Doctors are becoming better at diagnosing metastatic carcinoid tumors (MCTs). However, the varied symptoms of an MCT can sometimes lead to misdiagnosis and incorrect treatment, until a carcinoid tumor is revealed to be behind those symptoms. According to the National Organization for Rare Disorders, carcinoid tumors are often initially misdiagnosed as irritable bowel syndrome (IBS) or Crohn’s disease, or as a symptom of menopause in women.

Knowing the differences between the symptoms of carcinoid syndrome and IBS can give you an idea which condition you might have, and what you should ask your doctor to find out for sure.

According to the journal American Family Physician, most carcinoid tumors don’t cause symptoms. Often, a surgeon discovers one of these tumors while performing surgery for another issue, such as acute pancreatitis, blockage of a person’s bowel, or diseases involving a woman’s reproductive tract.

Carcinoid tumors can secrete a number of hormones that affect your body, the most significant being serotonin. Increased serotonin in your body can stimulate your bowel, causing IBS-like symptoms, especially diarrhea. Other symptoms associated with MCTs include:

  • flushing
  • heart problems that cause irregular heartbeats and changes in blood pressure, usually lowering blood pressure
  • muscle and joint aches
  • wheezing

The diarrhea associated with MCTs is usually worse after a person eats foods containing a substance called tyramine. Foods that have tyramine include wine, cheese, and chocolate.

Over time, abdominal symptoms related to MCTs can have further harmful effects. These include weight loss because stool passes so fast through your intestines that your body doesn’t have time to absorb nutrients. Dehydration and malnutrition can also occur for similar reasons.

IBS is a condition that affects the large intestine, causing frequent irritation that can lead to constant stomach upset. Examples of symptoms associated with IBS include:

  • constipation
  • cramping
  • diarrhea
  • gas
  • stomach pain

Some people with IBS experience alternating bouts of constipation and diarrhea. As with an MCT, IBS is often made worse when a person eats certain types of foods, such as chocolate and alcohol. Other foods known to cause IBS symptoms include:

  • cruciferous veggies like broccoli, cauliflower, and cabbage
  • spicy foods
  • high-fat foods
  • beans
  • dairy products

IBS doesn’t typically cause physical damage to the intestines. When a person has severe symptoms, a doctor may perform a biopsy of their intestine to look for damage or disease. This is when the doctor might discover an MCT, if one exists.

Considering the symptoms of IBS, it’s easy to see how an MCT may be misdiagnosed as IBS. However, certain key factors may lead a doctor to recommend diagnostic tests to evaluate for an MCT.

Age at diagnosis

While a person can experience IBS at any age, females younger than age 45 are most likely to be diagnosed with IBS, according to the Mayo Clinic. In contrast, the average age a person with an MCT starts to see symptoms is somewhere between 50 and 60.

Flushing, wheezing, or difficulty breathing

A person with an MCT might experience both wheezing and diarrhea and chalk these symptoms up to different issues. For example, they may blame the wheezing on a cold and their diarrhea on IBS. However, the symptoms associated with MCTs aren’t always concentrated on one system in a person’s body.

Knowing this, it’s important you explain all unusual symptoms you’ve been experiencing to your doctor, even if they seem unrelated. For example, you should share if you’ve experienced not only diarrhea, but also flushing, wheezing, or general difficulty breathing. In particular, diarrhea and flushing occur at the same time in 58 percent of those with an MCT.

Weight loss

While a person with IBS may experience weight loss related to their diarrhea, this symptom is more likely to occur with MCTs or another more serious condition. Weight loss is considered a “red flag symptom” that the underlying cause is not IBS, according to the Mayo Clinic.

Continued abdominal symptoms

Often, those with an MCT will experience various abdominal symptoms for many years without a diagnosis. If your symptoms haven’t responded to treatment or only seem to improve with elimination of tyramine-containing substances from your diet, this could be a signal to ask your doctor to keep digging further.

Examples of tests to diagnose an MCT include:

  • measuring your urine for 24 hours for the presence of 5-HIAA, a by-product of your body breaking down serotonin
  • testing your blood for the compound chromogranin-A
  • using imaging scans, such as CT or MRI scans, to identify the potential site of an MCT

The average time from the onset of MCT symptoms to diagnosis is 9 years. While this seems like a very long time, it illustrates just how difficult and sometimes baffling it can be to diagnose an MCT.

If you have symptoms that extend beyond diarrhea, talk to your doctor about doing a workup for MCT. Most people with an MCT don’t seek treatment until the tumor has spread and starts causing additional symptoms. But if you take steps for additional tests early on and your doctor does diagnose MCT, they may be able to remove the tumor, preventing it from spreading.