Learn about ALS
Diagnosis
No test can provide a definite diagnosis of ALS, although the presence of upper
and lower motor neuron signs in a single limb is strongly suggestive. 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 patient'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.
MRI (axial FLAIR) demonstrates increased T2 signal within the posterior part of
the internal capsule, consistent with the clinical diagnosis of ALS.
Because symptoms of ALS 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 measures nerve
conduction velocity (NCV). Specific abnormalities in the NCV results may suggest,
for example, that the patient 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. Although these
MRI scans are often normal in patients with ALS, they can reveal evidence of other
problems that may be causing the symptoms, such as a spinal cord tumor, multiple
sclerosis, a herniated disk in the neck, syringomyelia, or cervical spondylosis.
Based on the patient'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 patient may have a myopathy rather
than ALS, a muscle biopsy may be performed.
Infectious diseases such as human immunodeficiency virus (HIV), human T-cell leukaemia
virus (HTLV), Lyme disease, syphilis and tick-borne encephalitis viruses can in
some cases cause ALS-like symptoms. Neurological disorders such as multiple sclerosis,
post-polio syndrome, multifocal motor neuropathy, CIDP, and spinal muscular atrophy
can also mimic certain facets of the disease and should be considered by physicians
attempting to make a diagnosis.
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, patients should
always obtain a second neurological opinion.
