A Prospective Study of SCA3 Gait Ataxia Described through a Markovian Method

Studies on the natural history of rare, chronic diseases like spinocerebellar ataxia 3 (SCA3) are hard to be done, since patients enter the study with variable disease durations and are followed up at irregular intervals.Our purpose was to use all the available data to describe the progression of gait ataxia in a long-term cohort of patients with SCA3 through a markovian method.SCA3 patients were recruited between 1998 and 2005 and were invited to annual neurological follow-ups until 2007. Gait ataxia was described through a mean score graph and a mean trajectory graph.We followed up 105 patients; at baseline, the mean age and disease duration were, 40.5 (SD = 12.6) and 7.7 (SD = 5.8) years, respectively. The mean time to reach stages 1, 2, 3 and 4 of gait ataxia were 3, 5.4, 10.8 and 19.4 years of disease duration. The mean score graph was unsmooth, showing several unlikely ups and downs. The mean trajectory graph produced a continuous curve.The markovian method described the natural history of gait ataxia without any a posteriori adjustment of data and allowed statistical comparisons between subgroups. This method will be useful in future clinical trials in this and in other chronic degenerative diseases.