New biomarkers for motor neurone disease are required to improve diagnosis and facilitate clinical trials. While significant progress has been made in developing limb function biomarkers there has been far less attention on bulbar disease. Electrical impedance spectroscopy uses imperceptible electrical currents to examine the health of muscle. Previous studies have used simple planar electrode arrays to compare healthy volunteers to motor neuron disease patients. In the present study we test the hypothesis that a more complex, 3-dimensional electrode arrangement will provide a greater interrogation of the intricate tongue musculature.

Methods:

A custom made eight electrode electrical impedance spectroscopy device was built, utilising a range of input frequencies and employing 12 electrode configurations. Impedance spectroscopy measurements were undertaken on 20 healthy volunteers and 23 motor neurone disease patients with bulbar disease. The patients fulfilled in the Awaji-Shima diagnostic criteria. Bulbar disease was determined by either reported symptoms, clinical examination or EMG. Reliability was assessed through the intraclass correlation coefficient. Standard descriptive statistics, include Mann-Whitney testing between the two groups were determined.

Results

There were no significant differences in the demographics of the volunteer and patient groups (p>0.05). The pooled intraclass coefficient was 0.87. Significant differences in impedance measurements were observed between volunteers and patients across multiple input frequencies and electrode configurations (p<0.01). Comparison of 2- and 3-dimensional electrode configurations demonstrated that 3-dimensional configurations were more likely to yield a significant difference (p<0.05). Patients found the recordings easy to tolerate and more comfortable than standard EMG.

Conclusion

Our novel impedance system shows potential for the detection of bulbar lower motor neurone pathology in motor neurone disease. 3-dimensional electrode configurations improve detection of differences between volunteers and patients. The approach could augment the diagnostic process and provide a much needed quantitative measure of tongue muscle health for clinical trials.