Multi-electrode electromyography: developing electrical cross-sectional imaging of skeletal muscle.

Needle electromyography (EMG) is an essential diagnostic test in the investigation of patients with peripheral nerve and muscle disease. For conditions such as motor neuron disease, a relentlessly progressive degeneration of the motor system, it is the only diagnostic test available. However, current EMG technology has barely advanced in the past 50 years.
EMG involves inserting a metal needle through the skin into a muscle, and recording the electrical activity produced by the muscle fibres. Diseases affecting the motor nerves or the muscle produce characteristic changes in this electrical activity. The signal is recorded from a single point at the needle tip, and herein lies the fundamental limitation of current technology. Since only a single recording surface is used, this 'single channel' recording consists of overlapping electrical signals from dozens of individual muscle fibres, and untangling these to work out how the muscle fibres are arranged within the muscle can be difficult. Furthermore, the volume of muscle sampled is tiny, meaning that in order to diagnose a widespread disease, such as motor neuron disease, the needle has to be repositioned several times within several muscles. This increases the pain for the patient and means that some studies can take over an hour to perform.
Our proposal is to adapt and develop existing microfabrication techniques to produce a novel EMG electrode, of similar diameter to a conventional needle, which will record simultaneously from 64 points along the needle. This will allow the rapid and accurate localisation of each individual muscle fibre within the muscle without the need for needle movement, in effect producing an electrical cross-sectional image of the muscle. This will massively increase the accuracy of the test and significantly reduce the time taken.
Our group consists of clinicians and basic scientists based within the Royal Victoria Infirmary, Newcastle and Newcastle University. We have already developed multi-electrodes for recording electrical activity from within the brain, using microfabrication facilities within Newcastle University. We will adapt these to record from human muscle, and will test these in human volunteers. We also have extensive experience in developing novel software to analyse the data from multi-channel recordings, and we will develop a suite of programs to display muscle structure and function in real-time. This will allow clinicians to view the results as they are collected allowing them to decide whether a diagnosis has been reached or if further muscles need to be studied.
Our ultimate aim is to develop a prototype clinically applicable system which we will then develop in partnership with a commercial medical instrument company.
There are approximately 100,000 EMGs performed each year in the UK. Even if our system reduces the time taken by ten minutes each, this will have a massive cost saving for the NHS, quite apart from the benefits to patients in terms of improved diagnosis and reduced discomfort. We believe that this technique is achievable, and will be as revolutionary for EMG as the development of magnetic resonance imaging has been for radiology.

Basic scientists: Our understanding of human motor unit structure is largely extrapolated from animal studies. Our technique will provide the first detailed information on human motor unit structure, number and distribution.
Patients: Although we have used motor neuron disease to illustrate the potential benefits of multichannel-EMG, the benefits extend to all patients with neuromuscular disease. Needle EMG is inevitably uncomfortable. Patients experience pain as the needle is inserted through the skin, and at each subsequent movement of the needle within the muscle. Our multi-EMG needles will be of the same diameter as conventional needles, and sampling from entire motor units simultaneously will reduce the number of skin insertions and the movement within the muscle, both speeding the process of data gathering and reducing discomfort.
NHS: Cost: Current EMG needles cost approximately £5 each. We believe that disposable multi-EMG manufacture on an industrial scale would be of comparable cost. In our department alone we perform approximately 3000 EMGs per year. These take approximately 40 minutes per patient, significantly longer for complex cases such as motor neuron disease or myasthenia gravis. We estimate that multi-EMG would be beneficial in half of these examinations. Even if our technique reduces the time taken by only 20 minutes this equates to a saving of (500 hours x £200 per hour consultant time) ie £100,000 per year for our department alone. By extrapolation, this could save the NHS approximately £2 million per year given the total number of neurophysiologists in the UK. Worldwide these figures would be an order of magnitude higher.
Diagnostic accuracy: Prompt and accurate diagnosis is enshrined in the NHS patients' charter. Conventional EMG shows poor sensitivity and specificity for many neuromuscular disorders. For motor neuron disease, sensitivity is approximately 60%, and patients can require repeated EMG examinations to establish the diagnosis. Delayed diagnosis increases costs, excludes patients from the early instigation of potentially life-prolonging therapy, and exposes the patient to inappropriate additional investigations and therapies. The increased diagnostic accuracy of multi-EMG will reduce costs to both patients and the NHS.
Time scale: We aim to produce a working prototype within 3 years. We anticipate a further 3 years for commercialisation of the product, CE marking, and a further year for initial clinical trials. The benefits for the NHS will accrue from this point; immediate benefits in terms of reduced time needed for the test, and long term benefits of earlier diagnosis and instigation of life improving treatment.
Medical diagnostic companies: The UK has a strong medical technology and diagnostics sector, with over 3,000 companies and over 55,000 employees. New technology is central to maintaining this industry's world-wide competitiveness. Many peripheral nerve and muscle diseases are more prevalent in the elderly, and diagnostic technology in this age group is a growth area.