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Change in timed walk as primary outcome measure of treatment response in HAMLET-P: HAM/TSP MuLticentre Efficacy trial-Prednisolone


In the absence of an internationally recognised biomarker of treatment response in HAM/TSP, the HAM/TSP clinial trial study group chose improvement of 10 meter time walk (TW) as the primary outcome measure for the HAMLET-P trial.


To define the minimum change in TW required for an observed treatment effect to be detectable and important. To calculate the sample size required for 90% power to detect this difference.


Prospectively collected TW (seconds/10m) of HAM/TSP patients from the four countries were submitted to two biostatisticians (Japan+UK). Analysis of covariance and log transformed TW were used.


Matched TW data (baseline+6 months) were available for a total of 76 patients. Mean (SD,median) TW were 23.46 (±18.9,16.32) at baseline, 24.85 (±23.89,16.38) at 6 months. Mean (SD,median) log10m TW were 2.89 (±0.72,2.79) at baseline, 2.91 (±0.74,2.80) at 6 months. The estimated SD of log10m TW after adjustment for the baseline measurement was 0.26. With 30 participants/group, we have 90% power to detect a difference of ±0.21. This corresponds to a ratio of 0.81 or 1.23, so we could detect a decrease in time of 19% or an increase of 23%. With power 80% we could detect a difference of -15% or +18%.


Prospectively collected longitudinal data on TW is useful in measuring inter- and intra- patient variability of this clinical efficacy marker. To power HAMLET-P at 90%, a minimum of 30 patients are needed in each arm, to be increased by 3-5 patients/arm to cover for 10-15% estimated trial drop-out rate.

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Correspondence to Fabiola Martin.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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Martin, F., Inoue, E., Grassi, M.F.R. et al. Change in timed walk as primary outcome measure of treatment response in HAMLET-P: HAM/TSP MuLticentre Efficacy trial-Prednisolone. Retrovirology 11 (Suppl 1), P30 (2014).

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