Department of Statistics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
Neuroepidemiology. 2010;34(3):163-70. doi: 10.1159/000279333. Epub 2010 Feb 2.
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.
研究罕见慢性疾病（如脊髓小脑性共济失调 3 型，SCA3）的自然病史较为困难，因为患者进入研究时的疾病持续时间不同，且随访时间间隔不规律。
我们旨在使用所有可用数据，通过马尔可夫方法描述 SCA3 长队列患者的步态共济失调进展情况。
SCA3 患者于 1998 年至 2005 年间招募，并邀请他们参加每年的神经学随访，直至 2007 年。通过平均评分图和平均轨迹图描述步态共济失调。
我们共随访了 105 例患者；基线时，平均年龄和疾病持续时间分别为 40.5（SD=12.6）岁和 7.7（SD=5.8）年。达到步态共济失调 1 期、2 期、3 期和 4 期的平均时间分别为疾病持续时间 3、5.4、10.8 和 19.4 年。平均评分图不光滑，显示出几个不太可能的起伏。平均轨迹图生成了一条连续的曲线。
马尔可夫方法描述了步态共济失调的自然病史，无需对数据进行任何事后调整，并允许对亚组进行统计比较。这种方法在未来的临床试验中对慢性退行性疾病的研究将非常有用。
