If atopic dermatitis is an atopic disease, why does it only proceed to asthma and allergic rhinitis in 30 and 35% of cases, respectively?(Williams, NEJM 2005) And why would an allergic disease tend to present at areas of friction or moisture, the extensor surfaces in babies (the friction is from crawling) and in flexural areas in adults? Or the somewhat peculiar hands and feet eczema?
Atopic dermatis is now believed to be a disease of the epidermal barrier. Breaches in the skin can introduce allergens that secondarily produce an atopic response. This understanding offers much better explanatory power, and helps make sense of the disparate bedside findings. For example, hand eczema is often provoked by occupational hazards, such as the wet hands of one who works for a restaurant. It also explains why eczema patients have dry skin – the epidermal integrity is breached, and water loss occurs.
One of the key findings in atopic dermatitis is pruritus. It has been called not an eruption that itches but an itch that erupts.
Here are a number of additional findings:
Itch when sweating
Intolerance to wool and lipid solvents
Hyperkeratosis, palmar hyperlinearity
Take Home Points:
Atopic dermatitis is a disease of the epidermal barrier
Pruritus is the hallmark
The distribution reflects vulnerabilities to epidermal breakdown (eg friction and moisture)