How can neuromuscular diseases be investigated?
The first stage in the investigation of neuromuscular diseases involves eliminating diseases somewhere else in the body which may have an indirect effect on the function of the neuromuscular system. This may include doing a complete blood profile (including blood tests for hormonal and infectious diseases), X-rays of the chest and abdomen, as well as an abdominal ultrasound. If it’s suspected that an animal may have a disease which affects the junction between the nerves and muscles, such as Myasthenia Gravis, a blood test which looks for antibodies directed toward the acetylcholine receptor (anti-AChR antibody titre) may be considered.
Other tests to re-enforce the suspicion of Myasthenia Gravis include a ‘Tensilon test’. In this test a short-acting antidote to Myasthenia Gravis (Tensilon) is injected into a vein. In affected animals there will be a dramatic increase in muscle strength immediately after injection and collapsed animals may get up and run about. However, the effects will wear off after a few minutes.
A spinal tap is often considered at this stage of the investigation to look for inflammation of the root of the nerve (polyradiculoneuritis).
Finally, another test that can be used, not to identify the cause of a neuromuscular disorder but to confirm that we are looking at the right part of the nervous system, is an electromyogram (EMG). An EMG machine can be used to deliver a small electrical stimulation to an individual nerve or muscle in an anaesthetised animal. Using an EMG machine a vet can evaluate how well the muscles respond to stimulation from the nerves.
If the above preliminary tests fail to identify a cause, the next step is to take a biopsy of the nerve and muscle to determine if the problem is an inflammation or a degeneration of the nerve or muscle. This degeneration can be transient and of unknown origin (such as distal denervating disease or chronic relapsing demyelinating neuropathy), while others may be permanent and slowly progressive (inherited neuropathy or myopathy such as muscular dystrophy).