The author discusses the concept of ataxia, identifies clinical features useful in evaluating ataxic patients, and highlights the broad range of disorders that can present with ataxia as a prominent feature. He presents the differential diagnosis, treatment, and management of ataxic conditions, along with the latest information about the most recently discovered forms of hereditary ataxia.
Historical note and terminology
Ataxia is both a neurologic symptom and a sign of incoordination derived from the Greek verb tassein, meaning “to arrange” or “put in order.” Ataxic movements are poorly organized and usually relate to dysfunction of the cerebellum or its numerous connections with other brain regions (43). The Greek physician Herophilus recognized the cerebellum as a distinct brain division, but early studies of cerebellar anatomy and function were not performed until the 17th and 18th centuries (29). The first extensive clinical studies that defined cerebellar syndromes included World War I soldiers who received gunshot wounds to the head (55). Comparative studies between human and animal cerebelli helped define the function of the various cerebellar regions.
Many classification schemes have been developed for hereditary and degenerative disorders that share ataxia as a prominent presenting feature (130). Numerous new genes and their protein products have been identified over the past 15 years, and they should lead to a greater understanding of the pathophysiology and treatments for these diseases in the years ahead.
The term “olivopontocerebellar atrophy” is widely used without clear consensus on specific diagnostic or prognostic implications (10). Many cerebellar disorders were originally classified using clinical features, such as "olivopontocerebellar ataxias, types I to V," or pathological descriptions such as "spinopontine atrophy" or "cortical cerebellar degeneration" (73). These previous classification schemes built on clinical and pathological findings are being replaced by genetic classification based on identification of responsible gene mutations.
Although spasticity can be seen in several types of spinocerebellar ataxias (see Table 1), the term “spastic ataxia” is also occasionally used for the combination of spasticity and ataxia (23). The best known example of Charlevoix-Saguenay ataxia is inherited by autosomal recessive transmission due to sacsin gene (SACS/ARSACS) mutations (35). The first locus for autosomal dominant hereditary spastic ataxia (SAX1) has also been mapped (85). A case of atypical ARSACS in a Japanese patient with ataxia and polyneuropathy but no spasticity has been reported due to a novel compound mutation (p.Lys4326Glu and p.Leu1412Lysfs*16) in the SACS gene (01).