Organophosphate poisoning

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Overview

Many organophosphates are potent neurotoxins, functioning by inhibiting the action of acetylcholinesterase (AChE) in nerve cells. They are one of the most common causes of poisoning worldwide, and are frequently intentionally used in suicides in agricultural areas.

Effects

The effects of organophosphate poisoning are recalled using the mnemonic SLUDGE (Salivation, Lacrimation, Urination, Diaphoresis (or Defecation), Gastrointestinal motility, Emesis)

Treatment

Atropine can be used as an antidote in conjunction with pralidoxime, though the use of "-oximes" has been found to be of no benefit, or possibly harmful, in at least two meta-analyses.

Potential effects of environmental organophosphates

The use of the organophosphates in aviation lubricating oils and hydraulic fluids and its impact on health and flight safety is a matter of some debate. Airline employees set up a non profit group in 2001 to highlight their concerns called the Aviation Organophosphate Information Site (AOPIS).

Purdey (1998) suggested that organophosphates, in particular Phosmet, induced the transmissible spongiform encephalopathy epidemic of BSE. An European Union food safety Scientific Steering Committee examined the evidence and did not find a link.

As opposed to the two examples given above, the toxicological literature on persistent chronic toxicity from acute poisonings or long-term low level exposure is quite extensive. The phenomenon of OPIDP (organophosphate induced delayed polyneuropathy, also OPIDN), which causes degeneration of the peripheral nerves, has been noted to occur several weeks after exposure to some organophosphates.

Ginger Jake

A striking example of OPIDN occurred during the 1930s Prohibition Era when thousands of men in the American South and Midwest developed arm and leg weakness and pain after drinking a "medicinal" alcohol substitute. The drink, called "Ginger Jake," contained an adulterated Jamaican ginger extract containing tri-ortho-cresyl phosphate (TOCP) which resulted in partially reversible neurologic damage. The damage resulted in the limping "Jake Leg" or "Jake Walk" which were terms frequently used in the blues music of the period. Europe and Morocco both experienced outbreaks of TOCP poisoning from contaminated abortifacients and cooking oil, respectively.

Effects

Other studies suggest a link between chronic low level organophosphate exposure and neuropsychiatric and behavioral effects. Jamal has suggested the term COPIND, or "Chronic Organophosphate-Induced Neurologic Dysfunction," and Abou Donia the term, OPICN, or Organophosphate-Induced Chronic Neuropathy for describing these effects.

Low-level effects on the developing brains of fetuses, infants, and children have been documented as well.

Differential Diagnosis

Organophosphate poisoning should be differentiated from other causes of muscle weakness, hypotonia and flaccid paralysis. The differentials include the following:

Diseases	History and Physical								Diagnostic tests		Other Findings
	Motor Deficit	Sensory deficit	Cranial nerve Involvement	Autonomic dysfunction	Proximal/Distal/Generalized	Ascending/Descending/Systemic	Unilateral (UL) or Bilateral (BL) or No Lateralization (NL)	Onset	Lab or Imaging Findings	Specific test
Acute Flaccid Myelitis	+	+	+	-	Proximal > Distal	Ascending	UL/BL	Sudden	MRI (Longitudinal hyperintense lesions)	MRI and CSF PCR for viral etiology	Drooping eyelids Difficulty swallowing Respiratory failure
Adult Botulism	+	-	+	+	Generalized	Descending	BL	Sudden	Toxin test	Blood, Wound, or Stool culture	Diplopia, Hyporeflexia, Hypotonia, possible respiratory paralysis
Infant Botulism	+	-	+	+	Generalized	Descending	BL	Sudden	Toxin test	Blood, Wound, or Stool culture	Flaccid paralysis (Floppy baby syndrome), possible respiratory paralysis
Guillian-Barre syndrome	+	-	-	-	Generalized	Ascending	BL	Insidious	CSF: ↑Protein ↓Cells	Clinical & Lumbar Puncture	Progressive ascending paralysis following infection, possible respiratory paralysis
Eaton Lambert syndrome	+	-	+	+	Generalized	Systemic	BL	Intermittent	EMG, repetitive nerve stimulation test (RNS)	Voltage gated calcium channel (VGCC) antibody	Diplopia, ptosis, improves with movement (as the day progresses)
Myasthenia gravis	+	-	+	+	Generalized	Systemic	BL	Intermittent	EMG, Edrophonium test	Ach receptor antibody	Diplopia, ptosis, worsening with movement (as the day progresses)
Electrolyte disturbance	+	+	-	-	Generalized	Systemic	BL	Insidious	Electrolyte panel	↓Ca++, ↓Mg++, ↓K+	Possible arrhythmia
Organophosphate toxicity	+	+	-	+	Generalized	Ascending	BL	Sudden	Clinical diagnosis: physical exam & history	Clinical suspicion confirmed with RBC AchE activity	History of exposure to insecticide or living in farming environment. with : Diarrhea, Urination, Miosis, Bradycardia, Lacrimation, Emesis, Salivation, Sweating
Tick paralysis (Dermacentor tick)	+	-	-	-	Generalized	Ascending	BL	Insidious	Clinical diagnosis: physical exam & history	-	History of outdoor activity in Northeastern United States. The tick is often still latched to the patient at presentation (often in head and neck area)
Tetrodotoxin poisoning	+	-	+	+	Generalized	Systemic	BL	Sudden	Clinical diagnosis: physical exam & dietary history	-	History of consumption of puffer fish species.
Stroke	+/-	+/-	+/-	+/-	Generalized	Systemic	UL	Sudden	MRI +ve for ischemia or hemorrhage	MRI	Sudden unilateral motor and sensory deficit in a patient with a history of atherosclerotic risk factors (diabetes, hypertension, smoking) or atrial fibrillation.
Poliomyelitis	+	+	+	+/-	Proximal > Distal	Systemic	BL or UL	Sudden		PCR of CSF	Asymmetric paralysis following a flu-like syndrome.
Transverse myelitis	+	+	+	+	Proximal > Distal	Systemic	BL or UL	Sudden	MRI & Lumbar puncture	MRI	History of chronic viral or autoimmune disease (e.g. HIV)
Neurosyphilis	+	+	-	+/-	Generalized	Systemic	BL	Insidious	MRI & Lumbar puncture	CSF VDRL-specifc CSF FTA-Ab -sensitive	History of unprotected sex or multiple sexual partners. History of genital ulcer (chancre), diffuse maculopapular rash.
Muscular dystrophy	+	-	-	-	Proximal > Distal	Systemic	BL	Insidious	Genetic testing	Muscle biopsy	Progressive proximal lower limb weakness with calf pseudohypertrophy in early childhood. Gower sign positive.
Multiple sclerosis exacerbation	+	+	+	+	Generalized	Systemic	NL	Sudden	↑CSF IgG levels (monoclonal)	Clinical assessment and MRI	Blurry vision, urinary incontinence, fatigue
Amyotrophic lateral sclerosis	+	-	-	-	Generalized	Systemic	BL	Insidious	Normal LP (to rule out DDx)	MRI & LP	Patient initially presents with upper motor neuron deficit (spasticity) followed by lower motor neuron deficit (flaccidity).
Inflammatory myopathy	+	-	-	-	Proximal > Distal	Systemic	UL or BL	Insidious	Elevated CK & Aldolase	Muscle biopsy	Progressive proximal muscle weakness in 3rd to 5th decade of life. With or without skin manifestations.

Review

The U.S. Food Quality Protection Act (FQPA), passed in 1996, designated the United States Environmental Protection Agency (EPA) to conduct a 10 year review process of the health and environmental effects of all pesticides, beginning with the Organophosphates. The process has taken longer than expected, but was recently concluded and eliminated or modified thousands of uses. NYTimes Aug 4, 2006

Many non-governmental and research groups, as well as the EPA's Office of Inspector General, have published concerns that the review did not take into account possible neurotoxic effects on developing fetuses and children, an area of developing research. OIG report. A group of leading EPA scientists sent a letter to the chief administrator, Stephen Johnson, decrying the lack of developmental neurotoxicity data in the review process. EPA Letter EHP article New studies have shown toxicity to developing organisms during certain "critical periods" at doses much lower than those previously suspected to cause harm.

See also

• Nerve agent