TUESDAY, Nov. 3, 2026 (HealthDay News) — Getting the right diagnosis isn’t always easy. Some illnesses develop slowly, some have vague symptoms, and many can be mistaken for something else.
Actress Christina Applegate’s story about being misdiagnosed with multiple sclerosis (MS) reminds us that even doctors can struggle to find the right answer. Misdiagnosis can happen to anyone, with any condition.
How Common Is Misdiagnosis?
A misdiagnosis means your doctor didn’t get it right the first time — maybe the diagnosis was missed, incorrect or took too long. It happens more often than you might think, especially with tricky conditions that share symptoms.
About 1 in 20 U.S. adults has a diagnostic error in outpatient care each year. That is roughly 12 million people.
An older estimate suggests that about 1 in 10 diagnoses is probably wrong. Experts say most people will have at least one diagnostic error in their lifetime.
Error rates are similar across settings: about 6% in primary care, about 6% in emergency departments and about 8% in hospital autopsy studies.
One analysis estimated that about 550,000 to 800,000 Americans die or are permanently disabled each year because of diagnostic errors.
It’s important to keep these numbers in perspective. With more than 1 billion healthcare visits in the United States each year, the risk for serious harm from a misdiagnosis at any single visit is less than 0.1%. The researchers behind these estimates emphasize that patients shouldn’t panic or lose trust in their healthcare providers.
Which Conditions Are Most Often Missed?
Most diagnostic errors involve common conditions, not rare ones. These include infections, heart and blood vessel disease and cancer. Some conditions are more likely to cause serious harm from misdiagnosis: stroke, sepsis, pneumonia, blood clots (venous thromboembolism) and lung cancer.
Cancers are among the diagnoses most often missed or delayed, especially colorectal, lung, breast, prostate and bladder cancer. Heart attack, stroke, sepsis, pulmonary embolism and brain bleeding are also on this list.
In primary care, the conditions missed most often were pneumonia and worsening heart failure. Even so, together they made up less than 13% of errors, because many different conditions were involved.
In clinical practice, some typical ways I've seen one condition mistaken for another include:
Colon cancer attributed to hemorrhoids
Bipolar disorder diagnosed as depression
A lung tumor read as pneumonia on a chest X-ray
Blood in the urine blamed on a urinary infection when the cause is bladder cancer
A new symptom blamed on an existing chronic disease. For example, cough and weight loss may be attributed to chronic obstructive pulmonary disease when lung cancer is the cause.
MS: An Example Of Misdiagnosis In Both Directions
MS is a good example of how a diagnosis can go wrong in more than one way.
Diagnosed when it isn't there: A review of pooled studies worldwide revealed that about 15% of people diagnosed with MS did not actually have it. It took a few months to almost 16 years to correct the errors. Women were about twice as likely as men to be misdiagnosed with MS.
Missed when it is there: Real MS can also go unrecognized at first. In those cases, the correct diagnosis took an average of about 17 months.
What gets mistaken for MS: The most common conditions mistaken for MS are migraine, fibromyalgia, nonspecific symptoms together with an abnormal magnetic resonance imaging (MRI) finding, functional neurological disorders, and neuromyelitis optica spectrum disorder (NMOSD). About a third of misdiagnosed patients were harmed, often by MS medicines they didn't need.
Why Do Misdiagnoses Happen?
Diagnostic errors usually come from several problems combined, not from one mistake:
Thinking errors: The most common error is not considering the right diagnosis in the first place. Another is "premature closure," which means settling on an answer too soon.
Atypical or vague symptoms: Errors are more likely when symptoms are unusual or don't seem related to the actual disease.
Problems with testing and follow-up: These include tests that are never ordered, results that are misread and abnormal results that are not followed up.
System pressures: Time pressure, heavy workloads, poor communication and poorly designed electronic records all contribute.
Limits of tests: A normal result does not always rule out disease. A breast lump can still be cancer even when the mammogram is normal.
How You Can Advocate For Yourself
Keep a record of your symptoms — when they started, how they have changed and how you have responded to treatment.
Ask how the diagnosis was reached. For example: "What else could this be?" and "What would make you reconsider this diagnosis?"
Follow up on test results. Don't assume no news is good news.
Mention symptoms that don't fit, even if they seem unrelated.
Consider a second opinion if symptoms don't match the diagnosis, treatment isn't helping or the condition is serious or uncommon. Ask whether your imaging or pathology slides can be reviewed again.
Bring someone with you to appointments to help you remember what was discussed.
What Should You Do If Symptoms Get Worse?
Tell your doctor promptly about new or worsening symptoms. Ask whether more testing, a referral or a fresh review of your case makes sense. Get urgent care right away for warning signs such as sudden weakness, numbness, trouble speaking, chest pain, severe headache or fever with confusion.
Don't stop or change prescribed medication on your own while seeking another opinion. Make changes together with your care team.
Partnering With Your Healthcare Team
Write down your questions before each visit, and be open about how symptoms affect your daily life. Good diagnoses come from combining your experience with careful medical evaluation. Asking questions and requesting a second look are part of getting the right care, not a sign of distrust.
More information
The AARP has more information on the diagnoses doctors often miss.
SOURCES: Multiple Sclerosis Journal, Sept. 8, 2024; Nature Reviews Neurology, Aug. 11, 2017; Neurology, Jan. 1, 2019; The New England Journal of Medicine, Dec. 24, 2015; Journal of the American Medical Association, Jan. 27, 2023; Journal of the American Medical Association, July 26, 2023; Journal of International Medical Research, Aug. 21, 2023; Neurology, Sept. 27, 2016; JAMA Internal Medicine, March 25, 2013; BMJ Quality & Safety, Jan. 19, 2024
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