DEAR DR. ROACH: I’ve read mixed reviews as to whether the flu shot can contribute to Alzheimer’s disease. I’m anxious to see your input. — J.W.

ANSWER: There is no reliable evidence, nor any good biological plausibility, that influenza vaccination increases the risk of either Alzheimer’s disease or other types of dementia. In fact, there are several studies showing a reduced risk of dementia in people who get regular influenza vaccines. I have read well-done studies looking at people with heart failure, people with kidney disease and overall people over age 65 — all show a decreased risk of dementia among those who regularly get the vaccine.

There is a risk in these kinds of studies, because people who get regular vaccines are more likely to see their doctors, have blood pressure and blood sugar well-controlled, eat better and exercise more, all of which help protect against dementia. However, the authors did their best to statistically control for these factors and still found a benefit from regular vaccination.

One might think that reducing the risk of death by influenza vaccination would be enough motivation, but still too few people get the vaccine. Maybe knowing that there is no increased risk, and possibly a decreased risk, for dementia will encourage people to get their vaccine.

DEAR DR. ROACH: What can you tell me about hypereosinophilic syndrome? My brother is being worked up for this or a possible mutation of this disease. He has suffered for a few years with symptoms. Many doctors later, one thinks this is the diagnosis. He’s had 10 biopsies, so why did it take so long? Is it that rare? What is the treatment? — Anon.

ANSWER: Hypereosinophilic syndrome is indeed very rare, seen in perhaps 1 in a million people. Eosinophils are a type of white blood cell that are helpful for the body’s defenses, especially against parasites. In HES, however, the body makes far too many eosinophils (we often say “eos,” for short), and these can infiltrate healthy tissues, especially the lung, skin and gastrointestinal tract. As such, common symptoms are cough and shortness of breath, rash and weight loss or stomach pain. Occasionally, the disease affects the brain, eye or heart.

The diagnosis is suspected when the eosinophils in the blood are present at too high a level.

A persistent total eosinophil count over 1,500 should make the clinician suspect the diagnosis. Often eosinophils are given only as a percentage, so to get the total count, you need to multiply the percentage by the total white count. Since this is part of a complete blood count, I haven’t often seen such a long delay in making the diagnosis. One parasite, Strongyloides, can cause what looks like hypereosinophilic syndrome, so this needs to be considered before treatment.

The biopsy I think you are referring to is of the bone marrow. The bone marrow specimens should be evaluated for genetic mutations. An expert in evaluation certainly should be involved. A hematologist is usually the person who makes the diagnosis in association with the hematopathologist.

Treatment depends on the underlying genetic mutation, if present. Imatinib (Gleevec) is used for people with a mutation called PDGFRA. Steroids are used for people without genetic mutations, but must be used with caution because it can cause a fatal outcome in people with Strongyloides. People who don’t respond to steroids often receive chemotherapy or even a bone marrow transplant.

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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 send mail to 628 Virginia Dr., Orlando, FL 32803.

Dr. Roach