PERIPHERAL VASCULAR RESPONSES IN ATOPIC DERMATITIS. THE INFLUENCE OF ENVIRONMENTAL TEMPERATURE CHANGES

Vascular pattern of the palms--a clinical feature of atopic skin diathesis

BACKGROUND

Atopic skin diathesis is a clinical term to describe skin atopics with previous, present or future atopic eczema/dermatitis syndrome (AEDS). In clinical practice, an unequivocal assessment of atopic skin diathesis in non-eczematous patients may be difficult. The majority of the known clinical features included in diagnostic scores are characteristic, but not specific markers of atopy. Especially, the vasoreactivity of atopic skin is disturbed. This is manifested by white dermographism, an irregular vascular response to thermal stimuli, and paradoxic skin reactions to histamine, cholinergic agents, and nicotinates.

OBJECTIVE

The aims of our study were to investigate the clinical morphology of palmar vascular reactions in skin atopic and non-atopic individuals, and to determine whether this abnormal vascular reaction is more pronounced in skin atopic individuals.

METHODS

Forty persons, 20 of them skin atopics, assessed by the Erlangen Atopy Score and an elevated serum IgE level (>150 U/ml), were included in a prospective single-centre study. Standardized digital photographs of the palms were presented in a blinded manner to five dermatologists in random order by means of the computerized imaging analysis system KS400 3.0.

RESULTS

Evaluation of the original rgb (red, green, blue) color images and modified gray-level images showed that a pronounced reticular pattern of erythema of the palms was significantly (P < 0.0001) more common in skin atopics (72% and 69.6%, respectively).

CONCLUSION

The gross vascular pattern of the palm might be an additional diagnostic feature of atopy, and further studies are needed to establish its exact prevalence.

Skin levels of vasoactive intestinal polypeptide in atopic dermatitis

Atopic dermatitis (AD) can be exacerbated by various factors, including emotional stress, scratching and sweating. The aim of the present study was to evaluate the hypothesis that the inflammatory reaction in AD is also neurogenic. For this purpose, the levels of vasoactive intestinal polypeptide were measured radioimmunologically in whole-tissue homogenates of lesional skin of 13 patients with atopic dermatitis. Radioimmunoassay was performed using an antiserum, AH78, recognizing the carboxy-terminal fragment vasoactive intestinal polypeptide (22-28). Vasoactive intestinal polypeptide immunoreactivity was detected in relatively low amounts in control skin (0.428 +/- 0.08 pmol/g tissue), whereas a marked increase in the peptide was observed in lesional skin of patients with atopic dermatitis (5.62 +/- 1.25 pmol/g tissue). These results seem to suggest that vasoactive intestinal polypeptide could have a pathogenetic relevance in skin lesions of atopic dermatitis.

Pharmacophysiology of atopic dermatitis

Atopic dermatitis is clearly characterized by altered cutaneous physiologic responses. There is a tendency to acral vasoconstriction. Rubbing causes skin pallor and white dermographism. Vascular instability is demonstrated by responses to cholinergic agents, histamine, and nicotinates. Psychophysiologic studies demonstrate exaggerated vasodilator responses to emotional stress with consequent pruritus and scratching. The itch threshold is low, duration is prolonged, and nighttime scratching movements may be frequent or almost continuous. Regardless of the inciting trigger factors, the scratching causes the damage and the severe dermatitis. Thermal as well as emotional stimuli to sweating cause severe itching in AD, yet the concept of a miliaria-type, poral occlusion mechanism remains unproven. Some studies suggest actually increased sweating along with erythema and pruritus during acute flares of AD. The concept of sweat-borne allergens causing skin reactions during sweating is interesting but has never been proven. Studies of sweat responses to pharmacologic agents have produced conflicting data, and attempts to link these responses to Szentivanyi's beta-adrenergic blockade theory are not convincing. The numerous variables of climate, season, sex, age, and habitus affect sweating greatly. Future studies must carefully control for each of these factors before pharmacologically induced sweat responses can be interpreted clearly. A number of lines of evidence suggest involvement of histamine and other mediators in the evolution of erythema, pruritus, and scratching in AD. Flares of the condition have been reproducibly evoked by only two incitants: experimental emotional stress interviews and specific food challenge in selected sensitive individuals. In the latter, increased plasma histamine has been demonstrated, presumably generated by antigen/IgE stimulated degranulation of mast cells in the gut and/or skin. The demonstrated increased histamine releasability of basophils from atopic individuals may be the result of defective cellular regulatory mechanisms. Recent studies have demonstrated increased cyclic AMP-phosphodiesterase activity in leukocytes from atopic individuals. The resultant decreased intracellular cyclic AMP removes an inhibitory factor, which in turn causes net cellular hyperresponsiveness. This effect has been shown to account, at least in part, for increased histamine release from leukocytes of patients with AD. These and other studies focused upon cell functional regulation are providing better understanding of basic biochemical abnormalities and may lead to improved diagnostic and therapeutic approaches in managing atopic disease.