Shellfish Toxicity Clinical Presentation

Updated: Dec 28, 2015
  • Author: Thomas C Arnold, MD, FAAEM, FACMT; Chief Editor: Asim Tarabar, MD  more...
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All 4 shellfish syndromes can produce symptoms lasting from a few minutes to several hours after ingestion of contaminated shellfish.

  • Paralytic shellfish poisoning
    • The onset generally is noted with paresthesias of the lips, tongue, and gums. Symptom onset usually occurs within 30 minutes of ingestion.
    • Symptoms at onset rapidly progress to involve the distal extremities.
    • Other symptoms include a sensation of floating, headache, ataxia, muscle weakness, paralysis, and cranial nerve dysfunction.
    • Gastrointestinal symptoms are less common and may include nausea, vomiting, diarrhea, and abdominal pain. Fatalities are usually within the first 12 hours of symptom onset and are caused by unsupported respiratory failure.
    • PSP usually lasts 3 days, but muscle weakness may persist for weeks.
  • Neurologic shellfish poisoning
    • The illness encountered with NSP is milder than that with PSP. Symptom onset ranges from 15 minutes to 18 hours postingestion, and the duration of toxicity ranges from 1-72 hours (usually < 24 h) postingestion.
    • Presenting symptoms include gastroenteritis; rectal burning; paresthesias of the face, trunk, and limbs; myalgias; ataxia; vertigo; and reversal of hot/cold sensation.
    • Other less common features include tremor, dysphagia, bradycardia, decreased reflexes, and mydriasis.
    • This syndrome presents much like ciguatera poisoning but without a paralytic component, and it may last from several hours to a few days.
    • The brevetoxins, unlike the other shellfish toxins, can become aerosolized by the surf and produce an allergic response characterized by rhinorrhea, conjunctivitis, bronchospasm, and cough in sensitive individuals along the shore.
  • Diarrheal shellfish poisoning
    • DSP is most common in Japan and Europe.
    • Gastroenteritis develops shortly after ingestion and generally lasts 1-2 days.
  • Amnestic shellfish poisoning
    • The only reported outbreak occurred in 1987 and affected more than 100 people after eating mussels harvested off Prince Edward Island, Canada.
    • Gastroenteritis followed by headache and short-term memory loss occurred.
    • In a few cases, severe cognitive dysfunction to the point of interfering with the patient's ability to perform normal daily activities was noted.
    • Seizures, coma, hemiparesis, and ophthalmoplegia were noted in the most severe cases. The mortality rate is 3%.


See the list below:

  • Findings vary according to the syndrome involved.
    • Gastrointestinal symptoms occur less often in PSP than in the other syndromes.
    • Paresthesias of the face and extremities are noted only in PSP and NSP.
    • ASP is the only shellfish syndrome with cognitive dysfunction as an early finding.
  • Volume depletion from gastrointestinal symptoms is common to all syndromes.


Ingestion of raw or cooked mollusks that contain the toxin in sufficient quantities ensures the development of symptoms.