Anaphylaxis DDx

Overview

Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction. It is characterised by rapidly developing life-threatening airway (pharyngeal or laryngeal edema) and/or breathing (bronchospasm and tachypnea) and/or circulation (hypotension and tachycardia) problems usually associated with skin and mucosal changes.

Causes of Anaphylaxis

Common

• Insect stings (most commonly honeybee, ants, wasps)
• Foods (most commonly peanuts, tree nuts, and seafood in adults; eggs, cows milk, dairy products, seeds, and fruit in children)
• Medications (most commonly antibiotics, non-steroidal anti-inflammatory drugs, contrast-induced anaphylactoid reactions, immunotherapy)
• Unidentified (no cause found, more than 50% of cases)

Uncommon

• Physical triggers (exercise, heat, cold, UV light)
• Biological fluids (transfusions, immunoglobulin, antivenoms, semen)
• Latex
• Tick bites
• Hormonal changes (breastfeeding, menstrual factors)
• Dialysis membranes (haemodialysis-associated anaphylaxis)
• Hydatid cyst rupture
• Aeroallergens (domestic/laboratory animals, pollen)
• Food additives (monosodium glutamate, metabisulfite, preservatives, colours, natural food chemicals)
• Topical medications (antiseptics)

Differential diagnosis of conditions that mimic anaphylaxis

• Tissue swelling
  • Idiopathic urticaria
  • Isolated angioedema
    • Idiopathic
    • Angiotensin-converting enzyme inhibitor-induced
    • Acquired or hereditary C1 esterase inhibitor deficiency
• Conditions mimicking upper airway oedema
  • Dystonic reactions mimicking symptoms of a swollen tongue
  • Acute oesophageal reflux (sudden onset of painful throat “swelling”)
• Flushing syndromes
  • Peptide-secreting tumours (eg, carcinoid syndrome, VIPomas)
  • Alcohol-related
  • Medullary carcinoma of thyroid
  • Red man syndrome (associated with vancomycin infusion)
• Neurological syndromes
  • Epileptic seizure
  • Stroke
• Other causes of collapse
  • Vasovagal episodes
  • Systemic inflammatory response syndrome
  • Shock due to other causes
• Acute respiratory distress
  • Asthma
  • Panic disorders
  • Globus hystericus
  • Laryngospasm
  • Vocal cord dysfunction
• Miscellaneous
  • Scombroid fish poisoning
  • Serum sickness
  • Phaeochromocytoma
  • Systemic mastocytosis

CCC Differential Diagnosis Series
NEURO	Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT	Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
LABS	LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,  HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,  ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes

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