The term “radic” is Latin for root. “pathy” means something wrong. Literally interpreted, this means something is wrong with the nerve root. By itself, the term radiculopathy does not provide a cause for the nerve root injury.
The most common causes of nerve root injuries include disc herniations, osteoarthritis, trauma and diabetes. It is often misunderstood that a nerve root must be compressed by a disc herniation (rupture) in order to cause pain. There is also a misunderstanding that the compression of the nerve root is the major cause of pain.
There is an intense inflammatory chemical reaction with a disc herniation. This chemical inflammatory response is the most significant cause of nerve root pain. Of course, mechanical compression on a nerve root by disc material or by osteoarthritis can cause nerve root injury or symptoms also.
Trauma, such as a rear-ended motor vehicle accident, can also cause a radiculopathy, more commonly in the neck. A cervical spine MRI may well be normal, in some instances, due to the fact that the only fact there is compression is when one vehicle is impacting another and the person’s neck is hyperextended (bent backward compressing the nerve root). This can cause a one time crush injury to the nerve root without the person having suffered a disc herniation. Also, diabetes causes a microvasculitis which means that it adversely affects small blood vessels. Some small blood vessel endings go to small nerve root endings. A person with a normal spine MRI with a medical history of diabetes but with a clinically significant radiculopathy is believed to be suffering from a non-compressive diabetic-related radiculitis (nerve root inflammation).
For teaching purposes, please note that pain is referred. Pain does not radiate. Sensory symptoms can radiate along the skin. For example, a person with a right S1 radiculopathy will have pain referred into muscles that are innervated by the right S1 nerve root. This most often means that there are complaints of pain in the right buttock, right posterior (back) thigh and right posterior leg (calf). Pain referred into a specific nerve root distribution or map is known as a myotome. The calf would be part of the S1 myotome.
The term dermatome refers to the sensory mapping of the skin for a particular nerve root from the spine. For example, the C6 nerve root in the neck is responsible for providing sensation on the lateral (outer) aspect of the forearm and into the thumb and index finger. The C7 nerve root supplies the sensation to the long finger. The C8 nerve root supplies sensation to the medial (inner) aspect of the hand including the small finger and ring finger.
Muscle stretch reflexes (inappropriately referred to as deep tendon reflexes because the reflex mechanism is within the muscle-not the tendon) are also useful for diagnosing radiculopathies. A muscle stretch reflex is either diminished or absent in a patient with a radiculopathy. The common muscle stretch reflexes and their neurologic level include the biceps (C6), triceps (C7), patellar (L4), medial hamstring (L5) and Achilles (S1).
In addition to the clinical history of pain referred in a specific myotome, a sensory disturbance in a particular dermatome and a diminished or absent muscle stretch reflex, weakness may be present in a specific myotomal distribution also as part of the clinical examination of a radiculopathy.
In terms of additional physical examination findings, a straight leg raise test is interpreted as positive for radicular pain if it is referred distal to the knee (i.e., between the knee and ankle joint) in a specific myotomal distribution. For example, the L5 nerve root would refer pain to the shin area and the S1 nerve root would refer pain to the calf area. The analogous test for the upper limb is the Spurling maneuver which can refer pain into the upper limb in a specific nerve root distribution. The C7 nerve root will commonly refer pain to the scapula (shoulder blade) and the triceps. The C6 nerve root will frequently have a Spurling maneuver refer pain into the elbow flexors, including the biceps muscle, as well as the scapular region.
A radiculopathy can be confirmed objectively via electrophysiologic testing, namely an EMG needle examination performed by a qualified physician, such as one with training in physical medicine and rehabilitation. Physical Medicine and Rehabilitation is the only specialty accredited by the American Board of Medical Specialties with required training in electrodiagnostic medicine as part of the formal training and board certification process. In addition, according to The AMA Guides to the Evaluation of Permanent Impairment, electrodiagnostic testing is considered a more important and objective differentiator of impairment beyond that of physical examination findings. Such testing is very useful in cases of radiculopathies and carpal tunnel syndrome.