In a case-control study, researchers confirmed that intraepidermal Langerhans cell collections are the histopathologic feature most specifically associated with allergic contact dermatitis.

The study included 170 skin biopsies from patients evaluated with patch testing and clinical correlation. Among these, 111 cases (65%) were classified as allergic contact dermatitis (ACD) based on clinically relevant positive patch test results, and 59 cases (35%) were classified as non-ACD.

Langerhans cell collections were observed in 26% (29/111) of ACD cases compared with 12% (7/59) of non-ACD cases, a statistically significant difference (P = .03). Logistic regression analysis, controlling for age and sex, showed that the presence of Langerhans cell collections was associated with an increased likelihood of ACD.

In contrast, heavy dermal eosinophilic infiltration—defined as more than 100 extravascular eosinophils per five high-power fields—was significantly more common in non-ACD cases (18%, 11/59) than in ACD cases (7%, 8/111) (P = .02). The presence of at least one dermal eosinophil was nearly universal in both groups (69% of ACD cases and 68% of non-ACD cases), indicating that the presence of eosinophils alone is not specific to ACD.

“This largest study to date is the first to independently confirm Langerhans cell collections as the single histopathologic feature most closely associated with allergic contact dermatitis,” said senior author Peggy A. Wu, MD, MPH, of the Department of Dermatology at the University of California, Davis in the Journal of the American Academy of Dermatology.

The cohort had a median age of 63 years (IQR, 48–71 years), and 68% were female. The median duration of rash prior to biopsy was 10 months (IQR, 3–36 months).

The findings suggest that while spongiotic dermatitis encompasses a broad range of clinical diagnoses, the presence of Langerhans cell collections within spongiotic vesicles—defined as vesicles in which Langerhans cells are the predominant inflammatory cell—may aid in distinguishing ACD from other etiologies. Other histopathologic features, such as eosinophilic spongiosis and multinucleated dermal dendritic cells, were not significantly different between groups.

Although limited by its retrospective design and small validation sample, this study provides additional evidence for the diagnostic utility of Langerhans cell collections in ACD and calls into question the specificity of dermal eosinophils as a marker for the disease.

The authors disclosed no conflicts of interest.