Study Of Electromyography And Somatosensory Evoked Potentials In Neuralgic Amyotrophy

Neuralgic amyotrophy(NA) is a neuromuscular syndrome and the lesions mainly locate in brachial plexus. The typical clinical manifestations include shoulder and(or)upper extremity pain, followed by weakness, muscle atrophy and sensory impairments. Specific pathogenesis of the disease is not yet clear, and may be associated with infection or immune-mediated. Involved nerve biopsy confirmed the presence of axonal degeneration. Routine laboratory tests are usually normal. The clinical diagnosis depends on the patient’s history, clinical manifestations and EMG.EMG is very important to diagnosis and differential diagnosis of the disase..Objective:To probe into the characteristics of clinical manifestation and electrophysiology in NA and to analyze the diagnostic value of electromyography and somatosensory evoked potential so as to provide the objective electrophysiological evidence for early diagnosis of NA.Methods:We studied 25 cases with NA and 25 normal controls. Electromyogram was measured with the Nicolet myoelectric/evoked potential instrument.1. Electroneurography and F-wave measured: The recording electrode was placed over the muscle belly and the reference electrode was placed distally over the muscle tendon. The stimulating electrode was placed over the nerve with the cathode close to the recording electrode and the nerve was stimulated. CMAP was recorded with surface disc electrode and its latency and amplitude was analyzed. The F-wave latencies were obtained by stimulating the distal portion of the median and ulnar nerves using motor nerve conduction setups. SNAP were recorded by stimulation of the distal sensory fibers in the orthodromic sensory conduction test with the recording electrode placed close to the stimulator and its amplitude and SCV were analyzed.2. Needle electrode electromyography measured: local skin disinfection, using concentric needle electrodes for recording and the checked muscle penetrated fast.Recording was made from the checked muscle in relaxed state, slight and strong contraction.3. Somatosensory evoked potentials measured: reference to the international 10-20 EEG electrode placement system to place scalp electrode. Recording electrodes placed on Erb’s point(supraclavicular fossa), 7th cervical and contralateral stimulation C3 ’or C4’ zone, and the reference electrode placed on FPz.Results:1. When stimulated at Erb’s point, compared with their healthy side, the motor latency of musculocutaneous nerve slightly longer(P<0.05). Compared with the healthy control group, the axillary nerve, musculocutaneous nerve, and median nerve motor latency prolongation were statistically significant(P<0.05).2. When stimulated at Erb’s point, compared with their healthy side, axillary nerve,musculocutaneous nerve CMAP amplitudes were significantly reduced in the affected side of the case group(P<0.05). Compared with the healthy control group, in the affected side of the case group axillary nerve, musculocutaneous nerve, median nerve,ulnar nerve, and radial nerve CMAPs amplitudes were significantly reduced.(P<0.05).3. When stimulated at wrist, whether compared with their healthy side or healthy control group, distal motor latency, MCV, SCV, CMAPs and SNAPs amplitudes of median nerve, ulnar nerve were abnormal mildly, F-wave latency of median nerve and ulnar nerve prolonged slightly, but the above changes were not statistically significant(P>0.05).4. Spontaneous potential occurrence rate, the duration and amplitude of MUPs in deltoid were statistically significant(P<0.05). While the above observed indicators in abductor pollicis brevis were no statistical significance(P>0.05).5. Bilateral stimulation of the median nerve respectively, compared with the contralateral, in affected side of patient group N9 amplitude reduced, N13 latency prolonged, N9-N13 peak interval prolonged, the changes were statistically significant(P<0.05). Compared with the healthy control group, the patient group N9, N13 amplitude reduced, N9, N13, N20 latencies prolonged, N9-N13 peak interval prolonged, all changes were statistically significant(P<0.05).Conclusion:1. In the affected side of case group, axillary nerve, musculocutaneous nerve CMAPs amplitude were significantly reduced, motor latencies were slightly prolonged, and deltoid EMG were typical neurogenic damage, suggesting NA often involed proximal nerves, and the pathological change of motor nerve fiber might be axonal degeneration.2. In the affected side of case group, ulnar nerve SNAP amplitude reduction and SCV slowing slightly, suggesting sensory nerve involvement in NA was also mainly axonal damage and lesions were located in the distal spinal ganglion.3. In SEP, N9 amplitude reduction, N9-N13 peak interval prolongation indicated deep sensory conduction fibers NA were involved, and lesion segments may exist mild demyelination.4. The abnormal rate of MCV, SCV, F-wave, EMG and SEP were different in NA patients.5. For NA patients, bilateral electrophysiological examination can found relatively abnormal of electrophysiological indicators, thereby enhancing the positive rate of electrophysiological diagnosis and helping diagnosis of the early or mild NA patients.