There is no single test to diagnose amyotrophic lateral sclerosis (ALS) because it shares common symptoms with other neurological diseases. Instead, the diagnosis is based on a period of observation to track the progression of symptoms, combined with a series of clinical tests to rule out other conditions. Observation can take up to a year, which can result in a diagnosis taking from 12 to 14 months in the United States.

The El Escorial criteria, revised by the World Federation of Neurology (WFN) in 2010, defines the following conditions for a diagnosis of ALS:

  • Signs of degeneration of the lower motor neurons (LMN) in the spinal cord and brainstem, and of the upper motor neurons (UMN) in the brain. Motor neurons are nerve cells whose cell body is located in the spinal cord and whose fiber (axon) projects outside the spinal cord to control the movement of muscles.
  • The progressive spread of signs within a region, or to other regions of the body.
  • No evidence of other disease processes that could explain the symptoms.

A diagnosis of ALS can be defined as clinically definite, probable, possible, or suspected, depending on the progression of the LMN and UMN degradation and the results of electromyography testing. Because a definitive ALS diagnosis is not always possible, individuals may benefit from a second neurological opinion.

For a full ALS diagnosis, clinical tests to rule out other neurological diseases will be carried out based on the symptoms the patient has shown. These can include:

  • Electromyography (EMG), to assess the electrical activity in the muscle. Abnormal EMG results can confirm LMN degeneration for the diagnosis of ALS.
  • Nerve conduction study (NCS), which measures the ability of a nerve to transmit an electrical signal to other areas of the body. This can exclude disorders that effect the peripheral nerves.
  • Magnetic resonance imaging (MRI), a noninvasive method to produce detailed images of the brain and spinal cord. People with ALS generally show normal MRI scans, but this can reveal other treatable causes behind the symptoms, such as syringomyelia (a cyst in the spinal cord).
  • In rare cases, a muscle biopsy will be performed. A small section of muscle is removed from the patient under local anesthesia and examined under a microscope for abnormalities.
  • Blood and urine testing, for example for thyroid function.
  • Spinal tap (or lumbar puncture) to exclude inflammatory nerve conditions.
  • Tests for infectious diseases such as human immunodeficiency virus (HIV) and human T-cell leukemia virus (HTLV), which can cause some ALS-like symptoms.

ALS News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.