Doctor Decoded: Disease vs. Syndrome

Irritable bowel syndrome. Chronic fatigue syndrome. Fibromyalgia syndrome. Dry eye syndrome. Sudden infant death syndrome. Metabolic syndrome. These are just a handful of common syndromes that afflict humans, but it's likely that you've never stopped to think about what the word actually means. (And no, syndrome isn’t just a fancy synonym for disease.)

Disease usually refers to a health problem with a known cause that tends to affect a specific part or system of the body, and it produces noticeable symptoms. Diseases also tend to produce damage or changes that show up in tests (such as blood, urine, or saliva tests) or imaging (such as X-rays or MRIs).

Examples of diseases include heart disease, diabetes, and cancers, as well as autoimmune diseases like rheumatoid arthritis and psoriasis. Medical researchers know how these diseases develop, and they have specific medical tests to help diagnose them. For example, doctors can use various blood sugar tests to diagnose diabetes, and rheumatoid arthritis can cause physical changes to the joints over time that can be seen on an X-ray.

By contrast, syndrome usually refers to a collection of related symptoms, often without a clear cause (there are some exceptions, but more on that later). Syndromes don’t typically cause damage to certain organs or body systems, and they may not create changes that show up in blood tests or X-rays, for example. Medical tests for someone with a syndrome might show that things are more or less "normal."

As a result, many syndromes are difficult to diagnose, and doctors usually have to use process of elimination to rule out other diseases. Treatment for syndromes are also a challenge. When researchers don’t know what’s causing a health condition, they often don’t know how to treat it precisely and effectively.

The most famous example is irritable bowel syndrome (IBS), which produces digestive distress without any proven cause or visible damage to the colon. That’s a stark difference to other gastrointestinal diseases like Crohn’s or ulcerative colitis, which reveal inflammation and damage in the digestive tract during a colonoscopy.

The stigma against syndromes

It’s a myth that syndromes are “all in your head,” or that they’re not serious. Many patients with syndromes often have to be strong self-advocates about the symptoms they are experiencing and how they are affecting their lives in order for loved ones—or even doctors—to take them seriously.

For example, IBS is one of the greatest causes of work absenteeism. In a 2018 study from American Journal of Gastroenterology, about 25 percent of surveyed IBS patients reported missing work because of IBS symptoms, and close to 90% reported “presenteeism,” i.e., when you show up to work sick but are not fully functional.

Similarly, people with fibromyalgia — which causes chronic and widespread pain without clear cause — may struggle with others who think they are “being dramatic” or even making it up. They may feel constant pressure to defend themselves to loved ones, and they’re more likely than the average person to experience depression.

In reality, the word syndrome just implies that researchers and doctors don’t fully understand them yet. In fact, many former syndromes have been renamed as diseases once a cause was identified.

Clear definitions, messy naming

While definitions for disease and syndrome do exist, the naming of conditions do not always fit in practice. Some syndromes, like polycystic ovary syndrome and sweet syndrome continue to be syndromes even after a cause is identified. Down syndrome, for example, now has a known genetic cause, but it continues to be known as a syndrome.

Then there’s Lyme disease, which is an accurate name for the infection caused by the Borrelia burgdorferi bacterium spread by ticks. However, it gets trickier when people refer to “chronic Lyme disease,” which is when symptoms of Lyme disease persist long after antibiotic treatment.

Because researchers don’t know why this occurs in a small group of Lyme patients, they prefer to call this phenomenon “post-treatment Lyme disease syndrome.” Due to the stigma against syndromes, this has resulted in some conflict as patients believe researchers are doubting or downplaying their experience.

If you suffer from syndromes like IBS or fibromyalgia, the good news is that research is always ongoing, and experts discover new clues about even the most mysterious syndromes all the time. Today’s syndromes may soon be tomorrow’s treatable diseases.