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March 23, 2004 Vol. 53, No. 6 AN EPIDEMIOLOGY PUBLICATION OF THE OREGON DEPARTMENT OF HUMAN SERVICES Telephone 503/731-4024 Emergencies 503/731-4030 Fax 503/731-4798 PESTICIDE POISONING FROM SYNTHETIC PYRETHROIDS WHEN HEALTH CARE providers think about pesticides, organophosphates (OPs) and their cholinergic symptoms come to mind. Welcome to a new generation of insecticides —pyrethroids. Pyrethroids are a synthetic derivative of pyrethrins, a natural insecticide produced from chrysanthemums. Pyrethroids act as contact poisons, affecting the insect’s nervous system. However, they are not cholinesterase inhibitors like OPs; they are, rather, dermal and respiratory allergens. Contact dermatitis, rhinitis and asthma have occurred following exposure. Pyrethroids are replacing OPs in insecticides in bugbombs, head lice treatments, and flea sprays for pets, and are commonly used in fruit orchards. Brand names include Nix®, Elimite®, Dragon®, Drione®, Pyrenon® and Pyrocide®. Suspected pesticide-related illness and injury have been reportable in Oregon since 1987 (OAR 333-017-0000 through 333-019-0046). For incidents reported to the Pesticide Poisoning Prevention Program in the years 2000–2002, the active pesticide ingredients associated with the largest number of likely pesticide illness were pyrethrins and their synthetic versions, pyrethroids. Pesticide poisoning in general can be difficult to diagnose, and poisoning by pyrethroids is no exception. Symptoms may include headache, fatigue, peripheral neuropathy, and vomiting. A thorough history is generally necessary to identify pesticides as the cause. SYNTHETIC PYRETHROIDS AND PARESTHESIAS Scenario: A 58-year old adult male with a history of well-controlled insulindependent diabetes mellitus visits his physician, complaining of tingling and numbness on the fingers and dorsum of the hands. The symptoms began 12 hours before the office visit. The patient reports that the symptoms worsen when he washes his hands with warm water. He has no other symptoms. He has had similar episodes of tingling and numbness of the hands on 3 occasions in the past several months. On each occasion, the tingling and numbness occurred in different areas of the hands. In each case, the symptoms resolved after 12–24 hours. On examination, the patient appears healthy. Inspection of the hands does not reveal rash, erythema, or edema. The hands are warm, with good peripheral pulses and capillary refill. Neurological examination reveals a slight decrease in sensation to light touch in the index finger of the right hand and on the dorsum of the thumb and index finger of the left hand. When testing for temperature sensation, the patient reports an exacerbation of symptoms after a warm stimulus. Neurological examination of the lower extremities and the remainder of the physical examination are unremarkable. Blood work reveals a hemoglobin A1c of 6.3% (indicating good control of blood sugar). A dipstick urinalysis is positive for trace levels of protein. The doc is concerned about peripheral neuropathy, and schedules the patient for nerveconduction studies and a follow-up appointment to reassess his current diabetes treatment regimen. The patient cancels the follow-up appointment after his symptoms resolve within 24 hours of the office visit. DISCUSSION This case demonstrates the importance of an occupational and environmental exposure history, as the signs and symptoms of acute exposure to certain pesticides can be similar to those of other common medical conditions. This patient was a cabbage farmer whose skin had been exposed to the insecticide on several occasions throughout the growing season. When additional questions were asked about exposures during his farming activities, the patient related several instances of direct skin contact with a concentrated insecticide in which lambda-cyhalothrin was the active ingredient. The exposures occurred when he was mixing and transferring the liquid without the use of appropriate skin protection. An expanded occupational history led to the correct diagnosis and an opportunity to reduce exposure. Lambda-cyhalothrin is an insecticide registered for use in the US by the Environmental Protection Agency. It is a synthetic pyrethroid. Synthetic pyrethroids affect the nervous system of insects by prolonging the deactivation of voltage-gated sodium channels, which results in prolonged excitation of nerve fibers.1 There is evidence that synthetic pyrethroids, which, like lambda- cyhalothrin, contain an alpha-cyano group are more potent in eliciting neurotoxic effects, compared to pyrethroids that lack this group, e.g., permethrin1,2 (see figures). Chemical structure of lambda-cyhalothrin (nasty alpha-cyano group below bracket) Year Total Cases Associated with Cases Pyrethrins/Pyrethroids 2000 200 35 2001 213 35 2002 194 31 Reported Pesticide-Related Illness Associated with Pyrethrins/Pyrethroids, Oregon Chemical structure of permethrin


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