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DESCRIPTION
Shellfish food poisoning includes specific syndromes (paralytic, neurotoxic, and amnestic) that develop after the ingestion of shellfish.
FORMS AND USES
- Paralytic shellfish poisoning (PSP) typically begins with a brief gastrointestinal prodrome, followed by sensory disturbances and progressive paralysis.
- Neurotoxic shellfish poisoning features gastrointestinal and neurologic symptoms usually appearing simultaneously; these may include paresthesia of the face, throat, and extremities, burning sensation of the mucous membranes, abdominal pain and cramps, incoordination, seizures, and possibly coma.
- Amnestic shellfish poisoning begins with a gastrointestinal prodrome, followed by confusion, seizures, coma, and long-term memory deficits; hypotension, pulmonary edema, seizures, and coma may develop.
TOXIC DOSE
Paralytic shellfish poisoning (PSP) reportedly can cause illness with as little as 500 µg of the toxin; however, the concentration of toxin in the mollusk varies greatly.
PATHOPHYSIOLOGY
- Dinoflagellates are the major food source for bivalve mollusks such as clams and oysters; toxins produced by certain dinoflagellate species accumulate in the mollusks without injuring the mollusk.
- PSP is caused by saxitoxin and gonyautoxins, toxins that reversibly block sodium channels in nerve and muscle.
- Neurotoxic shellfish poisoning is caused by brevetoxin, a toxin that activates sodium influx into the cell.
- Amnestic shellfish poisoning is caused by domoic acid, an excitatory amino acid.
EPIDEMIOLOGY
- PSP (carried by bivalve mollusks, especially mussels, clams, oysters, scallops, or limpets) occurs on the East and West Coasts of North America, western coast of Europe, and throughout Japan; most outbreaks occur during May to August when the water temperatures are highest.
- Neurotoxic shellfish poisoning (bivalve mollusks) has occurred primarily in Florida and around the Gulf of Mexico.
- Amnestic shellfish poisoning (bivalve mollusks, and occasionally fish and crustaceans) has occurred from eating contaminated mussels from Prince Edward Island, Canada, but domoic acid has also been identified in mollusks harvested from the coastal waters of Washington and Oregon.
CAUSES
Poisoning is usually caused by inadvertent ingestion of contaminated fish.
RISK FACTORS
Children may be more sensitive to shellfish toxins.
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DIFFERENTIAL DIAGNOSIS
- Toxic causes of gastroenteritis followed by neurologic symptoms include scombroid or puffer fish poisoning, botulism, heavy metal toxicity, diphtheria, and nicotine or hemlock poisoning, among others.
- Nontoxic causes include infectious gastroenteritis.
SIGNS AND SYMPTOMS
Vital Signs
- Paralytic. Tachycardia is common.
- Neurotoxic. Bradycardia is common.
- Amnestic. Tachycardia and hemodynamic instability may occur.
HEENT
- Paralytic. The patient may develop nystagmus, temporary blindness, loss of gag reflex, dysphagia, and difficulty speaking.
- Neurotoxic. Mydriasis, conjunctivitis, lacrimation, rhinorrhea, and sneezing may occur.
- Amnestic. The patient may exhibit miosis or mydriasis, disconjugate gaze, and ophthalmoplegia in severe cases.
Cardiovascular
- Paralytic. ECG T-wave changes may develop.
- Neurotoxic. Bradycardia may persist for up to 12 hours.
- Amnestic. Hypotension with peripheral vasodilatation or dysrhythmias may develop.
Pulmonary
- Paralytic. Respiratory failure may develop.
- Neurotoxic. Inhalation of toxin may occur when high winds aerosolize the toxin, resulting in cough, asthma attack, and respiratory irritation in nonasthmatics.
- Amnestic. Excessive pulmonary secretions and pulmonary edema are common.
Gastrointestinal
- Paralytic. Nausea, vomiting, diarrhea, and abdominal pain are common.
- Neurotoxic. Nausea, vomiting, diarrhea, cramping, abdominal pain, and rectal burning pain may occur.
- Amnestic. Nausea, vomiting, diarrhea, and hiccups are common.
Fluids and Electrolytes
All three types of shellfish poisoning may produce dehydration, as well as electrolyte abnormalities in severe cases.
Musculoskeletal
- Paralytic. Incoordination, muscle weakness, and paralysis are common.
- Neurotoxic. Myalgia, weakness, and difficulty walking may develop.
Neurologic
- Paralytic. Paresthesias ("pins and needles") and numbness of lips, tongue, throat, face, neck, and extremities may develop, as may headaches, dizziness, and sensation of lightness.
- Neurotoxic. Paresthesias of the face, lips, and extremities are common; reversal of hot/cold sensation, headache, tremor, decreased reflexes, ataxia, distorted sensorium, vertigo, seizure, and coma may develop.
- Amnestic. Confusion, agitation, seizure, coma, fasciculation, Babinski sign, neuropathy (motor and sensory), and memory loss may occur.
PROCEDURES AND LABORATORY TESTS
Essential Tests
No tests may be needed in minimally symptomatic patients.
Recommended Tests
- For all three types of shellfish poisoning
- Serum electrolytes, BUN, creatinine to assess dehydration from gastroenteritis
- Serum calcium, magnesium, phosphorus to assess other causes of symptoms.
- Serum creatine kinase to assess cardiac and muscle injury
- ECG and cardiac monitoring to monitor for ischemia and dysrhythmia
- For PSP, Electromyogram/nerve conduction velocity should be obtained to assess both motor and sensory abnormality.
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- Treatment should focus on symptomatic and respiratory care, as well as on control of seizure and dysrhythmia.
- Patients should be intubated endotracheally if serious respiratory depression or difficulty in protecting airway develops.
- Dose and time of exposure should be determined for all substances involved.
DIRECTING PATIENT COURSE
The health-care provider should call the poison control center when:
- Shellfish poisoning is suspected.
- Toxic effects are not consistent with shellfish poisoning.
- Drug interaction or underlying disease presents an unusual problem.
The patient should be referred to a health-care facility when:
- The symptoms of shellfish poisoning or other severe effects are present.
- Patient or caregiver seems unreliable.
- Drug interaction or underlying disease presents an unusual problem.
Admission Considerations
Inpatient management in an ICU is warranted for symptomatic patients.
DECONTAMINATION
Out of Hospital
Induced emesis is not recommended.
In Hospital
- Gastric lavage should be considered in pediatric (tube size 24-32 French) or adult (tube size 36-42 French) patients presenting within 1 hour of a large ingestion or if serious effects are present.
- One dose of activated charcoal (1-2 g/kg) should be administered without a cathartic if a substantial ingestion has occurred within the previous few hours.
ANTIDOTES
There is no specific antidote for paralytic, neurotoxic, or amnestic shellfish poisoning.
ADJUNCTIVE TREATMENT
See SECTION II, Patient Presentations with Toxicologic Causes, for more detail on each of the following treatments.
Seizure
- A patent airway must be ensured.
- A benzodiazepine should be administered for initial control.
- If seizures persist or recur, another anticonvulsant such as phenobarbital may be added.
Hypotension
- Hypotension should be treated with isotonic fluid infusion and the Trendelenburg position.
- A vasopressor may be added if needed; dopamine is preferred.
- Norepinephrine may be added for refractory hypotension.
Dysrhythmias or Conduction Abnormalities
- Seizures should be controlled and acidemia corrected.
- If QRS widening or dysrhythmias persist, sodium bicarbonate (1-2 mEq/kg) may be administered in an intravenous bolus; this may be repeated as needed, but arterial pH should not exceed 7.55.
- Lidocaine may be used for ventricular tachycardia or multifocal premature ventricular contractions.
- Adult dose is 1 to 2 mg/kg in an intravenous loading dose, followed by infusion of 2 to 4 mg/min, titrated to desired effect.
- Pediatric dose is 1 mg/kg bolus followed by infusion of 20 to 50 µg/kg/min, titrated to effect.
- The initial dose may be repeated in 10 to 15 minutes at 0.5 to 1.0 mg/kg.
- Bretylium may be added for lidocaine-resistant ventricular dysrhythmia
- Dose is 5 to 10 mg/kg intravenously over 1 minute.
- If this is unsuccessful, additional doses may be administered over 1 minute and repeated as necessary to a total dose of 30 mg/kg.
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PATIENT MONITORING
Cardiac and pulmonary functions should be monitored continuously in symptomatic patients.
EXPECTED COURSE AND PROGNOSIS
Paralytic
- The incubation period is usually less than 30 minutes.
- The duration of illness is hours to days; muscle weakness may last for weeks.
- In severe cases, respiratory muscle paralysis can result in respiratory failure as well as generalized muscle weakness and paralysis.
Neurotoxic
- The incubation period is usually minutes to hours.
- The illness lasts hours to days.
Amnestic
- The incubation period has ranged from 15 minutes to 38 hours.
- Long-term anterograde memory deficits and neuropathy are possible; morbidity appears to be greater in males.
DISCHARGE CRITERIA AND INSTRUCTIONS
- From the emergency department. Asymptomatic patients may be discharged after a 6-hour observation period.
- From the hospital
- PSP patients may be discharged when oral intake is adequate, and respiratory function, musculoskeletal, and neurological signs and symptoms have stabilized.
- Neurotoxic shellfish poisoning patients may be discharged when oral intake is adequate and all signs and symptoms have resolved or are improving.
- Amnestic shellfish patients may be discharged after effects of seizures, pulmonary edema, and hypotension have resolved or are improving.
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DIAGNOSIS
Failure to consider that gastrointestinal and neurologic symptoms may be due to seafood poisoning is common.
TREATMENT
- Paralytic. Failure to anticipate respiratory paralysis and failure may lead to complications.
- Amnestic. Failure to anticipate pulmonary edema, dysrhythmias, and seizures may lead to unnecessary sequelae.
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ICD-9-CM 988.0Toxic effect of noxious substances eaten as food: fish and shellfish.
See Also: SECTION II, Hypotension, Seizure, and Ventricular Dysrhythmias chapters.
RECOMMENDED READING
Morris PD, Campbell DS, Taylor TJ, et al. Clinical and epidemiological features of neurotoxic shellfish poisoning in North Carolina. Am J Public Health 1991;81:471-474.
Sakamoto Y, Lockey RF, Krzanowski JJ. Shellfish and fish poisoning related to the toxic dinoflagellates. South Med J 1987;80:868-872.
Teitelbaum JS, Zatorre RJ, Carpenter S, et al. Neurologic sequelae of domoic acid intoxication due to ingestion of contaminated mussels. N Engl J Med 1990;322:1781-1787.
Author: Luke Yip
Reviewer: Richard C. Dart