Breaking the loop: “Causalgia”

What if you were recovering from knee replacement surgery and you are just sitting comfortably, knitting, when you feel the outer side of your new knee burst into flame?

You touch it to see if it is actually hot and a searing pain hits your cerebrum like a bolt of lightning. The lightest of contact, even tangentially, produces excruciating attacks of caustic pain. And it never gets better.

This is Florence’s story  – the patient we met in the last issue (October, 2019). I pegged her situation as a likely case of causalgia, also known as Complex Regional Pain Syndrome (CRPS).

Typically, there is a history of pain in a limb or a smaller part of a limb (as in Florence’s case, the anterior femoral cutaneous nerve.) This pain is characteristically a burning pain and it is much worse than one would expect under the circumstances. The term allodynia applies, meaning that an otherwise normal stimulus produces pain that is wildly out of proportion to the situation.

The symptoms of CRPS are often constant but can present with a pattern of relative inactivity punctuated by spikes of pain that are triggered by certain things like movement, light touch, hot or cold, vibration, a breeze or a feather. Some cases are relatively mild and recover spontaneously. Most cases are bad and never completely go away. Rarely, the pain worsens over time and spreads, consuming an ever-increasing area, or even developing in the same part on the opposite side of the body. It can affect people of any age, but it is almost never seen in very young children and is uncommon in the elderly. Women are more likely to be affected than men. But the fact is, CRPS is a rather uncommon disorder across any population. Many primary healthcare providers have never even seen a case.

On physical examination of the affected region you will first be looking for changes to the skin:

• Is the colour normal? Is it pale, or are there blotches of red or blue or purple?
• Is the temperature normal? You may note that the painful spot of skin or the entire limb is warmer or colder than other parts.
• Does the skin seem at all sweaty or damp?
• Do you see any textural changes such as abnormally smooth and shiny areas or mottled patches of epidermal sloughing?

When limbs or digits are involved, active range of motion of joints may be restricted; passive ROM’s can also be affected and the limitations are often in all directions.There can be weakness on resisted testing and trouble coordinating movements. Fine tremors are not uncommon.

There is a general understanding in medical texts that all of the features of CRPS are ultimately due to abnormal microcirculation of fluids and nutrients, and that this is due to “nerve damage,” without elaborating on what’s meant by the word “damage.” The word indicates a breakage of structure, a disruption of the integrity of the physical substance of a thing. And if “the thing” we are talking about is a living cell, or a collection of cells (ie. tissues), we know that when these structures break and their integrity is compromised, they will be replaced (ideally) by new cells that work in the same way.

CRPS is not about damage to the structure, it is a case of damage to the function – the way the cells/tissues, structured as they are, are working. If things are to be made and moved, you have to have a way to control just what work is done, and when.

Enter the humble reflex arc, AKA the feedback loop. Mechanoreceptors detect stretch, pressure and hair movement – all of the elements of the sense of touch. Nociceptors and thermoreceptors respond to local changes in chemistry and temperature. For the fast pain receptors (A-delta), a single action potential (AP) produces a conscious sense of sharp, prickly pain. One AP from a slow (C-type) sensory nerve is not perceived, while a volley of AP’s down these unmyelinated fibres results in a sense of intolerable pain. The former tell us about the time and location of the injury, the latter define its extent.

The motor nerves to the skin are predominately (if not exclusively) sympathetic motor fibres. These efferent autonomic nerves release signaling chemicals – neurotransmitters/vasoactive amines, which instigate action in target tissues such as muscle and glands (sweat/sebaceous).

When action is initiated by increased sympathetic motor activity, observable things happen: Smooth muscle cells contract to make hair stand on end or blood vessels constrict; adventitial cells which envelope the capillaries act to alter the permeability of the vascular beds; glands are stimulated to increase synthetic and secretory functions.

Afferent signals from nociceptors (fast and slow) and mechanoreceptors are linked via the central nervous system (in simple or not-so-simple ways) to sympathetic efferents which signal the effector tissues (smooth muscle cells, glands, adventitia) to act. Depending on the location of the sensors and the type of effector involved in the motor response, we can describe reflex loops as somato-somatic, viscero-visceral, somato-visceral and viscero-somatic.

A vast majority of reflex/feedback loops are of the negative type. There are only a few examples of positive feedback loops. When the end product incites more action and the system spirals into a self-perpetuating cycle, things can become extreme. (Like the way hyperthermia becomes heat stroke: the warmer the room, the more the vasculature to the skin opens up to dissipate excessive body heat, but the blood picks up more heat, the skin flushes even more and body temperature will rise to fatal levels without treatment.)

And this, I propose, is the nature of CRPS – a somato-visceral reflex loop that is stuck and self-perpetuating. With reflex loops, it can be difficult to know which came first – the painful stimulus or the hyperactivity of the sympathetic motor system – but the results are obvious. Whatever the primary lesion (and there are times when none can be identified) – be it a broken ankle or shoulder bursitis or surgery – we often see immobilization of the area, spontaneously because it hurts or deliberately because it is necessary. Perhaps it requires a physiologic pre-disposition, plus some stressful circumstances and some kind of ‘perfect storm’ of conditions, but there is an uptick in sympathetic nervous system activity.

When sympathetic activity is turned up too high, the effects are felt throughout the involved tissues. Increasing sympathetic motor impulses causes vasoconstriction of arterioles, which produces ischemia and, simultaneously, makes the capillary beds more permeable. This “leakiness” affects the interstitial fluid compartment and impairs movements of nutrients and wastes, which explains the coolness and colour changes and altered texture that we can see. The dampness of the skin is because of increased motor messages to sweat glands.

The effect on peripheral sensory receptors is to exaggerate their sensitivity. The threshold of firing is lowered so they report a greater intensity of stimulus than is actually occurring. These effects can be local, regional or segmental. The process of sensitization not only affects the sensory receptors of the periphery, it happens centrally as well.  Layers of integration and influence are provided by the brain and spinal cord essentially creating dysfunctional reflex loops that can be highly complicated. These facts reveal possible ways to help a patient like Florence. In order to stop a cycle of sensory-motor activity that is stuck in a self-perpetuating loop, we must interrupt it – break the loop.

The most common medical treatment is pharmaceuticals to dampen the pain messages and relieve associated insomnia. The most radical medical approach is a sympathectomy – where the affected motor nerves/ganglia are disconnected surgically or chemically. While pain management strategies can be helpful, if it can be done, fixing the source of the pain has to be the most sensible approach.

Amongst a list of many possible contributors in painful conditions, Dr. Claraco provides some insight for us: “a lack of sufficient non-noxious information from segments related to the kinetic chain – including proximal and distal joints, synergistic and antagonistic muscles.” This includes information on stretch, pressure, temperature, vibration and movement in general. We need to provide these kinds of non-painful stimuli in order to change sympathetic motor output by changing the sensory input.

Chiropractic care for a patient like Florence with CRPS could include:

• Adjustments of areas of the spine and extremities where joint play has been compromised
• Joint mobilization – passive ranges of motion with gradual increase to the range and speed of the movements; intermittent distraction
• Strain/counterstrain – positional release techniques can reset muscle spindles to restore better patterns of movement across related (and even remote) joints
• TENS/IFC/neurostimulation to disrupt locked-in sensory-motor loops
• Exercise – graded, from assisted active movements to resistance training, in order to improve function

Collaboration with other hands-on professionals may be in order.

If you ever get a chance to help a patient with CRPS, make sure to properly document the specifics of their case. The use of Patient-Based Outcomes Assessment Instruments, such as the McGill Pain Questionnaire is highly recommended if you want to objectively assess the effectiveness of treatment. You must have them complete the form before you provide any care and then again at regular intervals over the planned course of visits.

For Florence, her back spasms cleared up when she changed her bed. I didn’t get the opportunity to treat her at all. She is still trying different pain medications; after four long years she finally has an appointment with a pain specialist. She continues to endure, stoic as ever and utterly devoted to care for her husband as best she can, in spite of her crazy knee pain.

Sometimes the cases we see – even if they don’t work out as anticipated – can inspire us to review our understanding of the nature of pain and give us hope that what we do can help.

DR. DAWN ARMSTRONG is a graduate of CMCC and has been in practice for over 30 years. She is currently focused on promoting life-long learning and professional development and has created a continuing education course – Clinical Record Keeping: A Hands-On Approach. Learn more at auroraeducationservices.ca.