Patient Education8 Minute ReadAug | 1 | 2018
How ALS Is Diagnosed
ALS, or amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease, is a neuromuscular disorder affecting motor neurons. These are the nerves responsible for controlling voluntary muscles used for actions such as chewing, talking, and moving your arms and legs. Over time, ALS leads to muscle weakness, eventually impacting breathing, talking, and swallowing.
Although everyone experiences symptoms differently, a common first response to ALS symptoms — muscular weakness, frequent tripping or falling, slurred speech, and/or a change in ability to perform daily tasks such as buttoning clothes or tying shoes — is to attribute these changes to “getting older.”
Over time, an individual or a family member may realize that these symptoms indicate something other than aging. In some cases, difficulty catching breath during routine tasks may also be noticed.
How Is ALS Diagnosed?
An appointment with a primary care physician (PCP) is often the best first step to understanding changes in health and the resulting symptoms.
If ALS is suspected, a PCP will typically refer their patient to a neurologist for further evaluation. This referral can be delayed if symptoms are minor or develop slowly. Patients may wish to consult with other types of doctors for a second opinion. Once symptoms are acknowledged as neurological, consultation with a neurologist is initiated.
A neurologist will perform a detailed physical examination that focuses on muscle strength, reflexes, coordination, and sensation. Typically, a neurologist will perform tests to rule out many of the other possible causes of a patient’s symptoms. The type of symptoms, how fast or how slow they progress and change, and what other disease have to be excluded will affect the time it takes to determine a potential ALS diagnosis.
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Even if other disorders are ruled out, it may still be difficult to definitely determine a diagnosis of ALS. As a next step, individuals are often referred to a neuromuscular specialist, which is a doctor that specializes in nerves and muscles. The neuromuscular specialist will either assist in ALS testing or offer a second opinion.
To do so, they will review the results from the previously performed tests. They may also repeat some of the tests to assess potential changes. A consultation with a neuromuscular specialist ensures a comprehensive and thorough medical evaluation for ALS.
ALS Diagnosis Steps
Step 1: Have a Neurological Exam
The diagnosing ALS process begins with an examination by a neurologist. This will include a detailed review of the patient’s family, work, and environmental history. During the exam, the neurologist will look for typical features of ALS, such as:
- Muscle weakness, which is often only on one side of the body, such as one arm or one leg.
- Vocal changes, especially slurred words or slow speech.
- Muscle changes affecting the mouth, tongue, chewing, and swallowing functions.
- Lower motor neuron (LMN) features, such as muscle shrinkage or twitches. These twitches are called fasciculations and may occur when muscles contract without full control from the nerve cells.
- Upper motor neuron (UMN) features, such as hyperactive reflexes and muscle spasticity, which is a type of tightness and rigidity of the muscles
- Emotional changes resulting in the loss of some control of emotional responses, such as uncontrollable crying or laughing.
- Changes in thinking, such as loss of good judgment or common social skills
- Problems in verbal fluency and word recognition abilities. These symptoms are less common or may be present but not readily noticeable.
- Pain, loss of sensation, or extra-pyramidal rigidity, which is a different type of muscle rigidity that is frequently seen in Parkinson’s type disorders
Step 2: Undergo Diagnostic ALS Testings
The next step to diagnose ALS often involves a series of tests. These typically include an MRI (magnetic resonance imaging) of the neck, and sometimes of the head and lower spine, along with an EMG (electromyography) which tests nerve conduction, and a series of blood tests.
Sometimes urine tests, genetic tests, or a lumbar puncture (also called a spinal tap) are also necessary.
Electromyography (EMG)
The EMG is a very important part of the diagnostic process for ALS.
In the first part of the EMG, small electric shocks are sent through the nerves to measure their conduction speed and detect any potential nerve damage. The shocks are often similar to static electricity but may sometimes feel a bit stronger. This phase of the test determines whether the individual has “nerve block,” which is a feature of a different disease called multifocal motor neuropathy. There is a chart at the end of this section that further explains this disease. It also tests whether the nerves that communicate sensation are affected, which may also indicate a disease other than ALS.
In the second part of the EMG, the electrical activity of specific muscles is tested by inserting a very fine needle into them. The needle is used to assess the pattern of electrical activity in these muscles. Unlike the first part of the test, no electric shocks are involved, and the needle does not inject or extract anything from your muscles.
MRI
An MRI is a painless, non-invasive procedure that offers a very detailed picture of the spinal cord, the nerves that come out of the spinal cord, and the bones and connective tissues that surround and protect the spinal cord. It shows more detail than a CAT (computed axial tomography) scan or X-rays. The MRI will help rule out conditions like pressure on the spinal cord or major nerves (such as from a herniated vertebral disk), multiple sclerosis, and tumors or bony abnormalities that might compress the nerves. Additionally, it can help detect vascular changes and strokes that may impact the spinal cord or brain.
The MRI procedure takes about 30 minutes to complete. Patients will be asked to recline inside a machine that is basically a large, rotating magnet. The test is noisy, but painless. If individuals experience discomfort in small, confined spaces, it's crucial to inform the doctor before the MRI starts. This allows for the possibility of providing medication to help the person relax.
Lab Tests
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Blood and Urine Tests: Blood tests are used to look for evidence of other diseases whose symptoms are similar to early signs of ALS. These include tests for thyroid and parathyroid disease, vitamin B12 deficiency, HIV, hepatitis, auto-immune diseases, and some types of cancer. Creatine kinase (CK), an enzyme released when muscles are injured or die, is also measured.
Specialized blood tests are also performed, such as autoimmune antibody tests, anti-GM1 antibody tests, and tests looking for high levels of protein in the blood and urine that may be related to some types of cancers. Depending on the individual’s work and environmental history, the doctor may also test his or her urine for heavy metals.
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Genetic Tests: In some rare cases, genetic tests and tests of hexosaminidase A levels, which can be related to juvenile spinal muscle atrophy, may also be performed. Genetic testing for ALS is usually only done when someone else in the family has ALS.
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Spinal Tap (Lumbar Puncture): Occasionally, a lumbar puncture (also called a spinal tap) may be required. For this test, a small needle is inserted into the lowest part of the spine (below the spinal cord) to remove fluid which will be examined for abnormal cells. A lumbar puncture is usually done only if the individual has unusual features of ALS, such as spinal nerve abnormalities, or has no sign of abnormal reflexes or spasticity.
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Muscle Biopsy: Rarely, some people who have uncommon patterns of weakness, pain, or very high CK levels may need a muscle biopsy to look for muscle-specific diseases.
Step 3: Receive a Diagnosis
Once these tests have been completed, the neurologist may be able to tell whether an individual has ALS. Sometimes, not all of the symptoms and findings that are required to make the ALS diagnosis are present, especially in the early phase of the disease. In this case, the neurologist will repeat the physical and neurological exams and the EMG at a later date to look for changes over time.
Conditions with Overlapping Symptoms in ALS Diagnosis
The chart below explains some of the alternative diseases that neurologists look for when trying to determine whether an individual has ALS. These disorders share some symptoms that resemble those seen in ALS.
| Symptoms | Disorders with Features Similar to ALS | Test(s) |
| Weakness in one arm or leg with muscle wasting | Multifocal motor neuropathy | EMG, GM1 antibody tests |
| Numbness in the arms and body, neck pain, past injury to the neck | Cervical spine injury with radiculopathy | MRI of the neck |
| Fine tremors of the muscle | Benign fasciculations (no muscle weakness or muscle wasting and tremors do not worsen) | EMG |
| Muscle weakness in arms or legs close to the body rather than at the far extremities. Sometimes there is muscle pain. Symptoms change slowly over time | Inclusion body myositis (inflammation of the muscles) | Blood tests, muscle biopsy |
| Double vision, droopy eyelids, muscle weakness that gets dramatically worse with prolonged effort | Myasthenia gravis | EMG, blood tests |
| Muscle atrophy (muscle shrinkage, weakness and loss of function), past history of polio | Post-polio progressive muscular atrophy | EMG |
| Men only: difficulty swallowing, difficulty walking, breast enlargement | Kennedy syndrome (bulbospinal muscular atrophy) | Genetic test, blood test |
| Problems with balance, speech and swallowing difficulties, cognitive decline, sometimes psychosis | Late onset Tay-Sachs disease | Blood test, MRI |
| Anemia, weight loss, sometimes fevers and chills, headache and stiff neck | Motor neuron syndromes associated with lymph cancers (lymphomas, multiple myeloma, some leukemias) | Blood tests, urine test, sometimes a lumbar puncture, MRI and bone scans |
| Anemia, weight loss, often with sensory changes, sometimes with unsteadiness | Syndromes associated with and caused by lung, breast, and other cancers | Blood tests, X-rays and CT scans of the chest, mammogram, colonoscopy |
| Muscle weakness and tremors, heat intolerance, heart palpitations | Thyroid disease of an overactive thyroid (hyperthyroidism) | Blood test |
Modified from Layzer, RB. Chapter 415. Heredity and acquired intrinsic motor neuron diseases. In: Bennett and Plum (Eds), Cecil Textbook of medicine, W.B. Saunders, Philadelphia 1999.
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