Neurological Testing for Herniated Disc
Herniated discs are usually painful, and they can cause changes in neurological function. Because of their close proximity, herniated discs often compress sensitive spinal nerves. Like crime scene clues to a detective, the findings of a neurological examination help doctors narrow down the list of suspects. Numbness, or altered sensation, muscle weakness and reflex changes can point to certain nerves that point to specific disc lesions. Specialized electrical testing can further help identify the location and severity of the herniation.
Nerves that travel from the spinal cord to the rest of the body are organized like trees, with roots, trunks and branches and almost the same in everyone. With a disc herniation, the nerve roots are quite susceptible to compression. The specific level of the disc herniation will determine which nerve root is most vulnerable.
The location of numbness -- or other altered sensations -- can point to specific nerve roots. A February 1999 article published in "American Family Physician" describes how identifying the involved nerve root helps to implicate the likely level of a disc lesion. Doctors will often test sensation with a cotton wisp or tissue for light touch, and a pinwheel or other device to test for contrasting sharp sensations.
Just as doctors can determine the likely source of numbness by tracing the nerve back to its root, certain patterns of muscle weakness can also point to problems of particular nerve roots and the discs that may be causing the problems. Muscles may be controlled by nerves that have contributions from several roots, but certain muscles are served by nerves with 1 predominant nerve root contributor. For example, the muscle that extends the big toe is primarily served by a different nerve root than the muscles that allow you to rise up on your tiptoes. By knowing which muscles to assess, your health care provider can determine which nerve root may be in trouble.
A disc herniation may affect reflexes in the arms or legs. There are 3 common reflexes of the upper extremities and 2 in the lower extremities that are highly dependent on different nerve roots. When a particular reflex is reduced, or in some cases increased, compared to the opposite side, it provides another clue that there may be a problem at a specific level. While sensory testing requires interpretation from the patient, and muscle testing requires consistent effort from the patient, reflex testing is more objective because the response is involuntary. An astute examiner can gain a lot of information from those ankle, knee and elbow taps.
Your doctor can usually do routine sensation, strength and reflex tests, while a neurologist will usually do electrical diagnostic studies. These tests involve inserting small needles into specific places in an arm or leg. Electrical activity in the nerves and muscles can then be measured.
The two most common tests are electromyography and nerve conduction studies. Electromyography measures electrical activity within a muscle at rest and while contracted. Electrical activity within the muscle provides information about how the nerves and muscles are communicating. Nerve conduction studies measure the speed and quality of electrical signals along the course of nerves. For a surgeon or other doctor, this will help to confirm a diagnosis of herniated disc, or it will show a different condition is causing the nerve problems.
Ron Rogers, a Washington chiropractor, has worked with local and national regulatory bodies in his profession and has provided consultation to the national chiropractic licensing board. He is recognized by the National Strength and Conditioning Association as a certified strength and conditioning specialist. Rogers' works have been published in several peer-reviewed professional journals, covering topics ranging from musculoskeletal diagnosis to research-based rehabilitation strategies.