Radiography as primary outcome in RA: sample sizes for trials with 3 months follow- up

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Ann Rheum Dis. 2004 Mar 22 [Epub ahead of print]

Radiography as primary outcome in rheumatoid arthritis: acceptable

sample sizes for trials with 3 months follow- up.

Bruynesteyn K, Landewe R, Van Der Linden S, Van Der Heijde D.

University Hospital Maastricht & Caphri Research Institute, Maatsricht,

the Netherlands.

OBJECTIVES: To investigate whether plain radiographs are able to reveal

changes in joint damage due to Rheumatoid Arthritis within a 3-month

interval. METHODS: One-hundred-and-eighty-eight film pairs taken with a

3-month interval were evaluated. They were scored with (chronological)

and without (paired) knowledge of the sequence of the films according to

the Sharp/van der Heijde method. Changes in joint damage were analysed

on a group and on an individual level for different subsets of patients.

Sample sizes required to detect statistically and clinically significant

differences were estimated based on the percentages of patients with

progression larger than the smallest detectable change (SDC). RESULTS:

Changes in joint damage were seen by both the chronological and the

paired scoring method. The percentage of patients with progression of

joint damage larger than the corresponding SDCs (1.7 and 2.4) varied in

the subsets from 18% to 64% if based on the chronological change-scores

and from 9% to 36% using paired change-scores. Acceptable sample size

estimates were seen in several subsets, depending 1) on how the

investigated drug would reduce the individual risk on progression of

joint damage (by an absolute or a relative risk reduction model), 2) on

how damage was scored (chronological or paired), 3) on the baseline risk

and 4) whether 2 sided or 1-sided test would be used.

CONCLUSIONS: It is possible to reliably detect changes in joint damage

due to RA already within 3 months. This finding can be used to plan

short- term randomised controlled trials with radiographic progression

as primary outcome.

PMID: 15037445

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