February 2002

Pulling the Plug on Pain

By Patrick De Bock, PT

Pulling the plug on Pain

The use of TENS in treating autonomic dysfunction.

The use of electrical stimulation for treating pain is common in physical therapy. Sometimes, it is more efficacious than the use of medications, and it is certainly safer.

Pain treatment is necessary due to many different indications. In the case of autonomic dysfunction, which refers to the sympathetic nervous system and can encompass symptoms such as sweating and cold extremities,¹ the symptoms are considered to be part of the pathology that causes the pain. As such, they may have been overlooked as a necessary evil of the pathology. There are, however, effective treatment techniques available. Transcutaneous electrical nerve stimulation (TENS) is believed to be efficacious in treating autonomic dysfunction.^2,3

Genesis of Autonomic Dysfunction
The relationship between pain and the autonomic nervous system is complicated. There is some evidence that, in certain pain conditions, the autonomic nervous system becomes involved in the pathology.^3-6 Anatomically, there are probably three main neurological categories in which autonomic dysfunction can take place: the central, spinal, and peripheral areas.^2,7

The processing of central autonomic activity takes place in the rostral formatio reticularis, cortex, limbic system, cerebellum, hypothalamus, and pituitary gland. The spinal part refers to the so-called "sympathetic reflex" and though the scientific value is not completely understood, in my own observations there is practical evidence for electrotherapy treatment. The peripheral area is the primary place of injury. Long-lasting, painful stimuli in joints and tendons lead to a connection that eventually involves the central and spinal areas.^2,7

Electrical stimulation for the treatment of central and peripheral autonomic dysfunction employs microcurrent, but there is also evidence supporting TENS use in treating spinal autonomic dysfunction.1,6 Which way does a painful sensation go before it reaches the brain? Sensation involves the afferent (Aa, Ab, Ad, and C) fibers. The Ad and C fibers are responsible for pain sensations. As soon as these stimuli reach the dorsal horn of the spinal cord, there are three primary results.^1-8

First, a connection to the ventral horn provokes a motor response. Second, the brain receives and analyzes the signal in order to characterize the sensation (for example, as sharp, tingling, or dull); to express its intensity (for example, light, moderate, or unbearable); and to determine its source (for example, the knee, hand, or shoulder).

Third, interneurons provide a connection with the nucleus intermediomedialis and nucleus intermediolateralis. These are the spinal sympathetic centers in the lateral horn between C8 and L2. A further connection will be made with the ventral horn in order to reach the sympathetic chain; this will eventually route the noxious stimuli to organs, sweat glands, and the muscles of the arteries.

Clinical Findings
The involvement of the autonomic nervous system in a pathological condition is probably undetectable through diagnostic testing and is not usually detected during clinical examination. Nevertheless, there are three clues to its presence: chronic pain; the symptoms noted during a thorough clinical examination; and certain well-known pathologies, such as reflex sympathetic dystrophy, adhesive capsulitis, chronic tendinitis, whiplash, and (perhaps) fibromyalgia.^1,4-11

If pain has been present for weeks or months, it is almost certain that the continued afferent activity of the Ad and C fibers will have caused peripheral, spinal, and central involvement. A good clinical examination will reveal symptoms that might otherwise be overlooked. The following symptoms sometimes indicate autonomic involvement:

• the skin shows cyanotic color, sweating, sensitivity, and decreased capillary refilling;
• the muscles show increased volume and tonus, resistance to stretching, and decreased force;
• the joints show resistance to passive motion, stiffness, and decreased range of motion;
• the periosteum shows sensitivity; and
• the nerves show pain during traction tests and are sensitive to palpation.

Table 1. Differences between somatic and autonomic innervation. Parentheses indicate that the innervation level can differ a little from person to person.1

Table 2. Settings used to apply the gate-control theory.

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