebellum, it is often the nonataxia-associated symptoms and examination findings that help differentiate the origin of the ataxia (Table 8-1). Similarly, the time course of symptom onset and progression aids substantially in diagnosis. Differentiated by time course, several common causes of ataxia are summarized here and in Box 8-1.

TABLE 8-1. Associated Symptoms and Signs in Cerebellar Ataxia
Associated Symptom or Sign	Diagnostic Possibilities
Vomiting	Cerebellar stroke, posterior fossa mass
Fever	Viral cerebellitis, infection, abscess
Malnutrition	Alcoholic cerebellar degeneration, vitamin E deficiency
Depressed consciousness	Cerebellar stroke, childhood metabolic disorders
Dementia	Creutzfeldt–Jakob disease, inherited SCA
Optic neuritis	Multiple sclerosis
Ophthalmoplegia	Wernicke encephalopathy, MFS, multiple sclerosis, cerebellar stroke, posterior fossa mass
Extrapyramidal signs	Wilson disease, Creutzfeldt–Jakob disease, olivopontocerebellar atrophy
Hyporeflexia or areflexia	MFS, Friedreich ataxia, alcoholic cerebellar degeneration, hypothyroidism
Downbeat nystagmus	Foramen magnum lesion, posterior fossa mass
MFS, Miller Fisher syndrome; SCA, spinocerebellar ataxia.

ACUTE ONSET ATAXIA

Cerebellar strokes, either with infarction or hemorrhage, typically present as acute onset ataxia. Depending on where in the cerebellum the infarct has occurred, clinical symptoms may include truncal ataxia (seen with lesions of the cerebellar vermis) or ipsilateral limb ataxia (with cerebellar hemisphere lesions). In many cases, there is associated vomiting, vertigo, nystagmus, and dysarthria. In cases where hemorrhage or postinfarction swelling leads to compression of the brainstem, impaired levels of consciousness may occur. Because of this potential complication, cerebellar strokes are considered medical emergencies.

BOX 8-1. Differential Diagnosis of Ataxias

Acute or subacute onset

Cerebellar hemorrhage or infarction

Postinfectious or infectious cerebellitis

Toxic (phenytoin, barbiturates, alcohol)

Multiple sclerosis

Episodic ataxia

Acute or subacute with progressive course

Paraneoplastic cerebellar degeneration

Alcoholic or nutritional degeneration

Posterior fossa mass

Chronic onset and progressive course