Diagnosis

There is no single test that confirms a diagnosis of primary lateral sclerosis (PLS). In fact, because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and ALS, your doctor is likely to order several tests to rule out other diseases.

After taking a careful record of your medical history and family history and performing a neurological examination, your doctor might order the following tests:

• Bloodwork. Blood tests check for infections or other possible causes of muscle weakness.
• MRI. An MRI or other imaging tests of your brain or spine might reveal signs of nerve cell degeneration. An MRI can also show other causes of your symptoms, such as structural abnormalities, multiple sclerosis or spinal cord tumors.
• Electromyogram (EMG). During an EMG, your doctor inserts a needle electrode through your skin into various muscles. The test evaluates the electrical activity of your muscles when they contract and when they're at rest. This test also measures the involvement of lower motor neurons, which can help to differentiate between PLS — an upper motor neuron disease — and ALS, which affects both upper and lower motor neurons.
• Nerve conduction studies. These tests use a low amount of electrical current to measure your nerves' ability to send impulses to muscles in different areas of your body. This test can determine if you have nerve damage.
• Spinal tap (lumbar puncture). Your doctor uses a thin, hollow needle inserted into your spinal canal to remove small samples of the fluid that surrounds your brain and spinal cord (cerebrospinal fluid) for laboratory analysis. A spinal tap can help rule out multiple sclerosis, infections and other conditions.

Sometimes doctors wait 3 to 4 years before finalizing a diagnosis because early ALS can look just like PLS until additional symptoms surface a few years later. You might be asked to return for repeat electromyography testing over 3 to 4 years before the PLS diagnosis is confirmed.

Genetic testing may be done when juvenile PLS is suspected. Genetic counseling also may be recommended.