Hello again, dear readers! You’ve kept our digital and postal mailboxes even more full than usual with your questions, thoughts and (thank you!) kind words. Not surprisingly, much of the discussion focused on COVID-19. To help with the volume of mail, we’ll have a separate column with your virus-related questions next week. And now, onward to the more general discussion.

-- In a column about the search for a saliva test to diagnose Parkinson’s disease, we mentioned the lack of a specific diagnostic test for the condition at this time. A reader from Oklahoma, whose wife lives with Parkinson’s disease, wondered why a test known as a DaTscan wasn’t mentioned. “It is considered reliable enough that it is often required at the start of treatment testing to prove a patient has PD,” he wrote.

DaTscan uses a radioactive isotope to assess the health of the dopamine system in the brain. It’s the loss of dopamine transporters (DaT) that leads to the neurological symptoms of Parkinson’s disease. However, the scan will return an abnormal result in any neurological condition that involves dopamine transporters. It’s used in conjunction with a neurological and physical exam to arrive at a final diagnosis, but in and of itself does not return a definitive PD diagnosis.

-- A reader from Spokane who suffers from chronic foot pain requested a copy of our column about a condition known as Morton’s neuroma. Although we can’t mail you a copy, we can provide you with the link. We hope it helps. uexpress.com/ask-the-doctors/2019/12/9/having-a-mortons-neuroma-is-a

-- In that same vein, a reader from North Carolina is disappointed that her newspaper occasionally abridges our columns. The good news is that you can find the entire (and uncut) Ask the Doctors archive at uexpress.com/ask-the-doctors.

-- A reader whose 76-year-old mother has just received a diagnosis of colon cancer wonders where to learn about clinical trials looking into the disease. An excellent resource is The National Cancer Institute, at cancer.gov. Enter the words “colon cancer clinical trial” in the search bar, and the top three results will give you a wealth of information.

-- To the reader who asked what RNA and DNA stand for, the answer is ribonucleic acid and deoxyribonucleic acid, respectively. These are the names of the sugars that serve as the backbones of the two molecules.

-- A column about hypertension led a reader to ask us to highlight something known as “white coat syndrome.” This is a condition in which someone’s blood pressure spikes in a clinical setting but is otherwise normal. Although there is no surefire cure or mitigation for this, it’s important information for your health care provider to have. They may ask you to wear a portable blood pressure monitor for 24 hours to get an accurate reading.

We’ll wrap up with another thank-you, this time to the sharp-eyed readers who pointed out an error regarding dietary guidelines for daily limits on sodium. You’re correct that the unit of measurement should have been 2,300 milligrams, and not micrograms (sigh), as we wrote.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: What can you tell me about Kawasaki disease? I read that children who had COVID-19 are getting it. But I thought children were supposedly safe from the virus. Why has that changed?

Dear Reader: You’ve broached two important topics, and we’ll take them in reverse order. As we’ve mentioned here before, every bit of information about the novel coronavirus, which we all first heard about in the final days of 2019, has been learned in real time. No one had ever seen this specific virus before, so everything about it was a mystery. This included its genetic and physical makeup, how it’s transmitted, who it affects, how it enters the body and how the body responds once an infection is launched. Our understanding of the virus and COVID-19, which is the disease that it causes, continues to evolve on a daily, and sometimes hourly, basis.

You’re correct that at the start of the pandemic, COVID-19 was known primarily as a viral pneumonia. It’s also true that doctors saw significantly fewer cases in children than among adults. People 18 and younger have accounted for only 2% of confirmed cases of COVID-19, and they often experience mild symptoms.

However, as doctors continue to treat patients, the knowledge base about the disease and its many symptoms expands. Now, emerging data points to the novel coronavirus as the cause of a potentially dangerous inflammatory condition in children. Referred to in the U.S. as multisystem inflammatory syndrome in children, or MIS-C, it involves inflammation in the heart, blood vessels, eyes and skin. Although it’s similar to Kawasaki disease, a rare inflammatory illness often seen in infants and young children, it’s not the same thing. Kawasaki disease is a condition in which high levels of inflammation affect the blood vessels that serve the heart. Untreated, it can result in damage that is life-threatening.

Symptoms of MIS-C include fever, swollen lymph nodes in the neck, a skin rash, pink eye, redness of the lips and tongue, intestinal distress, inflammation leading to poor organ function that can include the kidneys or heart, inflammation of the blood vessels and joint pain. The two most common symptoms of COVID-19 in adults, which are shortness of breath and a dry, hacking cough, often don’t show up in children. Doctors in 19 states have reported cases of the new syndrome, including hard-hit New York, New Jersey and California. The condition is also being seen in Europe and the United Kingdom.

Researchers don’t yet know what triggers the inflammatory syndrome, which is not caused directly by the novel coronavirus. However, many of the affected children are testing positive for COVID-19 antibodies. This suggests a link between MIS-C and the novel coronavirus. Some researchers suspect the syndrome is a delayed response by the immune system.

So far, the syndrome is rare, and most children are not seriously affected. However, new cases continue to emerge. This has prompted the Centers for Disease Control and Prevention to prepare a national alert with detailed information on symptoms, so that the syndrome can be quickly identified and treated.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: A friend of our family suddenly lost the vision in his left eye because of something called retinal artery occlusion. What is that? How do you protect against it?

Dear Reader: To answer your question, we should begin with a bit of anatomy. The retina is a layer of light-sensitive tissue that lines the back of the eye. Its job is to receive the incoming rays of light that pass through the lens and translate them into signals. These signals, or impulses, then travel along the optic nerve to the brain, which interprets them as the images we see. As with all tissues within the body, the retina needs a steady supply of blood to function properly. In the case of the retina, this comes primarily from an artery and a vein. If either of these vessels, or any of their smaller branches, become blocked, which is known as an occlusion, the retina sustains damage.

When a blockage occurs in the vein that serves the retina, the blood can’t drain away. Instead, it backs up and raises pressure within the eye, which can cause serious damage that affects sight. When the blockage occurs in the artery, as with your family friend, the retina is starved of oxygen and nutrients. Unless blood flow is restored quickly, the blockage will cause the cells of the retina to die. The result is a loss of vision. Unfortunately, there is no way to reverse the damage that arises as a result of retinal vessel occlusion.

One of the main causes of the condition is atherosclerosis, a disease in which fatty deposits known as plaques build up on the interior of the artery walls. These plaques can rupture and send debris into the bloodstream, which can potentially cause a full or partial blockage in another vessel. It makes sense, then, that the risk factors for atherosclerosis and for retinal vessel occlusion overlap. These include obesity, smoking, high cholesterol, high blood pressure and diabetes. Age is also a risk factor, with the majority of retinal vessel occlusions occurring in people who are 65 years of age and older. People living with a blood clotting disorder and those with glaucoma, which is chronically high pressure within the eye, are also at increased risk.

The same lifestyle changes that reduce the risk of atherosclerosis will also reduce the risk of retinal vessel occlusion, as well as diabetes, cardiovascular disease and stroke. A very important step is for smokers to quit. We know how difficult this is, so please ask your health care provider for help with crafting and sticking to a plan. Limit alcohol consumption and get regular exercise. Eat a diet that is high in fresh vegetables, leafy greens, fruits and lean meats and low in added salt, sugar and unhealthy fats. You don’t have to go for a halo here. We suggest our patients aim for 80% healthful eating. For those with health issues such as diabetes or hypertension, we tighten it up to 90% healthful eating.

Retinal vessel occlusion is a medical emergency. If you ever suddenly lose sight in one or both eyes, seek help immediately.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)