• atopic dermatitis
• allergic contact dermatitis
• target therapy

Background: Atopic dermatitis (AD) is a chronically relapsing skin inflammatory
disorder. The disease is linked to a defect in the skin barrier and a dysregulation of
innate and adaptive immunity, in particular the type 2 inflammatory response.
Clinical hallmarks are an intense itching and inflammatory eczematous lesions up
to lichenification (thickening of the stratum corneum epidermis) in more advanced
stages, with a strong impact on the patient's quality of life. Allergic Contact
Dermatits (ACD) is a skin disease resulting from a reaction of the immune system
to low-molecular-weight organic chemicals or metal ions. ACD is usually divided
into two phases: the sensitization starts with hapten penetration through stratum
corneum and the subsequent activation of dendritic cells of the skin, which migrate
to the regional lymph nodes to present the neo-antigen toTh1 lymphocytes (CD4+
and CD8+). In sensitized individuals, the following contact with the allergen causes
rapid and strong recruitment of T-lymphocyte in the skin that release
proinflammatory cytokines (such as TNF, IFN-ỵ, IL-4, IL-5, IL-13, IL-17, IL-12, IL-22,
IL-23) able to activate the resident cells, and to induce apoptosis of keratinocytes
with resulting spongiosis and/or vesiculation. Clinically in acute phase there are
eczematous wet skin lesions and in chronic phase dull red, scaly, and lichenified
lesions in the absence of significant differences from AD. The clinical and
histological differential diagnosis of these two diseases is therefore very complex.
Objectives: We conducted a prospective longitudinal case-control study with the
aims of 1- analyze correlations between AD and ACD in terms of gender, age,
smoking, family history, disease severity, IgE positivity, age of disease onset,
association with atopic march, itch score, Eczema Area Severity Index (EASI) score
and comorbidities in order to implement data on the relationship between AD and
ACD to improve outpatient management; 2- analyze peculiar cytokines and
chemokines expression in lesional skin of AD and ACD by PCR arrays for a better
characterization of inflammation and development of possible new therapeutic
strategies; 3- evaluate of prognostic clinical and molecular biomarkers of treatment
response in moderate-to-severe AD.
Materials and methods: We recruited 134 patients including 90 patients with
moderate-severe AD (selected on the Eczema Area Severity Index≥ 24), 32 with
moderate-severe AD and concomitant ACD, and 12 patients with ACD from January
2020 to June 2022. Patients enrolled were subjected to patch test (to discriminate
any concomitant contact allergies) ; dosage of specific blood biomarkers such as
IgE, eosinophils, LDH and tryptase (in patients with elevated IgE tot, specific IgE
was assayed and molecular diagnostics of allergenic proteins was performed) ;
clinical evaluation (Investigator Global Assessment, EASI, NRS itch and NRS
sleep); allergological, otolaryngological and/or pneumological evaluation for a more
specific characterization of atopic comorbidities.
On selected patients we performed under local anesthesia 5-mm punch biopsy on
lesional skin (patients naive to therapy or in washout for at least 2 weeks from
topical therapy and 4 weeks from systemic therapy) to analyze cytokine and
chemokine expression. The samples were cryofrozen to - 70 degrees after
immersion in RNA later for subsequent RNA extraction, cDNA conversion and
analysis by use of PCR arrays (Qiagen RT2 focus panel).
Patient data were entered into an Excel database and subjected to statistical
analysis with SPSS V.28 technology. Relative to gene expression data, we used
the Qiagen program at the link https://dataanalysis2.qiagen.com/Quantinova.
Results: We found that the prevalence of ACD is lower than AD (9% vs 67%) with
concurrence of both forms in 24% of patients configuring ACD as an important
comorbidity of AD and justifying the important similarities in the literature between
the two forms. Impact analysis of other variables on the onset of ACD in AD
patients, such as sex, age, smoking, family history of atopy, onset of AD, disease
severity, presence of pruritus, and comorbidities, did not result in finding statistically
significant associations. Regarding genetic analysis of cytokines and chemokines in
lesional skin of AD and ACD by PCR arrays we found an up regulation of IL-23A,
STAT1 and TNF gene expression in ACD patients compared to AD.
Among the 80 variables analyzed on moderate-to-severe AD in order to assess the
impact of clinical and molecular differences of individual patients on response to
therapy an high IgE values and psoriasiform clinical phenotype were found to be a
negative prognostic factor of response to therapy while female sex was a positive
prognostic factor of response to therapy.
Relative to the gene expression of 10 classic atopic dermatitis and 7 atopic
dermatitis variants (1 head and neck, 3 prurigo, 2 psoriasiform dermatitis, 1
nummular eczema) assessed by PCR array, we found increased expression of
IL-23A in the nummular eczema phenotype, markedly increased expression of IL-4
and IL 17-A in the prurigo nodularis phenotype and increased expression of IL-13 in
the psoriasiform phenotype.
Conclusions: AD and ACD are both common skin diseases with an immune
pathogenesis and multiple factors influencing their association. Our study highlights
that ACD is a relevant comorbidity of AD rather than a distinct entity, with an
important impact on prognosis. Another relevant finding that emerged is that adult
atopic dermatitis is an extremely heterogeneous condition and presents an
intriguing diagnostic and therapeutic challenge for the dermatologist. The response
of the different clinical variants to current approved biologic therapy is fairly
reproducible except for the psoriasiform phenotype. Molecular characterization of
different clinical phenotypes forward-looking on the availability of new drugs for
treatment will allow tailoring therapy, with maximization of efficacy and reduction of
adverse effects of treatment.