Characteristics of giant F-waves in amyotrophic lateral sclerosis

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Objective To investigate the characteristics of giant F-waves in patients with amyotrophic lateral sclerosis (ALS) and the relationship between giant F-waves and disease phenotype. Methods Motor nerve conduction study and F-waves were performed to the median, ulnar, tibial and peroneal nerves of 55 patients with ALS and 52 healthy volunteers. A series of 100 electrical stimuli were employed to obtain F-waves. The following F-wave variables were estimated: frequency of giant F-waves, frequency of patients with giant F-waves, the relationship between giant F-waves and lower motor neuron dysfunction, the relationship between giant F-waves and upper motor neuron dysfunction, the relationship between giant F-waves and disease duration, the relationship between giant F-waves and disease severity, and the relationship between giant F-waves and disease progression rate (DPR). Results The frequencies of giant F-waves (ALS: median nerve 0.00(0.00)%, ulnar nerve 0.00(1.02)%, tibial nerve 0.00(0.00)%, peroneal nerve 0.00(0.00)%. Normal controls: median nerve 0.00(0.00)%, Z=-2.360, P=0.018; ulnar nerve 0.00(0.00)%, Z=-3.997, P<0.01; tibial nerve 0.00(0.00)%, Z=-3.006, P=0.003; peroneal nerve 0.00(0.00)%, Z=-3.006, P=0.003) and the frequencies of patients with giant F-waves (ALS: median nerve 13/55, 23.6%, ulnar nerve 26/55, 47.2%, tibial nerve 18/55, 32.7%, peroneal nerve 16/55, 29.1%. Normal controls: median nerve 4/52, 7.7%, χ2=0.024, P=0.024; ulnar nerve 7/52, 13.5%, χ2=14.326, P<0.01; tibial nerve 6/52, 11.5%, χ2=6.897, P=0.009; peroneal nerve 6/52, 11.5%, χ2=5.042, P=0.025) in the median nerve, ulnar nerve, tibial nerve and peroneal nerve were significantly increased compared with those of the normal controls. No significant differences were found in the frequencies of upper motor neuron dysfunction between nerves with giant F-waves and nerves without giant F-waves in the median nerves, ulnar nerves, tibial nerves and peroneal nerves of ALS patients. The compound muscle action potential amplitude of nerves with giant F-waves was significantly higher than those of nerves without giant F-waves in the median nerves (11.20(5.80) mV vs 5.90(8.50) mV, t=2.883, P=0.004)and tibial nerves ((13.20±4.61) mV vs (10.69±4.76) mV, t=-2.222, P=0.028)of the ALS patients. No significant correlation was detected between the frequency of giant F-waves and disease duration or ALS functional rating scale in the ALS patients, while the frequency of giant F-waves correlated inversely with the DPR(r=-0.287, P=0.034). No significant differences were detected in disease duration between ALS patients with giant F-waves and those without giant F-waves. Compared with those in ALS patients without giant F-waves, the revised ALS Functional Rating Scale score (37.00(3.00) vs 42.00(4.75), Z=3.197, P=0.001) was more, the DPR (0.50(0.35)vs 0.90(0.43), Z=-3.033, P=0.002) was slower in ALS patients with giant F-waves. Conclusions The giant F-waves were significantly increased in the ALS patients than those in the healthy volunteers and were distributed asymmetrically between the left and right sides. These electrophysiological characteristics of ALS patients fitted well with progressive loss of anterior horn cells, and indicated differential involvement of different spinal motoneuron pools in the ALS patients. No correlations were found between the frequency of giant F-waves and disease duration. The appearance of giant F-waves may indicate loss of spinal motoneuron early in the disease course, and may suggest that the degree of reinnervation and functional compensation are relatively good after motoneuron loss. Key words: Amyotrophic lateral sclerosis; Neural conduction; F-wave