The inherited ataxias are a group of disorders characterized by incoordination and loss of balance. Many are accompanied by other neurological symptoms depending on the extent to which pathology extends beyond the cerebellar circuitry. With few exceptions, they are progressive, neurodegenerative disorders that often lead to significant debilitation and death.
Recent years have seen dramatic advances in our understanding of the genetic causes of the inherited ataxias, and with that, our ability to diagnose and classify specific genetic conditions has greatly increased.1–5 But the rapid rate of new discoveries also makes it difficult to keep abreast of the current “state of the art” in diagnosis, much less the myriad scientific advances in the field. In April 2009, a search of Online Mendelian Inheritance in Man (OMIM) at the NCBI website (http://www.ncbi.nlm.nih.gov/) returned 728 entries for the search word “ataxia.” Clearly, this massive amount of information must be prioritized to understand it. As with other recent reviews,2–4,6 here we address the primary ataxic disorders that are most clinically relevant based on their prevalence, ease of diagnosis, or response to treatment. Because this list is not exhaustive, other sources of information should be sought when necessary. Two very good online sources of frequently updated information are OMIM and Genetests (http://www.genetests.org/) a NIH funded Web site that provides information about genetic diseases including commercial and research based genetic testing. Genetests represents the single best site at which to find accurate, updated information on a wide range of hereditary ataxias.
Although there is no set clinical approach to the inherited ataxias, most specialists tend to use similar strategies when evaluating and treating someone who presents with a gait disorder that might fall into this category of disease (see Fig. 40–1). As with most clinical algorithms, the approach outlined in Fig. 40–1 represents a post-hoc conceptualization of these strategies rather than a rigid procedural prescription.
General clinical approach to the ataxic patient. GAD, glutamic acid decarboxylase.
After ensuring that the patient truly suffers from ataxia, diagnostic considerations turn to separating the inherited ataxias from acquired conditions that are potentially treatable. If there is a clear family history of the disease, an inherited cause should be suspected and then investigated after considering the inheritance pattern. Acquired causes include a number of structural, nutritional, endocrine, toxic, paraneoplastic, and inflammatory conditions, some of which can be easily identified and possibly treated (e.g., vitamin E deficiency). Of particular interest are those that are hard to distinguish from some of the inherited ataxias. Patients in this subgroup of acquired ataxia tend to have slowly developing symptoms, nonspecific magnetic resonance imaging (MRI) changes (e.g., cerebellar atrophy), and normal routine laboratory values. In this subgroup, ...