Multiple sclerosis (MS) is a hard disease to diagnose. If you have symptoms of MS and go to an MS treatment center, there's about a 50% chance that you will not receive a diagnosis of MS. That’s because lots of other conditions mimic MS. In fact, one criterion for an MS diagnosis is that your doctor must rule out the other suspects.
A differential diagnosis is when doctors suspect several possible diseases or conditions could be causing symptoms. With MS, there are lots of possibilities that doctors must consider. They include blood vessel problems, infections, other autoimmune diseases, vitamin deficiencies, and inherited conditions.
1. Systemic Lupus Erythematosus (SLE)
Like MS, SLE is a disease of the immune system. That means your immune system malfunctions and attacks healthy parts of your body. SLE can cause many symptoms that mimic MS. In fact, SLE can cause so many different symptoms that people call it “the great imitator.” Possible symptoms include numbness, tingling and fatigue.
Sarcoidosis is a disease that is usually occurs during young adulthood. Like MS, it is an immune system disease. It often affects the lungs and the skin, but it can also affect the brain. Sarcoidosis can cause visual symptoms and fatigue that mimic MS. It typically appears between ages 20 and 40.
3. Myasthenia Gravis
This disease causes slowing of nerve signals to muscles. Symptoms can be similar to MS and include weakness, fatigue, and intolerance of heat.  Like MS, myasthenia gravis occurs often in young women. It may cause visual disturbances and trouble swallowing. It is also an immune system disease and is difficult to diagnose, frequently leading to a missed or delayed diagnosis.
HTLV-1 stands for human T-cell lymphotrophic virus-1. This infection can look very much like advanced MS because it can cause muscles spasms, weakness, and paralysis. A blood test can rule out this MS mimic. HTLV-1 is more common in IV drug users and people who have traveled in southern parts of the world, such as the Caribbean, Africa, and South America.
This sexually transmitted disease (STD) can mimic MS if it spreads to the central nervous system, a condition called neurosyphilis. Symptoms can include numbness, confusion, trouble walking, weakness, and tremors. It may take 10 to 20 years after initial infection for symptoms of neurosyphilis to show up. This MS mimic is not very common today, but it does exist. A blood test can diagnose it.
6. Lyme Disease
Lyme disease is an infection from a tick bite. The bacterium that causes Lyme disease can travel through the bloodstream and bring on many symptoms that mimic MS. These include numbness, tingling, fatigue, a stiff neck, and facial palsy. You might suspect Lyme disease if you live near or spend time in woods or fields where deer are common.
7. Vitamin B12 Deficiency
Vitamin B12 deficiency may cause demyelination, which is loss of the protective lining around nerves, or myelin. Demyelination also occurs in MS, so symptoms can be very similar. They include numbness, tingling, and weakness in the legs and arms. Mental confusion may also occur. You can get B12 only through foods such as meat and dairy products. Vegetarians are most likely to be low on B12.
8. Blood Vessel Problems
Several types of blood vessel problems in the brain or spine can mimic MS. This includes stroke from bleeding or clotting inside the brain. Stroke symptoms that mimic MS include visual changes, trouble walking, dizziness, and mental changes. Blood vessel problems also can occur in the spinal cord, decreasing the blood supply to the cord and its nerves. This causes symptoms similar to progressive MS.
There is no single test that can diagnose MS. To rule out other causes of MS symptoms, your doctor may use blood tests, imaging studies, a spinal tap, and nerve conduction studies. A complete history and physical exam by an MS specialist, called a neurologist, is essential. Ruling out other conditions in the differential diagnosis is an important part of getting to the right diagnosis.
Many people who have symptoms of MS turn out to have something else.
Many other conditions can mimic MS. As a result, ruling out other conditions is a vital part of an MS diagnosis.
To diagnose MS, a neurologist will use a variety of tests and perform a complete neurological evaluation.