Do Common Substances — Such as Pesticides, Cosmetics and Cleaning Products — Contribute to Neuropathic Pain?

Tissue damage is an easy target for blame in the chronic pain arena; but although tissue damage may be directly or indirectly involved, it is only one of the many factors that lead to a painful, confusing presentation of symptoms.

All human experiences begin as stimulation of neural receptors by neural excitants with contributions from biomechanical, biochemical, and psychological factors, and a profoundly complex interaction between them. From pre-birth until death, the centrally mitigated nervous system is bombarded in uniquely personal ways to form learned behaviors and regulate habits of use. It can also lead to ingrained, chronic facilitation of peripheral nerves or sensitization of the central nervous system (CNS) as a whole (central sensitization).

When neural receptors are sufficiently provoked, information is transmitted along neural pathways toward the spinal cord or brain to give us sensory impressions. In turn, the CNS or the spinal cord can send back appropriate responses for any required actions.

With deep respect for the enormously complex process of neural transmission, we can most simply state that this incorporates the release of chemicals—neurotransmitters—and is dependent on a vast number of factors, including permeability, thresholds, tolerance, length and degree of sustained stimuli, cellular biochemistry, whether the stimuli is excitatory or inhibitory, and a host of others.

Environmental Stimuli

Regardless of whether the stimuli originate outside the organism (exogenous) or from within the organism (endogenous), each input can augment, diminish or distort the nervous system’s perceptions of the experience. These perceptions and associated responses are based on individual interpretation of stimuli and are influenced by emotions, memories, previously facilitated pathways, expectations and a distinctly personal combination of other factors.

These perceptions direct us to make sense of the world around us, to make moment-to-moment decisions, and to organize, categorize and interpret the data. Much of this is unconsciously generated yet absolutely necessary in order to respond to and survive amid the opportunities, chaos and dangers that surround us in daily life.

Very often—alongside a client’s apparent injury or illness—the presentation of acute or chronic pain, physical or emotional impairments, functional limitations, and a host of compensations can vastly alter the quality of life and significantly affect behavior, activities, sleep, depression, anxiety and apprehension and contribute to the use of medications.

The combination of severe pain, disability, illness or injury behavior, as well as associated psychological stressors, often drives the person from doctor to doctor, from one modality to another, and through a series of surgeries and medications in hopes of finding some element of relief. Along the path, medication interactions may produce their own bizarre presentation and addiction behaviors may cloud the picture of reality.

Our environment is filled with an infinite degree of stimuli every moment of every day. It would be overwhelming and impossible to demand conscious intervention to even a small percentage of the input that assaults the sensory receptors. How could one be expected to simultaneously address input from touch, taste, sight, smell, hearing, kinesthetic awareness, proprioception, balance mechanisms and more, while sorting and responding to each?  Well, maybe just do this automatically, without a thought.

The fact that so many decisions and responses are regulated unconsciously by the autonomic nervous system is a blessing when the nervous system is normal and healthy.  However, it can seem like a curse when bizarre symptoms arise from an overly excited, sensitized system being influenced by a multitude of factors that seem unrelated.

To compound this, sensitization of the central and peripheral nervous systems is often present yet overlooked in medical practice and omitted from most general health exams. 

An Easy Target

Tissue damage is an easy target for blame in the area of chronic pain and is usually the first cause that most therapists consider. Although tissue damage may be directly or indirectly involved, it is only one of the many factors that lead to complex, individual patterns of presentation and behavior. Alongside this may be confusing symptoms associated with conditions of neuropathic origin, such as allodynia, hyper- and hypo-algesia, hyperesthesia, and more.

While it is important to consider neural interferences, ischemia, posture and a host of other musculoskeletal factors that are classically addressed by massage therapists, it is also critical to not overlook perpetuating factors that influence the nervous system in less obvious ways.

Neuroexcitants and neurostimulants that are harmless in normal amounts in normal tissues may become neurotoxic in abnormal amounts or in sensitized tissues. As the name implies, a neurotoxin, which can act on a local or at a systemic level, can adversely affect the function of the nervous system or damage its components.

Many neurotoxins are found in nature, such as the venom of bees, scorpions, spiders, snakes and some sea life.  Many of these cause swelling, extreme pain, and a rapid onset of paralysis due to depolarization of or damage to nerve and muscle fibers. Other exogenous neurotoxins include liquids (ethanol), gases (carbon monoxide), metals (mercury, lead, arsenic) or a variety of solids.

The immediate effects of neurotoxins are largely dependent on dosage, as seen by the mild neurotoxic effect of inebriation with low dosage ethanol (alcohol) contrasted with the possibility of death from a very large dose. Of course, serious health consequences can also be associated with consistent exposure over time.

Mercury is one of the most harmful neurotoxins on earth. It is present in certain light bulbs, older thermometers, in some batteries, and as an environmental contaminate through industrial projects. Personal exposure is most often from three sources: fish consumption (especially shark, swordfish, king mackerel and tilefish), dental amalgams (especially when being removed) and certain vaccines (i.e., those containing thimerosal).

Tissue Damage

At normal levels, excitatory neurotransmitters, such as acetylcholine, epinephrine, serotonin, and glutamate, increase the chance of neural transmission. Excessive secretion or a sudden internal spillage (stroke, head injury) can become neurotoxic and can result in tissue damage. For instance, glutamate (glutamic acid) is a primary neurotransmitter in the brain and the most abundant neurotransmitter in the nervous system.

In appropriate amounts within food, such as slow-roasted protein, glutamic acid is responsible for “umami,” now referred to as the fifth sense of taste that accompanies sweet, sour, salty and bitter.

However, in excess or with prolonged exposure, it may become excitotoxic, leading to neuronal damage and, literally, exciting the cell to an apoptotic-like death. Certain neurodegenerative diseases, such as multiple sclerosis, Parkinson’s disease, Huntington’s disease, stroke and traumatic brain injury, have been associated with overstimulation of glutamate receptors.

Monosodium glutamate (MSG), a common flavor enhancer, has long been blamed by consumers as the cause of a long list of symptoms and has been the focus of research for decades. With conflicting reports at hand, the FDA requested that the Federation of American Societies for Experimental Biology (FASEB) review the scientific data. They concluded that an unknown percentage of the population may react to MSG with a variety of symptoms that include burning, numbness, tingling, pressure or tightness in various areas of the body, headache, nausea, rapid heartbeat, difficulty breathing, drowsiness, weakness and an array of other symptoms.

Reactions to MSG can be influenced by a number of factors, including the amount of MSG consumed, how empty the stomach is when consumed, if the food is in liquid form, and pre-existing conditions, such as vitamin B6 deficiencies or poorly controlled asthma. Although research does not point to MSG as a public health hazard, it is clear from the report that it can certainly be problematic to certain individuals.

Similar to the MSG controversy, there are concerns regarding the safety of a well-known artificial sweetener, aspartame (aka, Nutrasweet). Aspartame is metabolized and absorbed very quickly; it breaks down into phenylalanine (reduces levels of dopamine and serotonin), methanol (associated with CNS depression, vision disorders), and aspartic acid.

Aspartame can spike blood plasma levels of aspartic acid (aspartate), resulting in hyper-excitability of neurons. Although the degree to which aspartame affects the general population remains unclear, the impact on people born with a genetic inability to metabolize phenylalanine, diagnosed as phenylketonuria, is indisputable and can result in a curious collection of symptoms.

Long-Term Effects

Medical procedures, chemo and other drug therapies, radiation treatment, exposure to pesticides, industrial or cleaning solvents, cosmetics and food sensitivities can all have neurotoxic consequences. Although symptoms may appear immediately after exposure (as when exposed to paint fumes or glue), in many cases long-term effects do not onset for days, weeks or even years.

Symptoms cover a wide range, including headache, behavioral and cognitive problems, sensory and motor challenges, loss of vision, memory issues, and sexual dysfunction.

Caffeine, such as in tea, coffee, cola and chocolate, is consumed by a majority of the adult population. Unlike smoking or alcohol, when consumed in moderate amounts, caffeine does not appear to produce any major health hazards to the consumer nor directly pollute the environment of others.

Caffeine’s use in cancer research and cell life is promising and its universal use as a stimulant for the sleep deprived is well appreciated. More health problems potentially stem from what is added to the product—cream, sugar, artificial sweeteners; what it is served in—aluminum can, Styrofoam cup; and perhaps simply from a skewed perception of what in moderation means.

Myofascial Masqueraders

Many symptoms that present as neuronal and myofascial pain are masqueraders from other tissues. These can originate in viscera, such as when kidney stones cause quadratus lumborum spasms or when the heart refers tingling, numbness or weakness in the left arm and hand; joint surfaces, such as the hip joint refers to groin or thigh; muscle-to-muscle, as with referral from trigger points; and from many sources in disturbed biochemistry.

What does all of these mean for the massage therapist? When the practitioner is applying high quality hands-on treatment and the client is making changes in habits of use, yet the problem persists, it is important not to delay consideration of these and other factors as the possible root cause of the pain presentation.

Know how to recognize medical emergencies and do not hesitate to send the person to an appropriate practitioner when symptoms warrant. Delaying professional referral for a medical evaluation can have serious consequences, particularly when the source is visceral pathology or neural compression.

Continuing to gain only temporary relief on a weekly basis can allow an undiagnosed cancer to grow or lead to permanent neural damage when appropriate treatment is delayed. Sometimes the best course of treatment is professional referral.

Judith DeLany

About the Author:

Judith DeLany is owner and director of NMT Center, which focuses on neuromuscular therapy training, American version, in seminar and massage school programs.


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