Chapter 20 Ataxic and Cerebellar Disorders
The term ataxia denotes a syndrome of imbalance and incoordination involving gait, limbs, and speech and usually results from a disorder of the cerebellum and/or its connections. It appears to be derived from the Greek word taxis, meaning “order” (Worth, 2004). Ataxia can also result from a disturbance of proprioceptive input due to pathology along the sensory pathways (sensory ataxia). Evidence from anatomical connectivity studies suggest not only a motor function but also a potential cognitive role for the cerebellum (Strick et al., 2009).The clinical approach to patients with ataxia involves differentiating ataxia from other sources of imbalance and incoordination, distinguishing cerebellar from sensory ataxia, and designing an evaluation based on knowledge of various causes of ataxia and cerebellar disorders (Manto, 2009; Worth, 2004). This chapter describes the clinical features of ataxia and outlines a basic approach to patients with ataxia. A more detailed description of specific disorders can be found elsewhere in this book.
Symptoms and Signs of Ataxic Disorders
A few general statements can be made regarding cerebellar diseases. Lateralized cerebellar lesions cause ipsilateral symptoms and signs, whereas generalized cerebellar lesions give rise to more symmetrical symptomatology. Acute cerebellar lesions often produce severe abnormalities early but may show remarkable recovery with time. Recovery may be less optimal when the deep cerebellar nuclei are involved (Timmann et al., 2008). Chronic progressive diseases of the cerebellum tend to cause gradually declining balance with longer lasting effects. To some extent, signs and symptoms have a relation to the location of the lesions in the cerebellum (Stoodley and Schmahmann, 2010; Timmann et al., 2008). Ataxia of stance and gait are correlated with lesions in the medial and intermediate cerebellum: oculomotor features with medial, dysarthria with intermediate, and limb ataxia with lateral cerebellar lesions (Timmann et al., 2008). Stoodley and Schmahmann (2010) also point out that such lesion/symptom correlation can be extended to the proposed cognitive and limbic aspects of cerebellar function as well with anterior lobe lesions correlating with the traditional motor abnormalities and posterior lobe lesions with cognitive changes.
Symptoms in Patients with Ataxia
Neurological Signs in Patients with Cerebellar Ataxia
Gordon Holmes (1922, 1939) is often credited with the initial description of cerebellar deficits, although earlier works had reported on the effects of cerebellar lesions. Lesions of the cerebellum can cause deficits involving gait and stance, limb incoordination, muscle tone, speech, and the oculomotor system. They may also result in subtle cognitive deficits.
Stance and Gait
Patients with cerebellar disease initially experience an increase in body sway when the feet are placed together; the trunk moves excessively in the sideways direction (lateropulsion). With more severe disease, patients experience the increased sway even with normal stance and learn that balance is better with feet apart. Healthy persons usually have a foot spread of less than 12 cm during normal stance. Patients with cerebellar disease tend to have a much larger foot spread during quiet stance (Manto, 2002). In the clinic, one can detect even subtle problems with balance by asking the patient to do a tandem stance or stand on one foot; normal adults can do these maneuvers for at least 30 seconds. The Romberg test is usually positive in patients with cerebellar ataxia, although this tends to be more prominent in patients with proprioceptive or vestibular lesions. Many patients experience rhythmic oscillations of the trunk and head known as titubation. Severe truncal ataxia can also result in inability to sit upright without back support. Gait can be tested by asking the patient to walk naturally down a straight path. Ataxic gait is characterized by a widened base and an irregular staggering appearance resembling alcoholic intoxication. Overall, the speed of movements is not severely impaired, though patients may deliberately slow down to keep their balance. The steps are irregular, and the patient may lurch in unpredictable ways. Ataxic gait disturbance can be detected even earlier by testing tandem gait; patients with cerebellar lesions lose their ability to do heel-to-toe walking in a straight line.
Abnormalities of Muscle Tone and Strength
Although hypotonia can occur in acute cerebellar disease, it is not a major feature of most cerebellar diseases. The inability of patients to check forearm movement in the rebound test is often said to result from hypotonia but may have other explanations. Similarly, cerebellar lesions do not cause loss of strength in the traditional sense, but many patients experience problems with sustaining a steady force during sustained hand use (isometrataxia) (Manto, 2002).
