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Hemlock water dropwort (Oenanthe crocata) is perhaps the most poisonous indigenous plant in Britain.1 It is a member of the Umbellifer family and is found in ditches, damp meadows, in steams, by riverbanks, and in marshes. It is a large, stout plant between three and five feet high that flowers in July. The lower stem is usually thick and joins to clusters of fleshy tubers that gives rise to the popular name “dead man’s fingers”.
The entire plant is poisonous. The tubers, stems, and leaves contain oenanthotoxin, a highly unsaturated higher alcohol, which is known to be poisonous and a powerful convulsant.2
The majority of the umbellifer family are harmless. These include species of celery, parsley, parsnip, and carrots. The poisonous members are hemlock (Conium maculatum), cowbane (Cicuta virosa), and hemlock water dropwort.3
Poisoning by hemlock water droplet is an infrequent event. A number of human fatalities have occurred over the years, although animals are its usual victims.
A group of eight young adults who were on holiday in Argyll collected what they thought were water parsnips from a small stream. The roots were cleaned, chopped, and added to a curry. All consumed the curry, but the majority of the group only had a small amount of the root, which was easily identifiable in the curry, partly because there was some doubt regarding its nature and partly because of its bitter taste.
Early the next morning, 10 hours after ingestion one of the group had a witnessed grand mal seizure lasting about five minutes. He was taken to the community hospital and was in a post-ictal state. No connection at this point was made with the ingestion of the plant root the night before.
Gradually over the course of the next four hours a number of the group became unwell and nauseated. During this time four of the group consumed the left overs for lunch. One of these individuals, subsequently become increasingly unwell, nauseated, and began to vomit. He had a witnessed grand mal seizures lasting about three minutes. On arrival at the emergency department this person was conscious but vomiting and experiencing visual hallucinations. The patient was agitated, tachycardic, but blood pressure and oxygen saturation were within normal limits. He was hyper-reflexive with dilated pupils, but there were no focal neurological signs. He had one further subsequent grand mal seizure controlled with intravenous diazemuls.
The other patients all had varying degrees of nausea, vomiting, lethargy, sweating, and low grade fever.
Initially it was uncertain from the description as to the identity of the poisonous plant. The community hospital that they were admitted to serves a rural area of Argyll. The police were able to take an asymptomatic member of the group to the stream to recover a further plant. The police knew of a local botanist in the area who was able to positively identify the specimen (fig l).
Four of the group required admission to the hospital. The person who had required intravenous diazemules, was observed over the next 48 hours. Biochemical and haematological parameters were all within normal limits, and his symptoms settled rapidly. The other three were discharged after 24 hours.
Hemlock water dropwort poisoning is rare in humans and the number of people in this case report is very unusual. The main toxic constituent of hemlock water dropwort is oenanthotoxin. The concentration of this poison in the plant roots is highest in winter and spring and ingestion of very small amounts may prove fatal.2 These events occurred in April when the concentration of toxin is still high. Oenanthotoxin is, however unstable,4 and the boiling involved in making the curry resulted in an amelioration of the toxic effects, both in the severity of symptoms, and in the time delay until presentation.
Accidental ingestion of water hemlock most commonly occurs by mistaken identification, particularly differentiation from water parsnip as in this case. The majority of cases reported have involved children and young adults.4–8 The mortality rate is quantity dependent, but has been reported as between 30%–70%.2,8
The clinical features that have been previously reported include nausea, increased salivation, and vomiting. There may be tremor, abdominal cramps, and diarrhoea. Grand mal seizures and opisthotonus can rapidly develop, which may be attributable to antagonism of an inhibitory transmitter in the brain stem. Blood pressure falls, pupils normally dilate, and electrolyte imbalances occur. The latter includes high sodium and potassium and creatinine, a lymphocytosis and very low sodium bicarbonate levels. Increased muscular activity and damage results in a metabolic acidosis.6,8 Acute renal failure secondary to rhabdomyolysis has been reported.8,9
Treatment is symptomatic. If vomiting has not occurred before seeking medical advice, which is unlikely, then the stomach should be emptied. Control of seizures is best performed using intravenous diazemules.10,11 Phenytoin would be the second line drug of choice. Thiopentone sodium has been recommended for seizure control because of its faster action. Treatment for resistant seizures may necessitate intubation and ventilation.
This episode highlighted some difficulties that can relate to plant poisoning. In this case the cause of the poisoning was not readily apparent, but with the assistance of the local police we were able to locate a plant specimen, and use a local botanist to aid identification. This facilitated an appropriate management strategy, although in this case the treatment was supportive. As a result of this the hospital has now invested in specific resources that relate to plant poisoning, and people in the community who have expertise in plant identification have been identified, and have agreed to be contacted in the event of suspected poisoning. A copy of this list has been distributed to local general practitioners and the police.
It is possible that with increasing interest in “natural” foods accidental poisoning of this nature may become more frequent. These cases illustrate the potential dangers of this, but highlight the fact that even in small communities expertise is available and if accessed appropriately can be invaluable.