Introduction
Background
Plant ingestions continue to be a very common exposure for humans (particularly children) and animals, and they account for nearly 100,000 calls to national poison centers annually. Pediatric patients comprise more than 80% of plant-related exposures. Only a few plants, poison hemlock and water hemlock included, are associated with potentially life-threatening toxicity, and less than 20% of plant exposures require medical management.
Hemlock poisoning may refer to poisoning by either poison hemlock (Conium maculatum) or water hemlock (Cicuta maculata). Historically, poison hemlock was reportedly used to execute Socrates and the Old Testament describes rhabdomyolysis in Israelites who consumed quail fed on hemlock.
Although related, poison hemlock and water hemlock toxicity have different pathophysiologies and clinical presentations. The root contains the greatest concentration of toxin in both species, although all plant parts are toxic. Poison hemlock causes "crooked calf disease," a congenital abnormality, among cattle formed via fetal exposure. No antidote is available for either toxin.
Poison hemlock, an exotic species introduced to the US, is a ubiquitous plant with fernlike properties that may reach a height of 2 meters. Poison hemlock grows in diverse settings, including wooded areas, ditches, and waysides throughout the US, and may be mistaken for other plants such as fool's parsley (Aethusa cynapium).
Hemlock. Photo by Cornell University Poisonous Plants Informational Database
Water hemlock is typically found growing in moist habitats, such as drainage ditches, marshes, and near bodies of fresh water. Water hemlock has compound leaves, small white or green flowers, and tuberous, large, hollow roots. Water hemlock may reach a height of 2.5 meters and can also be confused with other plants such as wild carrot, also known as Queen Anne's lace (Daucus carota), or poison hemlock (C maculata).
Pathophysiology
Poison hemlock contains several piperidine alkaloid toxins (namely coniine) that are structurally similar to nicotine. Coniine has direct effects on nicotinic (cholinergic) receptors, both agonist and antagonist. Clinically, initial manifestations include gastritis and CNS stimulation (tremor, ataxia, and seizures). Nicotine activation at autonomic ganglia can cause tachycardia, salivation, mydriasis, and diaphoresis. In severe cases, acetylcholine (nicotinic) receptor antagonism develops. This leads to bradycardia, ascending paralysis, and CNS depression (coma). Death is typically from respiratory failure.
Water hemlock contains cicutoxin, a potent, noncompetitive gamma-aminobutyric acid (GABA) receptor antagonist. Using a rat model, Uwai et al showed that cicutoxin is an antagonist of GABA-mediated chloride channels.1 Cicutoxin rapidly produces GI symptoms (nausea, emesis, abdominal pain) typically within 60 minutes of ingestion. CNS excitation leads to tremor and seizures, often refractory to therapy. A single bite of the root, which contains the highest concentration of cicutoxin, has been reported to kill an adult.
Frequency
United States
In 2003, 77,169 plant exposures were reported to the American Association of Poison Control Centers Toxic Exposure Surveillance System.2 No human deaths from hemlock ingestion were reported to US Poison Control Centers from 1997-2003. Prevalence was low for US livestock.
International
Livestock exposures in New Zealand, South America, Europe, and southern Canada have been reported. Cattle appear to be most vulnerable to hemlock toxicity.
Mortality/Morbidity
Poison hemlock poisoning is potentially lethal with large ingestions; water hemlock fatalities have occurred following a few bites of the root.
- Poison hemlock's human median lethal dose (LD50) is not known. Mortality from poison hemlock ingestion is usually secondary to respiratory paralysis.
- Water hemlock had a 30% mortality rate in one series of 86 patients. Mortality from water hemlock is usually secondary to refractory status epilepticus.
Age
Younger patients are theoretically at increased risk due to smaller body mass.
Clinical
History
In cases of plant toxicity, history may be obscure and ingested plants may not be available for identification.
- Poison hemlock
- Nausea and vomiting
- Abdominal pain
- Tachycardia
- Tremor
- Seizures (much more common with water hemlock)
- Bradycardia (late)
- Ascending paralysis (late)
- Coma
- Respiratory failure
- Water hemlock
- Nausea and vomiting
- Abdominal pain
- Delirium
- Convulsions, opisthotonus, hemiballismus
- Seizure (status epilepticus)
Physical
- Poison hemlock: Signs of poison hemlock toxicity can be divided into an early stimulation phase and, in severe poisonings, a later depressant phase.
- Emesis
- Salivation
- Mydriasis
- Tachycardia, then bradycardia
- Initial fasciculations, then flaccid paralysis
- Hypoventilation, respiratory arrest
- Water hemlock: Signs of water hemlock toxicity begin with GI symptoms, which are rapidly followed by CNS excitation.
- Emesis
- Mydriasis
- Agitation
- Delirium
- Convulsions
- Seizures
- Coma
Causes
- Hemlock plants may be intentionally ingested. However, most ingestions are accidental.
- Poison hemlock may be mistaken for wild carrots.
- Water hemlock may be mistaken for wild parsnips or artichokes.
- Birds ingesting hemlock during migratory flight may be reported to cause coturnism (human poisoning after eating quail).
More on Plant Poisoning, Hemlock |
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| Follow-up: Plant Poisoning, Hemlock |
| Multimedia: Plant Poisoning, Hemlock |
| References |
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References
Uwai K, Ohashi K, Takaya Y. Exploring the structural basis of neurotoxicity in C(17)-polyacetylenes isolated from water hemlock. J Med Chem. Nov 16 2000;43(23):4508-15. [Medline].
Watson WA, Litovitz TL, Klein-Schwartz W, et al. 2003 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. Sep 2004;22(5):335-404. [Medline].
Ellenhorn MJ. Poison hemlock (Conium Maculatum). In: Ellenhorn's Medical Toxicology. 2nd ed. Williams and Wilkins; 1997:1841, 1871.
Furbee B, Wermuth M. Life-threatening plant poisoning. Crit Care Clin. Oct 1997;13(4):849-88. [Medline].
Goldfrank LR, Flomenbaum NE, Lewin NA, et al, eds. Goldfrank's Toxicologic Emergencies. 6th ed. Appleton & Lange; 1998:2, 318, 338, 1246, 1252-3.
Hopkins J. The glycoalkaloids: naturally of interest (but a hot potato?). Food Chem Toxicol. Apr 1995;33(4):323-8. [Medline].
Krenzelok EP, Jacobsen TD. Plant exposures ... a national profile of the most common plant genera. Vet Hum Toxicol. Aug 1997;39(4):248-9. [Medline].
Litovitz TL, Klein-Schwartz W, Caravati EM. 1998 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. Sep 1999;17(5):435-87. [Medline].
Litovitz TL, Klein-Schwartz W, Dyer KS. 1997 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. Sep 1998;16(5):443-97. [Medline].
Litovitz TL, Klein-Schwartz W, White S. 1999 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. Sep 2000;18(5):517-74. [Medline].
Lopez TA, Cid MS, Bianchini ML. Biochemistry of hemlock (Conium maculatum L.) alkaloids and their acute and chronic toxicity in livestock. A review. Toxicon. Jun 1999;37(6):841-65. [Medline].
Olson KR. Hemlock. In: Poisoning and Drug Overdose. 3rd ed. Appleton & Lange; 1999:22, 25, 30, 265-74.
Panter KE, James LF, Gardner DR. Lupines, poison-hemlock and Nicotiana spp: toxicity and teratogenicity in livestock. J Nat Toxins. Feb 1999;8(1):117-34. [Medline].
Reynolds T. Hemlock alkaloids from Socrates to poison aloes. Phytochemistry. 2005;66(12):1399-1406. [Medline].
Vetter J. Poison hemlock (Conium maculatum L.). Food Chem Toxicol. Sep 2004;42(9):1373-82. [Medline].
Watson WA, Litovitz TL, Rodgers GC, et al. 2002 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. Sep 2003;21(5):353-421. [Medline].
Further Reading
Keywords
hemlock, plant poison hemlock, poison hemlock, Conium maculatum, C maculatum, water hemlock, Cicuta maculata, C maculata, plant ingestion, Queen Anne's lace, wild carrot, fool's parsley
