Differentials
Food poisoning (other causes)
SIGNS / SYMPTOMS
Similar clinical presentation with gastrointestinal distress (nausea, vomiting, diarrhoea); usually suspected if multiple people develop symptoms after eating the same contaminated food or drink.
INVESTIGATIONS
Stool culture: isolation of specific pathogen.
Stool ova and parasite exam: isolation of specific ova and/or parasite.
Viral gastroenteritis
SIGNS / SYMPTOMS
Similar clinical presentation with gastrointestinal distress (nausea, vomiting, diarrhoea); absence of progressive muscle weakness and paralysis.
INVESTIGATIONS
Viral stool culture: positive for causative organism.
Anxiety/panic episode
SIGNS / SYMPTOMS
Similar clinical presentation; oral numbness and diffuse weakness; absence of progressive weakness.
INVESTIGATIONS
Arterial blood gases: respiratory alkalosis secondary to hyperventilation.
Cerebrovascular incident
SIGNS / SYMPTOMS
Difficulty with speaking and swallowing; focal weakness; altered mental status.
INVESTIGATIONS
CT brain without contrast: hyperattenuating lesion in haemorrhagic stroke; hypoattenuating (dark) lesion in ischaemic stroke, although may not show up within the first 24 to 48 hours of ischaemic stroke.
Botulism toxin exposure
SIGNS / SYMPTOMS
Similar clinical presentation with gastrointestinal distress (nausea, vomiting, diarrhoea); progressive muscle weakness, and paralysis.
INVESTIGATIONS
Mouse bioassay of serum, gastric secretions, stool, or food samples: identifies toxin of Clostridium botulinum.
Culture of food samples, gastric aspirates, or faecal material: identifies toxin of C botulinum.
Transverse myelitis
SIGNS / SYMPTOMS
Similar clinical presentation with progressive weakness; absence of gastrointestinal distress (nausea, vomiting, diarrhoea).
INVESTIGATIONS
Cerebrospinal fluid analysis: pleocytosis with modest number of lymphocytes and increase in total protein.
MRI shows focal demyelination with possible enhancement at the appropriate level.
Ciguatera toxin exposure
SIGNS / SYMPTOMS
Similar clinical presentation with gastrointestinal distress, oral numbness, and sensory symptoms in the extremities; cardiovascular symptoms; paraesthesias, dysaesthesias, and hyperaesthesias.
Food allergy/intolerance
SIGNS / SYMPTOMS
History of exposure to certain foods known to cause intolerance or allergies (milk, lactose, gluten) and relapsing symptoms with challenge; angio-oedema of the face and pharynx, bronchospasm, urticaria.
INVESTIGATIONS
Coeliac markers are positive in most patients with gluten intolerance.
Hydrogen breath test helps in diagnosing lactose intolerance.
Colonoscopy and biopsies help in diagnosing milk allergies.
Tick paralysis
SIGNS / SYMPTOMS
Similar clinical presentation with progressive muscle weakness and paralysis; absence of gastrointestinal distress (nausea, vomiting, diarrhoea); history of tick exposure.
INVESTIGATIONS
No differentiating tests; diagnosis is clinical.
Guillain-Barre syndrome
SIGNS / SYMPTOMS
Similar clinical presentation with progressive muscle weakness and paralysis; absence of gastrointestinal distress (nausea, vomiting, diarrhoea).
INVESTIGATIONS
Nerve conduction studies: slowing of nerve conduction velocities.
LP: elevated cerebrospinal fluid protein, normal/slightly high lymphocytes (< 50 cells/mm³).
LFT: elevated AST and ALT as high as 500 U/L; bilirubin may be transiently elevated but rarely high enough to cause jaundice.
Myasthenia gravis
SIGNS / SYMPTOMS
Similar clinical presentation with progressive muscle weakness and paralysis; absence of gastrointestinal distress (nausea, vomiting, diarrhoea).
INVESTIGATIONS
Serum anti-acetylcholine receptor (anti-AChR) antibody analysis: titre above a certain point (varies with assay used).
Anti-muscle-specific tyrosine kinase (MuSK) antibodies: may be positive.
Electrolyte abnormalities
SIGNS / SYMPTOMS
Similar clinical presentation with circumoral numbness, paraesthesias in the extremities, weakness, hypocalcaemia, or hypokalaemia.
INVESTIGATIONS
Serum electrolytes: abnormal values.
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