Analysis of the compound muscle action potential scan: Step index (STEPIX) and amplitude index (AMPIX). 2022

Sanjeev D Nandedkar, and Paul E Barkhaus, and Erik V Stålberg
Natus Medical Inc, Hopewell Junction, New York, USA; Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA. Electronic address: Sanjeev.nandedkar@natus.com.

The compound muscle action potential (CMAP) scan is useful to study motor unit (MU) loss. It is of interest to develop simple measurements of the scan. CMAP scan recordings were performed in the abductor pollicis brevis muscle of 20 control subjects and 26 patients with amyotrophic lateral sclerosis (ALS). They were analyzed using two new measurements called Step index (STEPIX) reflecting the number of steps, and Amplitude index (AMPIX) for amplitude of these steps. In control subjects, STEPIX ranged from 71 to 172 while AMPIX was 78-158 µV. In ALS patients STEPIX was reduced and AMPIX was increased. The degree of change in STEPIX and AMPIX varied among patients reflecting the success or failure of reinnervation. Follow up studies in 9 muscles demonstrated reduced STEPIX and increased AMPIX despite minimal change in the CMAP. STEPIX and AMPIX are deterministic measurements of the CMAP scan made using a spreadsheet program. STEPIX and AMPIX can be inferred as indices for the number of motor units and their size, and demonstrate the expected pattern in ALS patients. The new algorithm for CMAP scan analysis may be useful to study disease progression in patients with ALS.

UI MeSH Term Description Entries
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000200 Action Potentials Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli. Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000465 Algorithms A procedure consisting of a sequence of algebraic formulas and/or logical steps to calculate or determine a given task. Algorithm
D000690 Amyotrophic Lateral Sclerosis A degenerative disorder affecting upper MOTOR NEURONS in the brain and lower motor neurons in the brain stem and SPINAL CORD. Disease onset is usually after the age of 50 and the process is usually fatal within 3 to 6 years. Clinical manifestations include progressive weakness, atrophy, FASCICULATION, hyperreflexia, DYSARTHRIA, dysphagia, and eventual paralysis of respiratory function. Pathologic features include the replacement of motor neurons with fibrous ASTROCYTES and atrophy of anterior SPINAL NERVE ROOTS and corticospinal tracts. (From Adams et al., Principles of Neurology, 6th ed, pp1089-94) ALS - Amyotrophic Lateral Sclerosis,Lou Gehrig Disease,Motor Neuron Disease, Amyotrophic Lateral Sclerosis,Amyotrophic Lateral Sclerosis With Dementia,Amyotrophic Lateral Sclerosis, Guam Form,Amyotrophic Lateral Sclerosis, Parkinsonism-Dementia Complex of Guam,Amyotrophic Lateral Sclerosis-Parkinsonism-Dementia Complex 1,Charcot Disease,Dementia With Amyotrophic Lateral Sclerosis,Gehrig's Disease,Guam Disease,Guam Form of Amyotrophic Lateral Sclerosis,Lou Gehrig's Disease,Lou-Gehrigs Disease,ALS Amyotrophic Lateral Sclerosis,Amyotrophic Lateral Sclerosis Parkinsonism Dementia Complex 1,Amyotrophic Lateral Sclerosis, Parkinsonism Dementia Complex of Guam,Disease, Guam,Disease, Lou-Gehrigs,Gehrig Disease,Gehrigs Disease,Sclerosis, Amyotrophic Lateral
D018450 Disease Progression The worsening and general progression of a disease over time. This concept is most often used for chronic and incurable diseases where the stage of the disease is an important determinant of therapy and prognosis. Clinical Course,Clinical Progression,Disease Exacerbation,Exacerbation, Disease,Progression, Clinical,Progression, Disease
D018482 Muscle, Skeletal A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles. Anterior Tibial Muscle,Gastrocnemius Muscle,Muscle, Voluntary,Plantaris Muscle,Skeletal Muscle,Soleus Muscle,Muscle, Anterior Tibial,Muscle, Gastrocnemius,Muscle, Plantaris,Muscle, Soleus,Muscles, Skeletal,Muscles, Voluntary,Skeletal Muscles,Tibial Muscle, Anterior,Voluntary Muscle,Voluntary Muscles

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