Case History: In Search of a Chemical Etiology

by William M. Simpson, Jr., M.D.

Last month a middle-aged client was referred to the Agromedicine Program for consultation regarding his gradually developing "stocking-glove" distribution of decreased sensation in all four extremities. He also reported that he was experiencing a very mild decrease in grip strength.

After being evaluated by a neurologist, the patient sought further consultation in search for a chemical cause of his illness. Since he had applied various pesticides as a youth on his family's farm and has operated a carpet cleaning business for the past 20 years, he was concerned that prior or current exposure to chemicals was responsible. The patient was asked to produce a list of chemicals regularly used in his carpet cleaning business. Most were detergents and there were several hydrocarbons. Peripheral nervous system symptoms, as he described them, have not been reported to be associated with any of these chemicals.

The differential diagnosis for a patient of this type is extremely broad. Nontoxicological causes predominate (diabetes, thyroid disease, uremia, vasculitidies and other connective tissue diseases; among many others). Toxins may also be involved, most commonly ethanol, isoniazid, and vincistine. Arsenic, lead and other heavy metals may also contribute. The patient thought he had applied arsenicals to orchards years ago, but he was not sure of this.

While arsenic is rarely used on edible crops or orchards today, it is still used as a herbicide in turf grass production and maintenance. If arsenic is present in the inorganic form at levels >25micrograms/24hours in urine, the possibility of intentional poisoning must be considered. 1

The patient was advised to work with his neurologist and primary care physician to rule out non-toxicological causes of his illness before focusing on a chemical cause. Should disease be ruled out, then it would be appropriate to investigate possible occupational and non-occupational exposures to heavy metals in his environment.

1Dart RC, ed .The 5 minute toxicology consult., Lippincott Williams & Wilkins, Philadelphia, 2000, p. 236-7.

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