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ALS is a rare neurological disease that is often hard to diagnose as it mimics symptoms from other neurological and muscle diseases. In this article, we have outlined the process to diagnosis including different tests that are conducted to diagnose ALS.

Amyotrophic lateral sclerosis (ALS) is a rare neurological disease that is characterized by the deterioration of nerve cells, known as motor neurons, that are involved in voluntary muscle movement.

There are two types of motor neurons – lower and upper. The lower motor neurons are located in the spinal cord and brainstem (the lower part of the brain). The upper motor neurons are located in the brain.

In 1990 at a conference in Spain, physicians came up with a set of specific criteria, known as the El Escorial criteria, that need to be met for a diagnosis of ALS. As per the El Escorial criteria, a diagnosis of ALS requires:

  1. Signs that point to the deterioration of lower motor neurons by clinical tests.
  2. Signs that point to degeneration of upper motor neurons by clinical examination.
  3. Signs that the disease is progressive, and spreads from one region to another.
  4. The absence of signs that are indicative of other, similar diseases.

First steps

ALS can be difficult to diagnose early on as it can imitate several other neurological diseases. A diagnosis of ALS is often conducted by ruling out other diseases.

When a patient first presents with symptoms of ALS, physicians will conduct a detailed medical and family history and physical examination.

In the physical exam, the physician, generally a neurologist, will look for specific signs and symptoms of ALS such as:

  • Muscle twitching and spasms
  • Weakness in muscle, which generally starts in one part of the body (i.e. limbs)
  • Loss of muscle mass
  • Unusual, tight and rigid reflexes
  • Pseudobulbar effect (an unusual symptom in which patients experience uncontrollable extreme emotions)

If ALS is suspected, then the physician will conduct a neurologic work-up, which includes tests of muscle and nerve function such as an electromyogram.

Electromyogram (EMG)

An EMG is carried out to help identify abnormalities in the nerve to muscle signaling. EMG assesses the electrical activity of muscles when they contract or when they are relaxed. Essentially, this test measures the capacity of nerves to send signals to muscles in different parts of the body. This test is used to help diagnose several neurological or muscle disorders, including ALS. An EMG is performed by a physician who puts a needle electrode through the skin into different types of muscles and sends small electric shocks to the nerves. If the pattern seen through an EMG is consistent with what it is typically seen in patients with ALS, then extra tests will be ordered.

Tests to exclude other diagnoses

Physicians may also conduct other tests that can help exclude other diagnoses such as:

Magnetic resonance imaging (MRI)

MRI is conducted to image areas of the brain and spinal cord. Patients with ALS actually have normal MRI scans, but MRIs are often conducted to rule out other reasons that can explain the ALS-like symptoms. These diseases include spinal cord tumors, herniated disks in the spine or other conditions.

Spinal tap (lumbar puncture)

This process involves obtaining a sample of the spinal fluid by putting a needle in the spine and removing a small amount of cerebrospinal fluid for tests.

Muscle biopsy

If the physicians believe that symptoms are a result of a different muscle disease, then they may perform a muscle biopsy. A small portion of the muscle is removed when the patient is under local anesthesia and sent to a lab for analysis.

Blood and urine tests

​​While blood tests cannot be not used to detect ALS, they are used to rule other diseases with similar symptoms. Physicians will conduct blood and urine tests that are indicative of other diseases including thyroid disease, low vitamin B12 levels, HIV, hepatitis, and cancer.

Nerve conduction study

This test is also performed to measure nerve to muscle signals. However, only 10% of ALS patients will have abnormal nerve conduction study results. The test can also help indicate the presence of other potential diseases.

Diseases similar to ALS

There are several conditions that have symptoms that imitate those of ALS. Through conducting an extensive work-up, patients can end up having one of these following diseases:

  • Muscular dystrophy
  • Spinal-bulbar muscular atrophy
  • Adult-onset spinal muscular atrophy
  • Myasthenia gravis
  • Tumors
  • Malformations

Second Opinions

As several diseases mimic ALS, if you have have been diagnosed with ALS without significant testing, then it may be worth getting a second opinion.

Unfortunately, there is no one test that can be done to convey an absolute diagnosis of ALS. However, a different neurologist can order a separate round of tests that show something different.

Proof of progression

ALS is a progressive disease, which means its worsens over time. In fact, the major sign of an ALS diagnosis is the worsening of symptoms over time. Therefore, the physician will probably recommend that the patient undergo all the testing in another 6 months to determine whether there has been a change in the disease at all. If the tests indicate that the symptoms have worsened, as have results from the muscle and nerve tests, then the diagnosis will be confirmed.

  • de Carvalho, Mamede, et al. "Electrodiagnostic criteria for diagnosis of ALS." Clinical neurophysiology 119.3 (2008): 497-503.
  • Brooks, Benjamin Rix, et al. "El Escorial revisited: revised criteria for the diagnosis of amyotrophic lateral sclerosis." Amyotrophic lateral sclerosis and other motor neuron disorders 1.5 (2000): 293-299.
  • Mitsumoto, Hiroshi. "Diagnosis and progression of ALS." Neurology 48.4 Suppl 4 (1997): 2S-8S.
  • Swash, Michael. "Early diagnosis of ALS/MND." Journal of the neurological sciences 160 (1998): S33-S36.
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