, Ali T. Ghouse2 and Raghav Govindarajan3
(1)
Parkinson’s Clinic of Eastern Toronto and Movement Disorders Centre, Toronto, ON, Canada
(2)
McMaster University Department of Medicine, Hamilton, ON, Canada
(3)
Department of Neurology, University of Missouri, Columbia, MO, USA
Amyotrophic Lateral Sclerosis
Electrodiagnostic tests are essential for the diagnostic workup of a patient with suspected amyotrophic lateral sclerosis (ALS). It is also important to exclude other conditions such as myopathy, neuromuscular transmission disorders, demyelinating polyneuropathy, plexopathy, and radiculopathy.
Lambert Criteria [2] (1969)
First, the sensory nerve conduction studies are normal.
Second, the motor nerve conduction velocities (CVs) that are recorded from relatively unaffected muscles are normal, and when the CVs are recorded from severely affected muscles they are not less than 70 % of the average normal value.
Third, fibrillation and fasciculation potentials are present in muscles of the upper and lower extremities or in the muscles of the head and the extremities.
Fourth, motor unit potentials are reduced in number and increased in duration and amplitude.
Revised El Escorial Criteria for ALS [1] (1994)
Needle electromyography (EMG) examination shows evidence of active and chronic denervation in at least two of the four following regions: (1) brain stem, (2) cervical, (3) thoracic, and (4) lumbosacral. For the brain stem region, needle EMG abnormalities are required in one muscle only. For the thoracic region, abnormalities can be in the paraspinal muscles below the T6 level or in the abdominal muscles. For the cervical and the lumbosacral paraspinal regions, the abnormalities must be present in more than two muscles innervated by two different nerve roots and peripheral nerves. Needle examination of the sternocleidomastoid muscle has sensitivity similar to that for examination of the tongue in patients with bulbar symptoms [3].
Airlie House Criteria (2008)
Principles
To make the diagnosis of ALS: First there should be evidence of lower motor neuron (LMN) degeneration shown by clinical, electrophysiological, or neuropathological examination. Second, there should be evidence of upper motor neuron (UMN) degeneration shown by clinical examination, and progressive spread of symptoms or signs within a region or to other regions, as determined by history, physical examination, or electrophysiological tests.
Furthermore, there should not be any electrophysiological or pathological evidence of other disease processes that might explain the signs of UMN or LMN degeneration. Also, there is no neuroimaging evidence of other disease processes that might explain the observed clinical and electrophysiological signs.
Diagnostic Categories
Clinically definite ALS is defined by clinical or electrophysiological evidence of the presence of LMN and UMN signs in the bulbar region and in at least two spinal regions, or the presence of LMN and UMN signs in three spinal regions.
Clinically probable ALS is defined by clinical or electrophysiological evidence of LMN and UMN signs in at least two regions, with some UMN signs necessarily above the LMN signs.
Clinically possible ALS is defined when clinical or electrophysiological signs of UMN and LMN dysfunction are found in only one region; or UMN signs are found alone in two or more regions; or LMN signs are found above the UMN signs. Neuroimaging and clinical laboratory studies will have been performed and other diagnoses must have been excluded.
Criteria for Detection of Neurogenic Changes by Needle EMG in Diagnosis of ALS
First, for the evaluation of lower motor neuron disease in ALS in any given body region, clinical and electrophysiological abnormalities have equal diagnostic significance. Second, EMG features of chronic neurogenic changes must be found; such as: (1) motor unit potentials (MUPs) of increased amplitude and duration are usually present with an increased number of phases, as assessed by qualitative or quantitative studies; (2) there is reduced motor unit recruitment, defined by the rapid firing of a reduced number of motor units. In limbs affected by clinical features of significant upper motor neuron abnormalities, rapid firing may not be achieved; and (3) unstable and complex MUPs are present in most cases of ALS when a narrow band pass filter (500 Hz to 5 KHz) is used). Third, in ALS, fibrillation and positive waves are usually recorded in strong, non-wasted muscles. Finally, the presence of chronic neurogenic changes on needle EMG in ALS, such as fasciculation potentials, preferably of complex morphology, is equivalent in clinical significance to fibrillations and positive sharp waves.
Use of Nerve Conduction Studies in ALS: Exclusion of Other Disorders
The following findings are compatible with ALS:
- 1.
Normal sensory nerve action potential (SNAP) amplitude and normal sensory CVs in the absence of concomitant entrapment or other neuropathies. Mildly reduced SNAP amplitudes and CVs in the presence of neuropathy of identifiable etiology are acceptable.Related posts:
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