What is the diagnosis of Motor Neuron Diseases?

By  ,  National Institute of Health
Jan 07, 2013

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There are no specific tests to diagnose MNDs. Symptoms may vary among individuals and, in the early stages of the disease, may be similar to those of other diseases, making diagnosis difficult. A physical exam should be followed by a thorough neurological exam. The neurological exam will assess motor and sensory skills, nerve function, hearing and speech, vision, coordination and balance, mental status, and changes in mood or behavior.

Tests to rule out other diseases or to measure muscle involvement may include the following:

Electromyography (EMG) is used to diagnose muscle and nerve dysfunction and spinal cord disease. It is also used to measure the speed at which impulses travel along a particular nerve. EMG records the electrical activity from the brain and/or spinal cord to a peripheral nerve root (found in the arms and legs) that controls muscles during contraction and at rest. Very fine wire electrodes are inserted one at a time into a muscle to assess changes in electrical voltage that occur during movement and when the muscle is at rest. The electrodes are attached to a recording instrument. Testing usually lasts about an hour or more, depending on the number of muscles and nerves to be tested.


EMG is usually done in conjunction with a nerve conduction velocity study. This procedure also measures electrical energy to test the nerve's ability to send a signal. A technician tapes two sets of flat electrodes on the skin over the muscles. The first set of electrodes is used to send small pulses of electricity (similar to a jolt from static electricity) to stimulate the nerve that directs a particular muscle. The second set of electrodes transmits the responding electrical signal to a recording machine. The physician then reviews the response to verify any nerve damage or muscle disease.

Laboratory screening tests of blood, urine, or other substances can rule out muscle diseases and other disorders that may have symptoms similar to those of MND. For example, analysis of the fluid that surrounds the brain and spinal cord can detect a number of disorders, including PPS. Blood tests may be ordered to measure levels of the protein creatine kinase (which is needed for the chemical reactions that produce energy for muscle contractions); high levels may help diagnose muscle diseases such as muscular dystrophy.


Magnetic resonance imaging (MRI) uses computer-generated radio waves and a powerful magnetic field to produce detailed images of body structures including tissues, organs, bones, and nerves. These images can help diagnose brain and spinal cord tumors, eye disease, inflammation, infection, and vascular irregularities that may lead to stroke. MRI can also detect and monitor degenerative disorders such as multiple sclerosis and can document brain injury from trauma. MRI is often used to rule out diseases other than the MNDs that affect the head, neck, and spinal cord.


Muscle or nerve biopsy can help confirm nerve disease and nerve regeneration. A small sample of the muscle or nerve is removed under local anesthetic and studied under a microscope. The sample may be removed either surgically, through a slit made in the skin, or by needle biopsy, in which a thin hollow needle is inserted through the skin and into the muscle. A small piece of muscle remains in the hollow needle when it is removed from the body. Although this test can provide valuable information about the degree of damage, it is an invasive procedure that may itself cause neuropathic side effects. Many experts do not believe that a biopsy is always needed for diagnosis.


Transcranial magnetic stimulation was first developed ...

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