DEAR DR. ROACH: My sister broke out in a full-body rash of red, itchy blotches, and her doctor told her it was erythema multiforme. It is rare, and he sees only a few cases per year. Could you elaborate more on it — causes, treatment, etc.? — A.M.

ANSWER: Erythema multiforme is a skin condition with a characteristic rash — it looks like a target. There is a red ring with a dot in the center, which makes it different from the bull’s-eye rash that occurs in a minority of cases of Lyme disease — that ring has central clearing. The “multiforme” reminds us that the rash might appear differently in one person than another, or in the same person in different areas or over time.

EM is immune-mediated, stemming from an immune-system misfire, and is a clue to the doctor that there is something else going on. This usually is an infection — especially a herpes virus infection. There is a long list of other infections, such as mycoplasma pneumonia, viral hepatitis and salmonella, that are associated with EM. Sarcoidosis, a poorly understood, multisystem illness, is classically linked with EM, and about 10 percent of cases are drug-related, especially to anti-inflammatory drugs. In most cases, the rash disappears within two weeks, though a few people get recurrent EM.

Treatment of EM is for the underlying condition, if it’s known. Mild cases are treated with topical steroids and topical or oral antihistamines. Severe cases often are treated with oral steroids, despite a lack of definitive proof that they help. Recurrent cases require more expertise, possibly the care of a skin specialist.

DEAR DR. ROACH: A dear friend of mine has been diagnosed with diverticulitis. I understand that this condition can arise from not having enough fiber in one’s diet, yet when I serve whole grains, salads and fresh fruit, my friend says she can no longer eat these things. What can I serve my friend to help her overcome this condition? — A.

ANSWER: Most of the evidence on diverticulitis suggests that fiber reduces attacks, so I am surprised to hear that your friend has been told to avoid these foods, which tend to be high in fiber. People are frequently told to avoid foods that contain (or are) small nuts or seeds; however, there is very little evidence that these cause outbreaks of symptoms. One large study showed that people who eat more nuts and popcorn had fewer episodes of diverticulitis or diverticular bleeding. Of course, people who have had a bad response to a particular food should avoid that food, since not everyone’s body will respond in the same way.

It’s not my place or yours to try to overrule the advice your friend has been given by her doctor, who might have information that is not available to you and me. I would ask her what foods she has been recommended or that she finds are helpful.

DEAR DR. ROACH: J.E. recently asked about her elderly father-in-law and his warfarin/greens balance.

I have the same problem, and my doctor now has me using a home test unit, which my insurance covered.

As long as I remain within range for my INR, the doctor needs to see me only once every three months to test my machine (it is much like a glucometer, except that it uses slightly more blood, a drop the size of a ladybug). Perhaps this might be the way to go for J.E., as her father-in-law may feel more secure. — L.R.P.

ANSWER: Thank you for writing. I haven’t had much luck getting insurance to cover the home units, but they do make sense in some situations, especially when it is difficult to regulate the dose of warfarin or in people who live far from medical care.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from www.rbmamall.com.