False-positive "poral" cobalt patch test reactions reside in the eccrine acrosyringium

Area of Science:

• Dermatology
• Toxicology
• Histopathology

Background:

• Cobalt is a metal used in various industries.
• Contact dermatitis is a common skin condition.
• Distinguishing irritant from allergic reactions is crucial for diagnosis.

Purpose of the Study:

• To investigate the nature of irritant reactions to cobalt observed during patch testing.
• To describe the unique histopathological features of these reactions.
• To differentiate these reactions from allergic contact dermatitis.

Main Methods:

• Patch testing of 222 patients in a contact dermatitis clinic (1993-1995).
• Detailed clinical observation of reactions to cobalt.
• Histopathological examination of skin biopsies from affected sites.

Main Results:

• Seventy (32%) of 222 patients exhibited irritant reactions to cobalt.
• Reactions were characterized as "poral", affecting the acrosyringium.
• Histopathology confirmed these reactions are neither follicular nor petechial and appear non-allergic.

Conclusions:

• Cobalt can induce unique "poral" irritant reactions.
• These reactions likely result from a direct toxic effect of cobalt on the acrosyringium.
• The findings aid in differentiating irritant cobalt reactions from allergic contact dermatitis.