Patch Test Relevance and Systemic Exposure Pathways in Eczema Patterns Suspected of Systemic Contact Dermatitis

Systemic contact dermatitis (SCD) occurs when sensitised individuals react to an allergen delivered systemically. Indian data that relate clinical patterns, patch-test relevance and systemic exposures are limited.

(i) Characterise the clinico-demographic profile of four eczema patterns historically linked to SCD-non-specific eczema, pompholyx, recalcitrant hand eczema and symmetrical drug-related intertriginous-flexural exanthema (SDRIFE), and (ii) map probable systemic exposure pathways for the six allergens selected a priori based on their relevance in Indian patch-test populations and their recognised or plausible systemic exposure pathways (para-phenylenediamine, nickel, parthenium, potassium dichromate, cobalt and Balsam of Peru).

We performed a prospective observational study at a tertiary care centre in North India from July 2023 to July 2024. Consecutive patients ≥ 12 years with the target eczema patterns underwent detailed exposure history, Indian Standard Series patch testing and COADEX grading. Diagnosis of SCD required a relevant positive patch test, documented systemic exposure and temporal flare correlation. Oral provocation was not performed. Descriptive statistics were performed, with exploratory categorical comparisons using chi-square or Fisher's exact tests, as appropriate.

One hundred patients (mean ± SD age 37.7 ± 14.7 years; 59% female) were enrolled. Clinical distribution was non-specific eczema 38%, pompholyx 32%, hand eczema 29% and SDRIFE-like eruption 1%. Patch tests were positive in 40%, and leading sensitisers were para-phenylenediamine 13%, nickel 9%, parthenium 9% and potassium dichromate 8%. Two women (2%; 95% CI 0.24%-7.04%) fulfilled the study's prespecified clinical criteria for SCD: one nickel-associated case classified as clinically definite and one garlic-associated case classified as probable. No SCD was diagnosed in pompholyx or hand eczema subgroups.

Although clinically relevant contact sensitisation is frequently observed, only two of 100 patients fulfilled the study's clinical criteria for SCD. These findings support targeted patch testing and structured exposure assessment in specific eczema patterns associated with SCD. Larger prospective multicentre studies are needed to refine criteria and capture the true burden of disease.