Correspondence that it is therefore eminently possible to tailor screening protocols to suit individual needs. Third, it is stated that individuals with a family history of colorectal cancer have a propensity to develop right-sided lesions. Although this is the case for hereditary non-polyposis colorectal cancer, there is no evidence that it is so for those with a familial tendency. Finally, he points out that it is inappropriate to carry out an incomplete examination on screened patients and thereby perhaps give false reassurance. We would agree with this general sentiment but must point out that he has partly based his viewpoint on a study that found no more pathology in these people than in the general population3. Colonoscopy is an investigation with a morbidity and mortality rate. We believe that the evidence to advocate a ‘blanket’ policy of colonoscopy for all levels of family risk has not been shown by the currently available data. L. Hunt N. C. Armitage

should be noted that, when a patient who has a positive family history of colorectal cancer is being screened by sigmoidoscopy alone, the data suggest that if they do actually have a tumour in the colon or rectum there is only a 50-60 per cent chance of detecting it.

M. G. Dunlop Medical Research Council Humun Genelics Unit Western General Hospital Edinburgh EH4 2XU UK

I.

2.

McConnell JC, Nizen JS, Slade MS. Colonoscopy in patients with a family history of colon cancer. Dis Colon Recium 1990; 33: 105-7. Herrera L, Hanna S. Petrelli N, Nava H. Screening endoscopy in patients with a family history positive ( F H f ) for colorectal neoplasia (CRN). Gastrointest Endosc 1990; 36: 21 1 (Abstract).

Department of Surgery University Hospital Queen’s Medical Centre Nottingham NG7 2UH UK 1.

2. 3. 4.

McConnell JC, Nizen JS, Slade MS. Colonoscopy in patients with a family history of colon cancer. Dis Colon Rectum 1990; 33: 105-7. McConnell JC. Colonoscopy or flexible proctosigmoidoscopy. Dis Colon Rectum 1990; 33: 722. Grossman S, Milos ML. Colonoscopic screening of persons with suspected risk factors for colorectal cancer. I : Family history. Gastroenterology 1988; 94: 395-400. Herrera L, Hanna S, Petrelli N, Nava H. Screening endoscopy in patients with a family history positive ( F H + ) for colorectal neoplasia (CRN). Gastrointesf Endosc 1990; 36: 211 (Abstract).

Author‘s reply Sir Miss Hunt and Mr Armitage fail to note that the paper by McConnell et al.’ reported data on 125 individuals who were negative on faecal occult blood (FOB) testing and had no prior history of colorectal neoplasms. A total of 106 individuals were excluded who had a positive family history but were FOB-positive and/or who had a prior history of neoplasms, because they stated that colonoscopy would be required in these anyway. The comment that 95 per cent of this group underwent unnecessary colonoscopy is countered by the fact that this was a highly selected cohort. was The suggestion that inference from the data of Herrera et guesswork seems somewhat harsh. Nineteen of the original 200 patients with a positive family history were found to have polyps on flexible sigmoidoscopy. All 181 patients negative on flexible sigmoidoscopy were invited for colonoscopy and 70 accepted. Seven (10 per cent) had neoplasia, one with cancer. Even if none of the remaining 11 1 patients who declined colonoscopy had proximal neoplasia, the sensitivity of flexible sigmoidoscopy in the total study group was 73 per cent but missed the only cancer in the study group. However, I stand by the inferred data since there is no reason to suspect a systematic bias in individuals accepting colonoscopy. The inferred prevalence of neoplasia detectable only by colonoscopy in the 181 patients who were negative on flexible sigmoidoscopy was 21 per cent. This is simply an extrapolation from the 70 actually examined. Since any screening of first-degree relatives of affected individuals will be, by definition, prospective, it will not be known which of the families are actually hereditary non-polyposis colorectal cancer families, and so the comments on right-sided propensity are to some extent irrelevant. I agree with Hunt and Armitage that many of the published studies either do not mention polyp size or include smaller polyps in the analysis. We do not know the importance of such lesions when a family history of colorectal cancer is present. However, the combination of results from studies cited in this review includes small and large polyps detected by flexible sigmoidoscopy or colonoscopy, and so the comparison of detection rate is valid. Clearly there is morbidity and mortality associated with any invasive procedure such as colonoscopy, but this must be balanced against the need to do anything at all. It

Br. J. Surg., Vol. 79, No. 12, December1992

Mechanism of action of external compression on venous function Sir We read with interest the paper by Sarin and colleagues (Br J Surg 1992; 79: 499-502) that examined venous reflux in 57 limbs while a pressure cuff was inflated around the knee. The authors demonstrated that in 15 limbs venous competence was restored before complete venous occlusion, concluding that compression therapy acts by restoring competence to dilated incompetent valves. However, a pressure of 40 mmHg at the knee restored venous competence to only five of the 57 limbs (9 per cent). Since most compression stockings exert this pressure or less at the ankle, reducing towards the knee, this surely suggests that such stockings do not act by restoring valvular Competence. We have studied venous reflux in 22 incompetent major calf veins of 19 limbs by duplex ultrasonography with and without grade 2 compression stockings. We found that the compression stockings reduced peak reflux velocity and venous diameter, but restored competence in only two veins (9 per cent): one restored to complete competence and in one the duration of reflux was reduced to ~ 0 . s.5 In our opinion these studies both suggest that compression hosiery does not act by restoring competence to dilated incompetent venous valves.

S. P. K. Payne N. J. M. London C. J. Newland W. W. B a d e P. R. F. Bell Department of Surgery Clinical Sciences Building Leicester Royal Injirmary PO Box 65 Leicester LE2 7LX UK

Authors’ reply Sir Mr Payne and colleagues are entirely correct in expressing concern that compression hosiery may not act by restoring competence to valves in large veins. We are grateful to them for presenting data that cover an issue not addressed in our original paper, i.e. the effect of applying compression hosiery to the competence of large-sized veins. In our study we deliberately avoided compressing the limb distal to the level of the hydraulic cuff so as to separate the local effect of compression from that of total limb compression, making direct comparison between our cuff and hosiery difficult. We demonstrated that at an external compression pressure of 40mmHg, only 9 per cent of veins were restored to competence and that at a higher pressure up to 27 per cent regained competence. Although the pressure exerted by hosiery at the ankle at rest is

Mechanism of action of external compression on venous function.

Correspondence that it is therefore eminently possible to tailor screening protocols to suit individual needs. Third, it is stated that individuals wi...
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