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Genetic and Rare Diseases Information Center (GARD)

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Primary lateral sclerosis

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Tests & Diagnosis

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How is primary lateral sclerosis diagnosed?

There is no single test that confirms a diagnosis of primary lateral sclerosis (PLS). Because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and amyotrophic lateral sclerosis (ALS), several tests are done to rule out other diseases. After taking a careful record of an individual's medical history and performing a complete neurological examination, a doctor may order the following tests:
  • Blood work. Blood tests are done to check for infections or other possible causes of muscle weakness.
  • Magnetic resonance imaging (MRI) of the brain and spine. An MRI or other imaging tests may reveal signs of nerve cell degeneration and look for other causes of symptoms, such as structural abnormalities, spinal cord compression, multiple sclerosis and spinal cord tumors.
  • Motor and sensory nerve conduction studies. These tests use a low amount of electrical current to test how quickly the nerves carry impulses through the body, and can indicate damage to nerve cells.
  • Electromyogram (EMG). During this test, the doctor inserts a needle electrode through the skin into various muscles. The electrical activity of the muscles is evaluated when they contract and when they're at rest. This test can measure the involvement of lower motor neurons, which can help to differentiate between PLS and ALS.
  • Cerebrospinal fluid (CSF) analysis. An analysis of the CSF, which is taken during a lumbar puncture in the lower back, can help to rule out multiple sclerosis and other causes of spasticity.[1]
After other diseases are ruled out, a doctor may make a preliminary diagnosis of PLS. Sometimes doctors wait three to four years before being sure of the diagnosis, because early ALS can look just like PLS until additional symptoms surface a few years later.[1]
Last updated: 6/6/2011

  1. Primary lateral sclerosis (PLS). Mayo Clinic. October 16, 2010; Accessed 3/30/2011.