Dear Doctors: I read your column about the scent of skin secretion changes in Parkinson's disease. A couple of years ago, I read about training canines to smell and detect lung cancer. Has there been additional work done in training canines for disease detection?

Dear Reader: Your question leads us to the fascinating and remarkable canine nose. Researchers guess that a dog's sense of smell is between 10,000 and 100,000 times more sensitive than ours. We make do with a mere 6 million scent receptors, while dogs have up to 300 million. A dog's brain also devotes about 40 times more of its real estate to decoding smell than ours does. This all adds up to a sense of smell so sensitive that it's believed a dog can detect a single molecule.

And that's where the idea of using dogs in medical diagnosis comes into play. The column you referenced explored changes that occur in the skin of people living with Parkinson's disease. These changes cause a specific scent that dogs can detect, even in minute amounts. The idea is that we could use this scent as a biomarker for early diagnosis of the disease. We are already using dogs to identify the metabolic changes that happen before an epileptic seizure. They can detect changes in blood sugar in people living with diabetes. As you point out, they can also detect certain cancers. More recently, we discovered dogs are surprisingly accurate in identifying COVID-19 infection.

All of this is possible because our bodies continually produce and release volatile organic compounds, or VOCs. These are clusters of distinct airborne molecules that humans release through sweat, breath or urine. VOCs have distinct and identifiable scents that are practically tailor-made for the nuances of the dog nose.

Although this represents a promising direction, enlisting the canine sense of smell in medical care faces some real hurdles. A big one is this requires a lot of training. First, we have to teach a dog to recognize and focus on a specific scent. Then there's an extended period of testing for reliability. Depending on the disease or condition, it can take months to a year or more for a dog to be ready to deal with patients in a clinical setting. Other considerations are stress and nose fatigue, a real phenomenon. Repeated exposure to scents can temporarily dull sensitivity.

Despite these limitations, a potential role for dogs in diagnostic medicine continues to expand. Proposed and ongoing studies are being done all over the world. There are studies for diagnosis of breast cancer through sweat samples. Research is expanding into a wider range of viral and infectious diseases. There are also efforts to combine dog research with chemical profiling to develop medical instruments based on VOC compounds. There is also encouraging news for our four-footed friends. An ongoing study is looking into a sniff test for an aggressive cancer found in dogs. Someday dogs could benefit from diagnosis by their own superpower.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: How often are multiple sclerosis (MS) and Type 1 diabetes seen in one individual? In my experience, MS specialists are not familiar with how to treat flares in people with both. I have been advised to get IV steroids to manage a flare, which would have spiked glucose. I find this lack of experience to be frightening.

Dear Reader: In explaining your situation, you have outlined one of the major challenges to crafting a treatment plan for people living with more than one autoimmune condition. This is a phenomenon known as polyautoimmunity. Some studies suggest that up to 30% of people with an autoimmune disease may develop at least one additional autoimmune condition over time. Risk factors include a family history of autoimmune disease and being female. Increased duration of the primary disease also raises the likelihood of developing another.

For those who are not familiar, an autoimmune disease occurs when the immune system mistakenly begins to target and damage the body’s own tissues. In Type 1 diabetes, certain white blood cells, including T cells, attack and destroy the insulin-producing cells in the pancreas. In multiple sclerosis, T cells and other immune cells target the protective coating around nerve fibers in the brain and spinal cord.

In autoimmune disease, a crucial state of balance has been disrupted. Known as homeostasis, this is when the body’s systems are operating properly and in harmony with one another. It is also at the heart of the dilemma doctors face when treating a person with polyautoimmunity. It often happens that a treatment used to manage a symptom, flare or complication in one disease will create an imbalance that worsens the coexisting condition.

In the case of your doctor prescribing IV steroids to manage an MS flare, they are following the standard of care. Steroids are highly effective at shutting down the inflammation associated with an MS flare. But as you point out, steroids raise blood glucose and interfere with insulin metabolism. For someone with Type 1 diabetes, this poses significant health risks. These include diabetic ketoacidosis, a potentially deadly condition. Without enough insulin, the body begins to rapidly burn fat. This produces metabolic byproducts known as ketones, which make the blood dangerously acidic.

Faced with two dangerous outcomes, the challenge for the doctor becomes finding a point of balance. They need to suppress the immune attack that is driving the MS flare without disturbing the metabolic control needed to regulate blood sugar. For treatment with IV steroids, this would require a hospital setting with stringent monitoring of ketones and electrolytes, and vigilant adjustments to insulin during and after the treatment.

All of this explains why your situation feels so precarious and, understandably, frightening. Treating two autoimmune diseases at the same time amplifies the level of care needed to stay safe. With careful planning, including coordinated care for both conditions, vigilant glucose management before MS treatment and clear guidance about warning signs, this risk can be managed.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I'm a side sleeper and normally it's on my right side. I got hurt in a soccer game, and for a couple of nights I had to switch to sleeping on my left side. Right away my heartbeat felt louder and stronger. My wife says it happens to her too and not to worry. What is going on?

Dear Reader: The phenomenon you describe is due to physiology, not pathology. That's a fancy way of saying the changes you noticed are due to how the body is structured, and not because something is wrong. To understand what is happening, why in most cases it is harmless, and what types of symptoms may require a closer look, let's begin with a bit of anatomy.

The heart sits in the center of the chest, behind the sternum. The lower tip, known as the apex, is made up largely of the left ventricle, which does most of the pumping. This part of the heart angles downward in the chest and sits slightly to the left of center. The position of the apex puts the left ventricle, which pumps oxygenated blood to the tissues of the body, close to the chest wall. When you lie on your back or your right side, the apex is not affected. But when you lie on your left side, a few things happen that can contribute to what you described.

One result of the switch in sleeping positions is the effect of gravity, which can cause the apex to move closer to the chest wall. The rib cage, which protects the heart and core organs, is somewhat flexible. The weight of the body against the mattress (gravity again) can cause a bit of compression. These contribute to the apex, and thus the strong pumping action of the left ventricle, sitting close enough to the chest wall that many people feel a perceptible thump. The stillness of the body as we drift into sleep, plus the accompanying quiet, can also amplify the physical sensations of this stronger heartbeat.

In healthy adults, sleeping position hasn’t been found to have an adverse effect on the heart or on the efficiency of its pumping action. However, there is some evidence that sleeping position can affect people living with heart arrhythmias, such as atrial fibrillation, or A-fib. This is when the heart can slip into an irregular and often rapid heart rhythm. This does not mean that sleep position causes the condition.

That said, it is important to know that certain symptoms can indicate a problem. These include persistent chest pain or pressure, particularly when it spreads to the arm, back or jaw, unusual shortness of breath, difficulty breathing, dizziness or fainting, and persistent heart arrhythmias. If these occur, it is very important to seek medical guidance right away. But without these warning signs, a louder or stronger heartbeat when sleeping on the left side is usually just a reminder of anatomy and the effects of gravity.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)