Alterations in Brain Neural Network and Stress System in Atopic Dermatitis: Novel Therapeutic Interventions.

Atopic dermatitis is a common chronic inflammatory skin disease, with most cases experiencing skin barrier dysfunction and enhanced allergen entry, accompanied by cytokine production which evokes predominantly type-2-skewed immune responses, itch, and scratching behavior. Although intense itch and excessive scratching behavior affect progression of skin lesions, it is unclear what causes them. Data suggest that scratching behavior stimulates brain dopaminergic reward and habit learning systems, strengthening habitual scratching behavior, while nocturnal scratching behavior presumably increases locus coeruleus-noradrenergic system activity, prompting sleep disturbances. At the early stage of atopic dermatitis, increased cortisol levels, due to hypothalamic-pituitary-adrenal axis overactivation caused by such system stimulation, can induce dorsolateral prefrontal cortex disturbance with reinforcement of habitual scratching behavior and may aggravate type-2-skewed immune responses in the skin. During the later phases, whereas blunted hypothalamic-pituitary-adrenal axis function and the shift of type-2-dominated to type-1-co-dominated inflammation are induced, noradrenergic system overactivation-associated dorsolateral prefrontal cortex disruption is ongoing and responsible for itch cognitive distortion to catastrophize about itch, which leads to a vicious spiral along with habitual scratching behavior and skin lesions. Data are presented in this review indicating that while skin immune system dysfunction initiates pathologic changes in atopic dermatitis, brain neural network and stress system alterations can promote the progression of this condition. It is also suggested that cognitive distortion contributes to pathology in atopic dermatitis as with some psychiatric disorders and chronic pain. The proposed mechanistic model could lead to development of novel medications for slowing or terminating the relentless progression of this disorder. SIGNIFICANCE STATEMENT: Although conventional pharmacological interventions focusing on skin homeostasis and itch occurrence significantly attenuate clinical signs in atopic dermatitis patients, achievement of 100% improvement is less than 40% in several double-blind, randomized, placebo-controlled trials. Our model predicts that itch cognitive distortion, due to dorsolateral prefrontal cortex disturbance, can significantly contribute to the progression of atopic dermatitis and that agents capable of improving brain neural network, stress system, and skin homeostasis may be effective as interventions in the treatment of this condition.