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Am Fam Physician. 2000;62(3):658

Tuberculin Testing

(Hong Kong—The Hong Kong Practitioner, March 2000, p. 116.) Derived from Mycobacterium tuberculosis, purified protein derivative (PPD) used with correct Mantoux technique can provide the most accurate and reliable skin test for evidence of exposure to tuberculosis. Worldwide, several preparations and strengths of PPD are available. Physicians should verify the type of preparation used when interpreting test results in patients from overseas. Mantoux results depend on the widest diameter of induration at 48 to 72 hours after intradermal injection of PPD. The “Sokal ballpoint pen method” uses resistance to the pen's movement across the skin to determine the diameter of induration. A line is drawn with a “medium” ballpoint pen from a point 1 to 2 cm from the margin of the skin-test reaction toward its center. This simple technique can significantly reduce interobserver variability in reading the test results. A positive test may indicate previous exposure to mycobacteria other than M. tuberculosis. False-negative results may be caused by faulty technique in administering or reading the test or improper storage of PPD. Patient-related factors that may lead to false-negative tests include acute infection with another illness, recent immunization with live virus and conditions such as lymphoma.

Placebos and Placebo Effect

(Hong Kong—The Hong Kong Practitioner, March 2000, p. 123.) Although pharmacologically inert, placebos are reported to benefit more than one third of patients who use them. Like a physician's enthusiasm or pleasant demeanor, placebo effects are not technically components of treatment. However, they are integral to treatment. Placebo-induced relief of symptoms has been reported for a wide range of conditions, but for any given condition relief ranges from zero to 100 percent. Placebos have been most widely used and studied in pain relief. Gender, intelligence and degree of suggestibility do not seem to influence a patient's responsiveness to placebos; however, mildly depressed patients react better to placebo than do patients with severe depression.

When physician-patient relationships are strongly positive, the placebo effect can be enhanced. Placebos may be linked to adverse effects in about one third of recipients and may have directly adverse effects if they undermine the physician-patient relationship. Overall, there is much to learn about placebo substances and the placebo effect. In the interim, physicians are cautioned to use placebos discreetly when they are “likely to elicit a healing process from within the patient.”

The Odors of Flatus

(Britain—The Practitioner, April 2000, p. 301.) Although flatus has been a social and, possibly, a medical challenge since antiquity, research into flatus was stimulated by concerns that astronauts could suffocate or produce explosive gases during space missions. Normal persons pass flatus up to 20 times per day; men are reported to pass flatus twice as often as women do. More than 99 percent of colonic gas is an odor-free mixture of oxygen, carbon dioxide, nitrogen, hydrogen and methane. Offensive odors of flatus are attributed to trace amounts of volatile gases, particularly those containing sulfur, that can be detected in a few parts per million. These volatile gases result from bacterial action on sulphates in foods such as cruciferous vegetables (e.g., broccoli, cabbage, cauliflower), bread, beer, and methionine or cysteine-containing proteins. For most patients, adjustment of diet is sufficient. While studies have found that treatment with oral charcoal is ineffective, it is used by many patients. Use of undergarments with charcoal-impregnated cushions had an 11-fold reduction in the sulfur-containing component of escaping intestinal gas.

Allergy to Peanuts

(Britain—The Practitioner, April 2000, p. 352.) Peanuts are the most common cause of food-associated anaphylaxis and death in Britain. Peanut allergy affects approximately 1 percent of British preschool children and the incidence of peanut allergy has doubled in the past decade. Patients with peanut allergy frequently have atopic conditions and/or asthma and may also be allergic to other foods, especially tree nuts. The initial allergic reaction may be severe and can occur following the first known exposure to peanuts, which suggests sensitization in-utero or via breast-feeding. Skin-testing and assessment of specific immunoglobulin E in serum can confirm the diagnosis. Food challenges may be extremely dangerous and should only be performed in extreme circumstances and with resuscitation facilities available. The management of peanut allergy depends on awareness and avoidance of potential exposure. Self-injectable adrenaline rescue therapy may be managed by many children and families.

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