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Revised Electrophysiological Criteria for Diagnosis of ALS
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Inclusion of fasciculation potentials as evidence for denervation, will dramatically increase the diagnostic sensitivity of EMG in patients with motor neuron disease.
Source: Douglass CP, et al. An evaluation of neurophysiological criteria used in the diagnosis of motor neuron disease. J Neurol Neurosurg Psychiatry 2010;81:646-649. doi: 10.1136/jnnp.2009.197434.
Electrodiagnostic confirmation of amyotrophic lateral sclerosis (ALS), based on El Escorial criteria established in 1994, revised in 1998, and currently the most commonly used in clinical studies and therapeutic trials, requires that lower motor neuron electromyographic (EMG) abnormalities in the form of positive sharp waves or fibrillation potentials be found in at least two muscles of three limbs, or two limbs and thoracic paraspinal or cranial innervated muscles, and that the two abnormal muscles be innervated by different nerve roots and different peripheral nerves. Fasciculation potentials are not accepted as evidence of denervation. Studies have demonstrated that, when patients' records are examined, El Escorial criteria remain a poor diagnostic indicator and entry into clinical trials is consequently delayed (Neuroepidemiology 2002:21:265-70). Might new criteria allow earlier diagnosis of ALS?
Awaji-shima, Japan, was the setting for an international symposium in 2006 where revised criteria were proposed to enhance ALS diagnostic sensitivity, including considering a limb abnormal based on either clinical or electrodiagnostic abnormalities, and considering unstable, complex fasciculation potentials equivalent to positive sharp waves as evidence of denervation. Among 205 consecutive suspected motor neuron disease (MND) patients seen at the Royal Hallamshire Hospital, Sheffield, UK, and retrospectively reviewed, EL Escorial criteria were compared to these new proposals with respect to their sensitivity and specificity.
Motor neuron disease was the working diagnosis in 107, with neuropathy (n = 22), radiculopathy (n = 19), benign fasciculation syndrome (n = 6), and no specific disease (n = 51) making up the remaining patients. Mean age of MND patients was 64.3 years, mean duration from symptom onset to presentation was 17.9 months, and male to female ratio was 3:1. Using revised El Escorial clinical and EMG criteria, and considering all 205 patients, 21 and 12 patients were diagnosed with probable and definite MND, respectively, totaling 34 patients deemed MND positive. One hundred and one (101) patients were diagnosed with possible MND and 70 patients had no definite diagnosis. These latter two groups, encompassing 171 patients, were deemed to be MND negative. Using Awaji-shima criteria, 54 and 15 patients were diagnosed with probable and definite MND, respectively, totaling 69 patients deemed MND positive, while 67 were diagnosed with possible MND and 69 with no definite diagnosis, encompassing 136 patients deemed to be MND negative. Awaji-shima criteria would have doubled the number of patients eligible for ALS therapeutic trials, with a sensitivity of 60.7% for MND, vs. 28% for the revised El Escorial criteria. Both had a specificity of 95.9% with no difference in false positive rate. Awaji-shima criteria, accepting fasciculation potentials as evidence of denervation, allow earlier MND diagnosis and increases diagnostic certainty.
During needle electromyographic (EMG) study, how long must the electrode be left intramuscularly to reliably conclude that no fasciculation potentials are present? To answer this question, a small prospective study was undertaken (Mills KR. J Neurol Neurosurg Psychiatry 2010;doi:10.1136/jnnp.2009.186833). Among 19 patients with definite amyotrophic lateral sclerosis based on El Escorial criteria, 53 muscles were examined using a concentric needle, including the biceps (n = 8), tibialis anterior (n = 27), first dorsal interosseous (n = 17), and trapezius (n = 1). Recordings were obtained for up to 776.8 seconds with the longest inter-fasciculation interval found to be 92.2 seconds, suggesting that observation for up to 90 seconds may be necessary to reliably exclude the presence of fasciculation potentials in ALS patients.