Clinical Features of SCA8

On the basis of clinical evaluations of over 200 patients from 25 separate families, it is apparent that SCA8 presents as a slowly progressive ataxia that largely spares brainstem and cerebral function (Koob et al. 1999; Day et al. 2000; Ikeda et al. 2000a; Juvonen et al. 2000; Silveira et al. 2000; Brusco et al. 2002; Topisirovic et al. 2002; Mosemiller et al. 2003). The disease is characterized by gait and limb ataxia, speech and oculomotor incoordination, dysarthria, and sensory loss. The onset of gait incoordination, commonly one of the initial symptoms, ranged between 13 and 60 years of age within the MN-A family, while the need for mobility aids ranged between 35 and 50 years—generally requiring at least 20 years of disease progression before an aid was needed (Day et al. 2000).

Neurological examinations commonly reveal signs of oculomotor involvement in moderate to severely affected patients (Day et al. 2000; Juvonen et al. 2000; Anderson et al. 2002). Additionally, speech is dysarthric with ataxic and spastic components for all individuals examined (Day et al. 2000). Occasionally, mild athetotic movements of extended fingers and intermittent low-amplitude myoclonic jerks in the fingers and arms are detected. An elic-itable Babinski sign is sometimes observed in severely affected individuals, whereas hyperreflexia is a common finding (Day et al. 2000; Juvonen et al. 2000). Impaired vibratory perception, indicative of mild sensory loss, was an intermittent clinical finding (Day et al. 2000).

Fig. 3 Serial MRI scans of an affected individual. Horizontal (a1, b1) and sagittal (a2, b2) MRI scans from an affected individual at ages 26 (a) and 35 (b) years. The earlier image is 9 years after onset (17 years). There is marked cerebellar atrophy, minimal brainstem atrophy, and no evidence of cerebral involvement. There is very little change over the 9-year period between scans, which is consistent with the slow progression of the disease. (Reproduced from Day et al. 2000 with permission from Lippincott Williams & Wilkins (http://ww.com))

Fig. 3 Serial MRI scans of an affected individual. Horizontal (a1, b1) and sagittal (a2, b2) MRI scans from an affected individual at ages 26 (a) and 35 (b) years. The earlier image is 9 years after onset (17 years). There is marked cerebellar atrophy, minimal brainstem atrophy, and no evidence of cerebral involvement. There is very little change over the 9-year period between scans, which is consistent with the slow progression of the disease. (Reproduced from Day et al. 2000 with permission from Lippincott Williams & Wilkins (http://ww.com))

Atrophy of the cerebellar hemispheres and vermis is apparent on MRI analysis of affected SCA8 individuals (Day et al. 2000; Ikeda et al. 2000a; Top-isirovic et al. 2002), with brainstem involvement appearing minimal. A typical SCA8 patient was tracked over a 9-year period with MRI; scans revealed little change, characteristic of the slowly progressive course of the disease (Day et al. 2000) (Fig. 3). The imaging also showed that the cerebral hemispheres, white matter, and basal ganglia were spared. In contrast, Zeman et al. (2004) reported a patient having had two MRI scans separated by 4 years—the initial scan was determined to be normal, while the second scan showed clear cerebellar atrophy.

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