There are environmental conditions and contaminates that can cause common neurological symptoms of numbness, tingling, paresthesia, pain, and weakness. Would you recognize the symptoms of neurotoxicity? Only the astute doctor of chiropractic is going to evaluate the possibility of lead toxicity, arsenic poisoning, solvent or pesticide exposure. Increasing use of chemicals in our workplaces and home environments suggests that all clinicians should be aware of potential overlap into their specialty. Being aware of other causes of neurologic abnormality could save someone's life by referring them for proper care.
There are presently five to six million chemicals of known molecular structure. Scientists are synthesizing new chemicals at a rate of approximately 6,000 per week. Scientists have identified over 600 rodent carcinogens and 2000 teratogens. Toxicity testing has been accomplished on only about 1% of the thousands of chemicals in agricultural and industrial settings (Brooks, Benson, & Grochfeld, 1995). Linz and Garling report that a compendium of neurotoxic compounds is over 750 chemicals long. Common neurotoxicants may include metals, organic solvents, and pesticides.
Exposure incidents can occur quickly, as in acute contamination from pesticides or solvents. Symptoms may be abrupt in their onset and abate quickly with cessation of exposure and clearing from the body. Subacute and chronic exposures can occur over protracted periods of time, such as lead or arsenic ingestion from contaminated water. With chronic poisoning, a myriad of neurologic symptoms may be present signifying both PNS and CNS toxicity.
When making a neurotoxic diagnosis, consider certain factors such as the dose-response relationship, temporal relationships between exposure and symptoms, immediate injury vs. delayed effect, the identity of the toxicant, and changing signs and symptoms. The dose-response relationship evaluates the exposure dose or quantity and duration of exposure to the toxic compound. A massive exposure is likely to precipitate an immediate toxic response. The patient is able to report knowledge of exposure. Temporal relationships refer to the time between exposure and the onset of symptoms. Acute exposures are most consistent. Prolonged exposure may manifest confusing symptoms that change over time as PNS, CNS, and other systems become damaged by the toxicant. Delayed neuronal death and degeneration may also present unusual temporal relationships. Symptoms may progress despite the abatement of exposure.
There are very few pathognomonic signs and symptoms that illicit the immediate neurotoxic diagnosis. Variations in symptom complex may mimic disorders of psychiatric, metabolic, nutritional, inflammatory, or degenerative natures. Common complaints may include numbness, tingling, pain, weakness, dizziness, and forgetfulness.
Peripheral nervous system toxicity most commonly affects the limbs distally causing symptoms of numbness, tingling, burning pain, or weakness beginning with the fingers and toes first, then the hands, feet, legs, and forearms. Symptoms often follow a classic stocking-glove distribution. There seems to be a greater vulnerability of the longest nerve axons first with sensory dysfunction before motor involvement. Common peripheral nerve toxicants may include metals such as lead, arsenic, and mercury, or solvents like n-hexane, methyl n-butyl ketone, and various organophosphate pesticides and fungicides.
Physical examination features include those common to routine chiropractic evaluation: pinwheel, pinprick, cotton wisp, vibration, deep tendon reflexes, and strength assessment. Deficits are seen peripherally but intact proximal.
Central nervous system toxicity may present a whole host of symptoms from altered cognition and personality features to balance, coordination, motor dysfunction and tremor. For example, manganese toxicity can cause Parkinsonism, while lead, arsenic, and mercury all can cause headaches and other CNS symptoms. Solvents frequently cause CNS depression and thus impair many of the body systems. Pesticides and fungicides cause hyperexcitability of the CNS that leads to suffocation and death.
Clinical evaluation of the CNS should include cognitive assessment, coordination, gait control, vestibular function tests, and cranial nerve assessment. It may be necessary to refer to a neuropsychologist for complex personality and cognitive evaluation in cases of chronic toxicity. Findings may include altered cognitive function, personality changes, ataxia, nystagmus, hearing deficits, and other centrally modulated dysfunctions.
The chiropractic domain of neuromusculoskeletal illness and injury may have a few pitfalls of unfamiliar neurological conditions now and then. Be aware that what seems to be classic neurological symptoms may not have a mechanical causation: investigate those neurological symptoms and ask your patients about exposures to chemicals and substances in their homes or workplaces. Locate an occupational and environmental medicine specialist in your community with whom you may refer to if needed. Good chiropractic is helping the patient, however that may be accomplished.
References
- Amadur MO, Doull J, Klassen CD (eds.) Cassarett and Doull's toxicology, 4th ed. 1991, McGraw Hill Inc., New York.
- Beaulieu HJ, Beaulieu DL. Toxicology. 1991, National Environmental Health Association, Denver.
- Brooks SM, Bensen L, Grochfeld M. Types and sources of environmental hazards. In: Brooks SM, Grochfeld M, Jackson R, Herzstein J, Schenker MB (eds.) Environmental medicine. 1995, Mosby, St. Louis.
- Felder N, Burger J, Grochfeld M. Neurobehavioral toxicity and testing. In: Brooks SM, Grochfeld M, Jackson R, Herzstein J, Schenker MB (eds.) Environmental medicine. 1995, Mosby, St. Louis.
- Linz DH, Garling DJ. Toxicology of selected neurotoxic agents. In: Brooks SM, Grochfeld M, Jackson R, Herzstein J, Schenker MB (eds.) Environmental medicine. 1995, Mosby, St. Louis.
- So YT. Nervous system. In: Brooks SM, Grochfeld M, Jackson R, Herzstein J, Schenker, MB (eds.) Environmental medicine. 1995, Mosby, St. Louis.
- Williams PL, Burson JL. Industrial toxicology. 1995, Van Nostrand Reinhold, New York.
David P Gilkey, DC
Broomfield, Colorado
E-mail:
Dr. David Gilkey is associate professor of ergonomics in the Department of Environmental and Radiological Health Sciences and the distance-education coordinator for ergonomics training at Colorado State University. Dr. Gilkey earned his DC degree from Southern California Health Sciences University and his PhD from CSU with a focus in occupational ergonomics related to low back injury prevention.