94 Meridian Ave. Haileybury, Ont. Occult blood screening. I compliment Dr. Simon on his excellent review of the pros and cons of screening for fecal occult blood ...
bers of the hospital board to a centre where conferences on these topics might be held. On many occasions warm personal relationships have been established with consultants in Toronto, and some have visited our hospital. For example, after the journal club's meeting on palliative care the resource person came to our hospital, and later a palliative care unit was established here. In addition, two department heads from the Toronto General Hospital whom we first met through the journal club are now travelling to our hospital every 3 months to hold patient clinics. Although New Liskeard is 530 km north of Toronto, the Telemedicine Bridge has in many ways allowed us to insinuate ourselves into the heart of academic
medicine. Hartley F. Jeffery, MD, FRCS, FRCSC 94 Meridian Ave. Haileybury, Ont.
Occult blood screening I compliment Dr. Simon on his excellent review of the pros and cons of screening for fecal occult blood (Can Med Assoc J 1985; 133: 647-649). As the public becomes more educated it will demand, and deserve, sound scientific recommendations based on rational, rather than emotional, assessments. The American Cancer Society recommends that testing of stool for occult blood be done not as a solitary procedure but as a portion of a triad that also includes regular rectal examination and proctosigmoidoscopy. This regimen points to the only likely solution. Prevention is indeed the best way to reduce the incidence of cancer of the colon, which afflicts more than 10 000 Canadians annually. Most international epidemiologists, the National Cancer Institute of Canada, and the Canadian and American cancer societies have agreed that adopting a 1200
diet that is high in fibre, low in fat (less than 30% of the total energy intake consisting of fats) and rich in vitamins A and C will likely decrease the risk of cancer of the colon and breast and possibly decrease that of cancer of the prostate, uterus and ovary. As the controversy over appropriate screening continues we must not lose sight of primary prevention as our most powerful tool. Geoffrey Davis, MD Chairman Medical Advisory Committee Canadian Cancer Society Ontario Division Toronto, Ont.
Simon's article on occult blood screening is a good evaluation of an important problem. However, I disagree with the statement that a positive result of Hemoccult screening necessitates sigmoidoscopy.
Sigmoidoscopy, with a rigid or (preferably) flexible instrument, is an integral part of a program of screening for colorectal cancer.'2 Many physicians appear to have abandoned this unpleasant examination as a screening test in preference to relying entirely on occult blood testing.3'4 The relatively high false-negative rate (low sensitivity) of the Hemoccult II test, particularly in the rectosigmoid, suggests that using this test alone is not an adequate screening program.5'6 Studies have shown that routine sigmoidoscopy with a rigid instrument detects colorectal cancers and that routine removal of adenomas decreases the incidence of subsequent cancer;7'8 however, prospective randomized controlled studies are needed to confirm these findings. Nevertheless, Simon is probably correct in stating that as of now there is no evidence that a nation-wide occult blood screening program among asymptomatic patients would decrease the mortality of colorectal cancer or be "cost-effective". However, the practising clinician is often faced with a healthy patient who presents for a routine examination and wants reassurance that he or
CAN MED ASSOC J, VOL. 133, DECEMBER 15,1985
she does not have this common malignant disease. This situation is often described as case finding, as opposed to mass population screening. President Reagan's recent surgery for cancer of the colon has likely heightened public awareness of this disease. The frequent presence of nonspecific gastrointestinal symptoms in patients without cancer compounds the problem.9 Routine bariumenema roentgenography and colonoscopy would definitely rule out malignant disease, but at enormous cost and not without morbidity and even mortality. Therefore, in clinical practice the physician should follow the guidelines of the American Cancer Society for detecting colorectal cancer.2 These include history-taking and physical examination to identify patients who are at increased risk or who have symptoms that are strongly suggestive of colorectal cancer; for asymptomatic persons at normal risk the society recommends occult blood testing once a year and proctosigmoidoscopy every 3 to 5 years beginning between the ages of 40 and 50. Although this approach represents a compromise between overinvestigation and doing nothing, in a nonperfect world it seems to be the best clinical strategy for a common and serious disease. Martin H. Poleski, MD, FRCPC
Department of Medicine Division of Gastroenterology Sir Mortimer B. Davis Jewish General Hospital Montreal, PQ
References 1. Winawer SJ, Poleski MH, Sherlock P: Susceptibility to colorectal cancer: current concepts of screening, diagnosis and risk. In Berk JE (ed): Developments in Digestive Diseases, vol 2, Lea & Febiger, Philadelphia, 1979: 73-87 2. American Cancer Society: Cancer of the colon and rectum: a summary of a public attitude survey. CA 1983; 33: 31-37 3. Cummings KM, Jaen CR, Funch DP:
Family physicians' beliefs about screening for colorectal cancer using the stool guaiac slide test. Public Health Re.p 1984; 99: 307-312.
4. American Cancer Society: Survey of physicians' attitudes and practices in early cancer detection. CA 1985; 35:
of fecal blood testing for the detection of colorectal neoplasia. Cancer 1980; 45: 2959-2964
197-213
5. Poleski MH, Gordon PH: An estimate of the sensitivity of Hemoccult IT® slide test in detection of colonic neoplasms [abstri. Ann R Coll Physicians Surg Can 1983; 16: 329 6. Winawer SJ, Andrews M, Flehinger B et al: Progress report on controlled trial of fecal occult blood testing for the detection of colorectal neoplasia. Cancer 1980; 45: 2959-2964
7. Hertz RE, Deddish MR, Day E: Value of periodic examination in detecting cancer of the rectum and colon. Postgrad Med 1960; 27: 290-294 8. Gilbertsen VA: Proctoscopy and polypectomy in reducing the incidence of rectal cancer. Cancer 1974; 34: 936-939 9. Drossman DA: Diagnosis of the irritable bowel syndrome. A simple solution? Gastroenterology 1984; 87: 224225
[Dr. Simon replies:]
My paper was confined to occult blood surveillance and therefore did not discuss sigmoidoscopy. Certainly I agree with Poleski that the latter is often crucial and cannot be replaced by occult blood testing. In the Sloan-Kettering study, for example, one quarter of the cancers and three quarters of the polyps seen by sigmoidoscopy were overlooked by occult blood testing.' Direct visualization of the rectosigmoid is essential in symptomatic patients and is desirable for screening high-risk individuals. It does not necessarily follow, however, that routine surveillance sigmoidoscopy is warranted in asymptomatic persons at "normal" risk. Like the question of occult blood testing, this issue is complex and has both pros and cons. The arguments cannot be analysed here, but a reasonable conclusion can be reached either way. Jerome B. Simon, MD, FRCPC Associate professor of medicine Queen's University Kingston, Ont.
Reference 1. Winawer SJ, Andrews M, Flehinger B et al: Progress report on controlled trial
Hypotension during urography in patients taking f-blockers D_ rs. Skidmore and Langlois (Can Med Assoc J 1985; 133: 724-726) rightly take exception to the comment in my article (ibid: 122) that 3blockers "suppress" catecholamine production. I had meant to say "depress". I agree that fblockers act primarily on fiadrenergic receptor sites, but, as Langlois notes, "some observations suggest that :-blockers act on presynaptic d-receptors to reduce the amount of norepinephrine liberated by each nerve impulse". Since epinephrine is produced by the' action of phenylethanolamine -N- methyltransferase on norepinephrine,' such fblocker activity would depress the production of both norepinephrine and epinephrine. In denying that I related fiblocker therapy to the hypotensive crises I encountered, Skidmore ignores my reference to the known hypotensive action of contrast agents used for intravenous pyelography.23 Adding to this the known direct cellular action of contrast agents (particularly meglumine-containing compounds) that causes leukocytic histamine release3 and the fact that patients can have pronounced idiosyncratic reactions to any drug, one can see how a severe hypotensive reaction could occur when a significant part of the sympathetic nervous system has been severely depressed by f-blockade. In addition, propranolol, the keystone of fiblocker therapy, is one of the drugs that liberate histamine by direct action on mast cells and leukocytes.4 This emphasizes the contraindication of fl-blocker therapy in patients with asthma in whom bronchodilation by fi-
adrenergic agents is blocked and who overreact to histamine. Langlois's proposal that the tachycardia and the loss of the radial pulse in case 2 may have been related to adrenal medullary release of large quantities of norepinephrine and to the effects of peripheral vasoconstriction does not equate with clinical experience. In my clinical years, 1955 to 1966, when the Levophed (levarterenol [norepinephrine] bitartrate) drip was in vogue, so pronounced was the peripheral vasoconstriction that gangrene of the fingers or toes occurred in some cases, and full-thickness skin necrosis developed when the infusion became interstitial, yet the pulse remained bounding at the wrist - unless shock existed. If my reasoning is correct in linking severe hypotensive reactions to f-blocker therapy and histamine release by contrast agents, then Skidmore may be dealing with a similar situation when he encounters the protracted severe hypotensive reaction that the Compendium of Pharmaceuticals and Specialties (CPS) cites as occurring occasionally during general anesthesia in patients receiving fl-blocker therapy,5 since d-tubocurarine, a muscle-relaxing drug commonly used in anesthesia, is so potent in its ability to cause histamine release by direct cellular action that it has been used as a laboratory standard since 1936.3,6 In the treatment of hypotension occurring in a patient receiving f-blocker therapy one is confronted with a paradox: a fiadrenergic agonist should be best; however, from a review of all of the fl-blocking agents listed in the 1985 CPS the drug of choice appears to be epinephrine, since it is recommended in each monograph as the agent of choice when hypotension appears as a result of fl-blocker overdose.5 Skidmore and Langlois question the lack of blood pressure measurements in my two case reports. I invariably monitor the pulse for 3 to 5 minutes just before and after the injection (and during the injection if it is done slowly) and continue the
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