Arthus Reaction

Question 1

What type of hypersensitivity reaction is an Arthus reaction?

Answer 1

A localised Type III hypersensitivity reaction caused by deposition of antigen–IgG immune complexes in small vessel walls.

Question 2

What is the pathophysiology of an Arthus reaction?

Answer 2

Occurs in individuals with high circulating IgG; re-exposure to antigen leads to local immune complex formation, complement activation, neutrophil recruitment, and release of enzymes/free radicals causing vasculitis, oedema and tissue necrosis.

Question 3

When does an Arthus reaction typically develop after antigen exposure?

Answer 3

Within 4–12 hours after antigen exposure such as vaccination or injection of an antigen to which the patient already has high antibody levels.

Question 4

What are the clinical features of an Arthus reaction?

Answer 4

Localised pain, swelling, erythema, warmth, induration, and in severe cases blistering, ulceration or tissue necrosis.

Question 5

What are examples of situations where an Arthus reaction may occur?

Answer 5

Following booster vaccinations (tetanus, diphtheria, pneumococcal), after therapeutic protein or antitoxin injections such as antivenom, and in experimental skin testing with foreign proteins.

Question 6

How is an Arthus reaction managed?

Answer 6

It is generally self-limiting; management is supportive with analgesia, cool compresses, elevation and avoidance of repeat antigen exposure until antibody levels fall.