F wave study in amyotrophic lateral sclerosis: assessment of balance between upper and lower motor neuron involvement.

Objective: We sought to record significant F wave variable changes in ALS patients having no advanced disease. Furthermore, an interpretation of these F wave abnormalities in the context of upper (UMN) and lower motor neuron (LMN) dysfunction was attempted.

Methods: Standard motor and sensory conduction study was performed to the ulnar nerves of 23 patients with ALS (13 males and 10 females with mean age 67.2+/-5.3 years), having a clinically predominant LMN syndrome. A series of 40 electrical stimuli were also delivered to both their ulnar nerves in order to obtain F waves. The following F wave variables were estimated: F persistence, F wave latency, amplitude, duration and F chronodispersion. Twenty-three, age-and gender-matched healthy volunteers served as controls.

Results: Both the distal and proximal ulnar a-CMAPs (P=0.001) and the MCV (P=0.014) values were significantly decreased in patients, than the controls. The sensory conduction study was normal. The ulnar F wave persistence in the ALS patients was significantly lower than that of the controls (P=0.0007). The mean (P=0.0001), minimal (P=0.0001) and maximal (P=0.0001) F wave latencies were significantly prolonged, the F wave amplitudes (P=0.0001) were significantly higher and the F wave chronodispersion (P=0.014) was significantly increased in the patients than the controls.

Conclusions: Significant F wave abnormalities occur in patients with ALS, even those patients having no advanced disease. Increased F wave amplitudes combined with low persistence is a pattern consistent with ALS. Conclusions: Our results show that patients with ALS having predominantly LMN involvement also have electrophysiological UMN dysfunction.