Utility of Dissociated Intrinsic Hand Muscle Atrophy in the Diagnosis of Amyotrophic Lateral Sclerosis

The overall goal of the following experiment is to obtain the split hand index, a simple neurophysiological measurement, which reliably distinguishes a Myotrophic lateral sclerosis or a LS from mimic neuromuscular disorders. This is achieved by first selecting appropriate patients via their history and through a neurophysiological examination as a second step. The maximal motor responses are recorded from three intrinsic hand muscles, namely the abductor lysis previs, or A PB first dorsal interosseous or FDI and abductor digi Mimi or A DM.Next, the product of the compound Muscle Action Potential or CMAP recorded for the A PB and FDI is divided by the cmap recorded for the A DM.In order to obtain the split hand index, the results reveal that a diagnostic cutoff value of 5.2 for the split hand index reliably differentiates a LS from mimic neuromuscular disorders.

Well, the main advantage of this technique is its ease and simplicity of use. To begin determine the suitability of AM Myotrophic lateral Sclerosis or a LS patients for testing by selecting patients who have been diagnosed with a LS or a neuromuscular disorder. Exclude patients with coexistent focal neuropathy, median neuropathy at the wrist, ulnar neuropathy at the elbow, or patients with a generalized neuropathy such as diabetic polyneuropathy.

Next, confirm the diagnosis of a LS or neuromuscular mimic disorders, and ensure all patients provide informed consent for all of the neurophysiological procedures. Calculate the rate of disease progression in all A LS patients according to the formula shown here. Then determine muscle strength in all patients using the Medical Research Council or MRC rating scale and develop a total MRC score comprising of upper limb and lower limb muscle groups.

The total MRC score of normal muscle strength should be 90 no. Begin the assessment by performing motor nerve conduction studies on the median and ulnar nerves with compound muscle action potential responses or cmap responses recorded from the abductor lysis brevis or A PB, the first dorsal interosseous or FDI and the abductor digi minimize or a DM First, clean the skin surface over each muscle and the wrist with an abrasive gel to reduce skin resistance and an alcohol wipe to improve adhesion. Then apply conductive gel to the electrodes and position 10 millimeter gold disc electrodes in a belly tendon arrangement over each muscle.

Position the active electrode over the midpoint of the respective muscle, ensuring a negative takeoff of the cmap response, and position the reference electrode over the base of the thumb for a PB and FDI cmap recordings and the base of digit five for a DM cmap recordings. Set the distance between the stimulating cathode and active electrode for a PB and a DM compound motor action potential responses to five centimeters and the distance to the FDI at 14 centimeters. Next, prepare the neutral Earth site by scrubbing the dorsal aspect of the hand with an abrasive gel to reduce skin resistance.

Then clean the site with an alcohol wipe. Position the Electrosurgical neutral Earth plate between the stimulating and G one electrode with conductive gel. Set the filter between three hertz and 10 kilohertz and set the sweep speed to 20 milliseconds.

Then ensure that the sensitivity for recording cmap responses is set to five millivolts. Monitor the temperature at the site of stimulation throughout the study and make sure that the limb temperature is maintained at 32 degrees Celsius. Slowly increase the stimulus intensity to ensure that the selected site exhibits the lowest threshold for stimulation to avoid volume conduction.

Then set the stimulating current to 20%above the super maximal current, which is the intensity required to produce a maximal cmap response. To begin analysis, measure baseline to peak cmap amplitudes over the A-P-B-F-D-I and a DM muscles in a LS patients and the neuromuscular mimic disease controls. Next, calculate the split hand index by multiplying the cmap amplitude recorded over the A PB and FDI muscles and dividing the product by the cmap amplitude recorded over the A DM muscle.

Then compare the split hand index between a LS patients and neuromuscular mimic disorder pathological controls according to the standards for reporting diagnostic accuracy. In order to determine the diagnostic utility of the split hand index, determine optimal diagnostic cutoff values for the split hand index by using the receiver operating characteristic or ROC curves then derive the ROC curve by plotting the sensitivity and one specificity for split hand index values derived from a LS and neuromuscular disorder patients. In total 44 patients were studied upon combining the cmap p amplitudes.

It was evident that there was a significant reduction of the split hand index in a LS patients compared to neuromuscular disorder patients. While this reduction in the split hand index was a ubiquitous finding in a LS, it was most pronounced in a LS patients with limb onset disease. The split hand index robustly differentiated a LS from neuromuscular disorder patients with an optimal diagnostic cutoff value of 5.2 as indicated by the dotted black lines.

Importantly, the diagnostic utility of the split hand index was greater in a LS patients with limb onset disease. After watching this video, you'll have a good idea of how to calculate the split hand index by recording maximal motor responses from the A-P-B-F-D-I and a DM muscles in the hand. Measurement of the split hand index helps to differentiate a LS from neuromuscular mimic disorders.