Long Lasting Allergic Patch Test Reactions: A Literature Review.

Area of Science:

• Dermatology
• Immunology
• Allergology

Background:

• Long-lasting allergic patch test reactions (LLAPTR) are characterized by palpable erythema persisting for ≥14 days post-allergen application.
• LLAPTR occur with various contact allergens, including those in standard baseline series.
• These reactions are not rare, observed in up to 17.9% of positive baseline patch tests.

Purpose of the Study:

• To investigate the occurrence and characteristics of long-lasting allergic patch test reactions (LLAPTR).
• To explore potential pathomechanisms and associated host factors for LLAPTR.

Main Methods:

• Analysis of clinical data from patients undergoing patch testing.
• Identification of reactions with prolonged erythema beyond the standard observation period.
• Review of literature on LLAPTR and associated factors.

Main Results:

• LLAPTR can persist for months, with gold salts being a frequent inducer.
• Hypothesized pathomechanisms include constant antigen stimulation or impaired immune down-regulation.
• Associated host factors may include strong initial reactions, older age, and atopy; no significant sex differences were noted.

Conclusions:

• LLAPTR represent a significant proportion of positive patch test reactions.
• Further research is needed to elucidate the precise pathomechanisms of LLAPTR.
• Understanding LLAPTR can improve diagnosis and management of allergic contact dermatitis.