Diagnosis of Amyotrophic Lateral Sclerosis
No one test can provide a definitive diagnosis of ALS. ALS is primarily diagnosed based on detailed history of the symptoms and signs observed by a physician during physical examination along with a series of tests to rule out other mimicking diseases. However, the presence of upper and lower motor neuron symptoms strongly suggests the presence of the disease.

Physicians will review an individual’s full medical history and conduct a neurologic examination at regular intervals to assess whether symptoms such as muscle weakness, atrophy of muscles, and spasticity are getting progressively worse.

ALS symptoms in the early stages of the disease can be similar to those of a wide variety of other, more treatable diseases or disorders.  Appropriate tests can exclude the possibility of other conditions.

Muscle and imaging tests
Electromyography (EMG), a special recording technique that detects electrical activity of muscle fibers, can help diagnose ALS. Another common test is a nerve conduction study (NCS), which measures electrical activity of the nerves and muscles by assessing the nerve’s ability to send a signal along the nerve or to the muscle. Specific abnormalities in the NCS and EMG may suggest, for example, that the individual has a form of peripheral neuropathy (damage to peripheral nerves outside of the brain and spinal cord) or myopathy (muscle disease) rather than ALS.

A physician may also order a magnetic resonance imaging (MRI) test, a noninvasive procedure that uses a magnetic field and radio waves to produce detailed images of the brain and spinal cord. Standard MRI scans are generally normal in people with ALS. However, they can reveal other problems that may be causing the symptoms, such as a spinal cord tumor, a herniated disk in the neck that compresses the spinal cord, syringomyelia (a cyst in the spinal cord), or cervical spondylosis (abnormal wear affecting the spine in the neck).

Laboratory tests
Based on the person’s symptoms, test results, and findings from the examination, a physician may order tests on blood and urine samples to eliminate the possibility of other diseases.

Tests for other diseases and disorders
Infectious diseases such as human immunodeficiency virus (HIV), human T-cell leukemia virus (HTLV), polio, and West Nile virus can, in some cases, cause ALS-like symptoms. Neurological disorders such as multiple sclerosis, post-polio syndrome, multifocal motor neuropathy, and spinal and bulbar muscular atrophy (Kennedy’s disease) also can mimic certain features of the disease and should be considered by physicians attempting to make a diagnosis. Fasciculations and muscle cramps also occur in benign conditions.

Because of the prognosis carried by this diagnosis and the variety of diseases or disorders that can resemble ALS in the early stages of the disease, individuals may wish to obtain a second neurological opinion.