Cholinergic urticaria: acetylcholine-receptor-dependent immediate-type hypersensitivity reaction to copper

Area of Science:

• Immunology
• Dermatology
• Neuroscience

Background:

• Cholinergic urticaria syndrome (ChUS) is a hypersensitivity reaction often triggered by stimuli like exercise, heat, or emotion.
• The exact mechanisms underlying ChUS, particularly receptor-level changes and co-existing sensitivities, require further elucidation.

Observation:

• A patient diagnosed with ChUS presented with an unusually high density of muscarinic cholinergic receptors at affected skin sites.
• A 48-hour contact patch test for copper, followed by an exercise challenge, revealed a previously undetected sensitivity to copper.

Findings:

• The amplified muscarinic receptors likely contribute to the patient's exaggerated response to acetylcholine release.
• Exercise-induced histamine release from mast cells, triggered by acetylcholine, appears to be the primary mechanism for punctate urticaria in this case.
• The exercise challenge post-patch test demonstrated a localized urticarial reaction at the copper patch test site, indicating an antigen-potentiated cholinergic response.

Implications:

• These findings suggest that increased muscarinic receptor expression is a potential factor in the pathophysiology of ChUS.
• The development of "cholinergic patch testing" offers a novel diagnostic method for uncovering occult sensitivities that exacerbate acetylcholine-mediated reactions.
• This approach may be valuable for identifying other instances where antigens enhance acetylcholine-induced hypersensitivity reactions.