A commonly overlooked cause of extremity pain results from injury to small nerves subsequent to solvent exposure. Commonly encountered chemicals can cause pathology to develop over the course of months to years. The nature of these problems is such that determination of the source of pathology takes time and patience. As it is with most problems, correction cannot be attained without precise diagnosis.
Peripheral neuropathies can result from exposure to common household and shop chemicals. Gasoline, industrial solvents, cleaning supplies, hobby supplies as well as agricultural chemicals such as pesticides, herbicides, acaricides, and fungicides easily penetrate the skin and enter the body.
The ubiquitous nature of ‘warning labels’ has jaded the public to the real danger imposed by environmental threats, and because these chemicals are freely available to anyone willing to buy them, the individual may be drawn into a false sense of security as it relates to the safety of these agents. Unfortunately, as many of these commonly used compounds are allowed to contact the skin, these chemicals cause tremendous damage.
The skin is the largest organ system in the human body, and it affords remarkably little protection from the environment. Due to the physical and chemical nature of the skin, many chemical compounds quickly penetrate the skin and enter the blood steam. Molecular weight and polarity influence the rate and nature of absorbance. Molecular shape and solubility are important factors in understanding skin transport. The skin does provide some protection, but the protection varies depending upon the location on the body. The blood itself affords some protection from many of these chemicals through the presence of a number of available enzymes, and often, this protection is entirely satisfactory. Unfortunately, these enzyme systems can be compromised by commonly used medications, and these enzymes do not protect from many of the hydrocarbons and petroleum distillates. The human metabolism affords little, if any protection from heavy metals, which are often found in some fuel oils, lubricants and herbicides.
In addition to the transdermal route of chemical entry, the lungs can provide an easy route for these common poisons to enter the body. If solvents and pesticides are used in poorly ventilated areas, or if spray application results in the inhalation of the aerosols, the lungs provide little, if any, protection, and the chemical agents pass extremely quickly into the lungs, and then, directly to the peripheral tissues, viscera and brain. Gasoline and kerosene are commonly used to clean grease from the hands. Solvents such as carburetor cleaner and paint thinner are often splashed about with little appreciation or understanding for the damage that is being done.
The effect of the chemicals can be immediate, as in the case of nerve gasses, or it can occur slowly, insidiously, over time. The nervous system is probably the most sensitive organ system in the body, as it pertains to solvent and pesticide toxicity. Over time, exposure to these chemicals results in measurable quantities in the blood stream, and certain organs and tissues can be slowly and irreversibly damaged.
Situations where an exposure is large or overwhelming, kidney or liver failure can result. More commonly, however, small exposures over a long period of time results in the situation where the resulting damage is most noticeable in the nerve fibers going to the hands, feet, eyes ears and heart.
Burning of the hands and feet, similar to that of diabetes may be the first symptom. Tingling sensations, weakness, difficulty maintaining balance, and memory problems may occur.
Treatment of chemical neuropathy involves the manipulation of several metabolic systems. An understanding of the physical nature of this problem is essential to the development of an effective course of treatment.
The site of pathology in most patients with chemical neuropathy involves the myelin surrounding the axonal structure. Damage to the Schwann Cell results in segmental demyelination, retardation of conduction velocity, and deafferentation. Therapy must be directed at the Schwann Cell first, while eliminating any continuing exposure to the chemical agent.
Thoughtful intervention improves the likelihood of recovery. Reversal of the damage can be expected with improvement over time. Topical application of progesterone promotes remyelination, and therapeutic use of essential fatty acids, alpha lipoic acid and DHEA provide the foundation of therapy.
Symptomatic relief is often achievable with intelligent use of anti-convulsing medication. Low dosages are often effective if selection results in GABA-a and GABA-b receptor coverage. Potentiation of effect is achieved with minimal dosages of long acting benzodiazepines, such as clonazepam or lorazepam. Additionally, some patients achieve incremental relief with the concurrent use of oral B-complex vitamins and sublingual B-12. Topical gabapentin can provide remarkable symptomatic relief within a matter of a few minutes. Pain relief is quite often achieved without the need of opiates.
While the only real cure for this serious problem is careful avoidance of skin contact to petroleum based solvents, the diagnosis of ‘peripheral neuropathy’ need not result in life-long pain.