How is ALS Diagnosed?
To be diagnosed with ALS, people must have signs and symptoms of both upper and lower motor neuron damage that cannot be attributed to other causes. No single test can provide a definitive diagnosis of ALS; instead, the diagnosis of ALS is primarily based on the symptoms and signs the physician observes in the patient and a series of tests to rule out other diseases. Physicians obtain the individual’s full medical history and usually conduct a neurologic examination at regular intervals to assess whether symptoms such as muscle weakness, atrophy of muscles, hyperreflexia and spasticity are getting progressively worse.
Since 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 must be conducted to exclude the possibility of other conditions. One of these tests is electromyography (EMG), a special recording technique that detects electrical activity in muscles. Certain EMG findings can support the diagnosis of ALS. Another common test is a nerve conduction study (NCS), which measures electrical energy by assessing the nerve’s ability to send a signal. Specific abnormalities in the NCS and EMG may suggest, for example, that the individual has a form of peripheral neuropathy (damage to peripheral nerves) or myopathy (muscle disease) rather than ALS.
The physician may order magnetic resonance imaging (MRI), a noninvasive procedure that uses a magnetic field and radio waves to take detailed images of the brain and spinal cord. Standard MRI scans are normal in people with ALS. However, they can reveal evidence of 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).
Based on the person’s symptoms and findings from the examination and from these tests, the physician may order tests on blood and urine samples to eliminate the possibility of other diseases as well as routine laboratory tests. In some cases, for example, if a physician suspects that the individual may have a myopathy rather than ALS, a muscle biopsy may be performed.
Infectious diseases such as human immunodeficiency virus (HIV), human T-cell leukemia virus (HTLV), polio, West Nile virus, and Lyme disease can cause ALS-like symptoms in some cases. Neurological disorders such as multiple sclerosis, post-polio syndrome, multifocal motor neuropathy, and spinal muscular atrophy also can mimic certain facets of the disease and should be considered by physicians attempting to make a diagnosis. Fasciculations, the fine rippling movements in the muscle, 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.