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Graves’ Ophthalmopathy^a

Department of Endocrinology and Internal Medicine Herlev Hospital DK 2730 Herlev, Denmark

To the editor:

The fact that Kahaly et al. (1) apparently ignore patients lost to follow-up may have lead them to draw false conclusions.

They report recovery in 12 of 18 patients with Graves’ ophthalmopathy treated with orbital radiotherapy in 20 divided fractions of 1 Gray (Gy) over 20 weeks (group A). This success rate of 67% was, according to the authors, significantly higher than the rates of 59% and 55% obtained with treatment regimens of 1 and 2 Gy in 10 fractions over 2 weeks (groups B and C). The authors subsequently conclude that the 1 Gy/week regimen was the most effective.

One thing is that it seems quite implausible that the difference between a success rate of 67% (12 of 18) compared with a success rate of 55% (12 of 22) could reach P equal to 0.007 as reported. In a ² test the finding is clearly insignificant (P > 0.5). But, we comment also on another major problem in the data handling.

As reported by the authors, three patients were excluded before the statistical analysis "because of insufficient follow-up and poor compliance" of whom all were originally randomized to group A. This is not subject to further discussion in the paper, but it seems certainly not unlikely that the drop-outs could have represented treatment failures because compliance with the 20-week treatment protocol must have been difficult to assertain if no progress was noted by the patient. In an intention-to-treat perspective the recovery rate in group A should, therefore, have been calculated as 12 of 21 corresponding to 57%. This obviously wrecks any attempt to claim superiority of the 20-week protocol.

Footnotes

^a Received November 12, 2000. Address correspondence to: Dr. Erik Christiansen, Department of Endocrinology and Internal Medicine, Herlev Hospital, DK-2730 Herlev, Denmark.

References

1. Kahaly GJ, Rösler HP, Pitz S, Hommel G. 2000 Low versus high-dose radiotherapy for Graves’ ophthalmopathy: a randomized single blind trial. J Clin Endocrinol Metab. 85:102–108.[Abstract/Free Full Text]

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