What is the diagnosis and treatment for scombroid poisoning?

Diagnosis and Treatment of Scombroid Poisoning

Diagnosis

Scombroid poisoning should be suspected in any patient presenting with histamine-like symptoms (flushing, urticaria, headache, gastrointestinal complaints) that develop within minutes to hours after consuming fish, particularly tuna or other dark-meat fish species. 1, 2

Clinical Presentation

The diagnosis is primarily clinical, based on characteristic symptoms and temporal relationship to fish consumption:

• Cutaneous manifestations are the most common presenting features, including flush (often sunburn-like rather than typical urticaria), pruritus, and erythematous rash affecting the face and trunk 1, 3, 4
• Gastrointestinal symptoms occur in approximately 37% of cases, including nausea, vomiting, abdominal cramps, and diarrhea 2, 5
• Neurological symptoms include headache (30% of cases), dizziness, and blurred vision 2, 6
• Cardiovascular manifestations such as palpitations and hypotension can occur in approximately 25% of cases, though severe complications are infrequent 2, 5

Key Diagnostic Features

• Rapid onset: Symptoms typically develop within 20 minutes in 65% of patients, though can occur up to several hours post-ingestion 2
• Fish species: Tuna is implicated in approximately 85% of cases, though other scombroid and non-scombroid dark-meat fish can be involved 2, 6
• Multiple victims: Often affects more than one person who consumed the same fish 1, 6
• Normal serum tryptase levels: This distinguishes scombroid poisoning from true anaphylaxis 1

Laboratory Confirmation

• Histamine measurement in the implicated fish flesh (levels >50 mg/100g are diagnostic) or in patient's plasma can confirm the diagnosis 3, 6
• However, treatment should not be delayed while awaiting laboratory confirmation 6

Treatment

The mainstay of treatment is oral H1-antihistamines, with most cases resolving completely within 12-24 hours with supportive care alone. 2, 4, 5

Immediate Management

• Administer H1-antihistamines as first-line therapy (used in 65% of cases with good response) 2, 4
• Provide intravenous fluids for patients with hypotension or significant gastrointestinal losses 2
• Monitor vital signs closely, as approximately 25% of patients develop abnormal vital signs including hypotension 2

Additional Interventions

• H2-antihistamines may be added for refractory symptoms, though evidence is limited 4
• Bronchodilators should be administered if bronchospasm develops 4
• Vasopressor support may be required in rare cases of severe hypotension 2

What NOT to Do

• Do not routinely administer corticosteroids or epinephrine unless there is true anaphylaxis from a concurrent fish allergy 2
• Do not induce emesis as this provides no benefit and may delay appropriate care 6
• Do not administer activated charcoal unless specifically advised by poison control, as it is generally ineffective for this toxin 6

Critical Differential Diagnosis

Distinguish scombroid poisoning from true IgE-mediated fish allergy by the presence of tachycardia (rather than bradycardia), involvement of multiple people eating the same fish, and normal serum tryptase levels. 1, 2

• Vasovagal reactions typically present with bradycardia and pallor, lacking the characteristic cutaneous manifestations 1
• True fish allergy would show elevated serum tryptase and typically affects only the allergic individual 1
• Other causes of flushing (carcinoid syndrome, pheochromocytoma) lack the temporal relationship to fish consumption 1

Observation and Follow-up

• Prolonged observation may be required as severe toxicity can develop even after initial mild presentation 2
• Most patients experience complete resolution within 12-24 hours without sequelae 5, 6
• Notify public health authorities immediately to prevent additional cases and trace the contaminated fish source 2, 6

Common Pitfalls

• Misdiagnosis as allergic reaction: Five patients in one series were inappropriately treated with corticosteroids and epinephrine due to misdiagnosis 2
• Underrecognition: Scombroid poisoning is one of the most common fish-related poisonings worldwide but remains underdiagnosed by physicians 3, 4
• Assuming only scombroid fish are implicated: Non-scombroid dark-meat fish can also cause this poisoning 6