DermatologistsBlog.com interview with Herbert B. Allen, MD
Professor and Chairman
Department of Dermatology
Drexel University College of Medicine
Dr. Allen: The main finding of our study was the elucidation of what precedes “the itch that rashes” that is atopic dermatitis (AD).
We have found that sweat ducts become occluded by biofilm made by staphylococci; this occlusion activates the innate immune system (TLR2). TLR2, in turn, has previously been shown to cause activation of PAR2 (the main pruritogen in AD) and TNFa (the main factor in producing spongiosis). In essence, AD is subclinical miliaria, as Dr. Sulzberger thought in 1947.
Dr. Allen: Unexpected findings: S. Aureus was twice as prevalent in lesional skin as was S. epidermidis; amyloid fibrils form the infrastructure of the biofilms; the genetics of the bacteria showed the presence of IcaD (36/40) and aap (1/40) genes. All 40 samples were shown to be capable of making biofilms, so there is at least one unidentified gene that also leads to biofilm production.
Dr. Allen: On occasion, it is possible to see a primary lesion in this disease: it is a small, flesh-colored papule or papulovesicle. (This represents the occluded duct and very early inflammation.)
Clinicians already do an excellent job at treating AD; but we have found that it is possible to prevent this disease by treating the stratum corneum kindly (less soap and hot water, less bathing, less scrubbing and more moisturizing). This addresses the patients’ genetic defects which oftentimes centers around filaggrin deficiency.
When necessary, antibacterial compounds, such as bleach baths, are preferable to antibiotics because these bacteria are normal flora and are already multidrug resistant.
Pathology specimens will show occluded ducts on routine staining giving specificity to “spongiotic dermatitis”. These occlusions will be PAS and Congo red positive.
Dr. Allen: We have looked at (and will be looking at) diseases that are known to be associated with eczema, namely Doucas Kapetenakis pigmented purpuric eruption and Meyerson’s nevus. We have also been evaluating diseases that have previously not been considered eczema that also have occluded ducts, such as seborrheic dermatitis, granular parakeratosis, and tinea pedis. The most unusual pruritic disorder that has occluded ducts is recent scabs or healing wounds: we have seen occluded ducts in that setting also. This indicates that “scabs that itch” have the same initial pathophysiology as eczema.