Hairless guinea pig skin: anatomical basis for studies of cutaneous biology.

In order to characterize the microscopic anatomy of hairless guinea pig (HL-GP) skin, we utilized light microscopy with a computer-assisted image analysis system, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM revealed that the hair shafts of HL-GPs were thin, short, extremely irregular in diameter and often twisted and curled. The HL-GP epidermis was of similar thickness to that of human skin with distinct strata, serrated/non-serrated basal keratinocytes and shallow dermal papillae. The density of Langerhans cells in epidermal sheets, visualized by adenosine-s-triphosphatase staining, was similar to that of normal-haired guinea pigs (HD-GPs), although the dendrites of HL-GPs were thicker and shorter than those of HD-GPs. The dermal vasculature of HL-GPs was well-developed and similar to that of humans, demonstrating a network of vertically oriented capillary loops. HL-GPs had significantly more dendritic or spindle-shaped dermal interstitial cells than humans and HD-GPs. Collectively, these data suggest that HL-GP skin is more similar to human skin than to the skin of HD-GPs and other rodents and, therefore, the HL-GP may be a useful animal for studying cutaneous biology, experimental pathology, pharmacology and toxicology.

Sonography of the skin at 100 MHz enables in vivo visualization of stratum corneum and viable epidermis in palmar skin and psoriatic plaques.

A main drawback of 20-25 MHz ultrasound units for skin imaging is their limited resolution. We used a transducer with a center frequency of 95 MHz and a resolution of 8.5 microm axially and 27 microm laterally - an almost 10-fold increase compared with 20 MHz. By means of a new scanning technology we reached a depth of field of 3.2 mm. We examined normal palmar skin, normal glabrous skin on the abdomen, the upper back, the calf and the dorsal forearm, and 35 lesions of psoriasis vulgaris. From 11 psoriatic plaques biopsies were taken for correlation with the sonograms. In normal palmar skin, the horny layer is represented as an echopoor band below the skin entry echo, traversed by echorich coils, which correspond to eccrine sweat gland ducts. The thickness of this band significantly increases after occlusive application of petrolatum. Its lower border is defined by an echorich line, representing the stratum corneum/stratum Malpighii-interface. Underneath, a second echopoor band is visible, which corresponds to the viable epidermis plus the papillary dermis, bordered by the scattered echo reflexes of the reticular dermis. This band is also visible in glabrous skin; however, the stratum corneum cannot be detected. In psoriatic lesions, the thickened horny layer appears echorich; after application of petrolatum, its echodensity decreases. Below, the acanthotic epidermis plus the dermis with the inflammatory infiltrate are represented as an echopoor band. There is an excellent correlation between the sonometric thickness of this band and the histometric thickness of the acanthosis plus the infiltrated dermis. Our results show that 100 MHz sonography is a valuable tool for in vivo examination of the upper skin layers.

Quantification of vascular dysregulation in atopic dermatitis using laser Doppler perfusion imaging.

BACKGROUND/AIMS: The reactivity of cutaneous microcirculation to prostaglandin liberators and histamine has a wide variation in man. Especially patients with atopic dermatitis show frequently altered reactions like the paradox anemic reaction to nicotinic acid esters and the abnormally weak reaction to intracutaneous histamine injection. We wanted to investigate the reproducibility and sensitivity of two-dimensional laser Doppler perfusion imaging (LDPI) in quantifying these phenomena. METHODS: To study the reproducibility of LDPI, we measured the reaction to intracutaneous histamine injection and to application of nicotinic acid ester ointment at different time points and in contralateral body areas in 25 people with normal skin. In a second step, these stimuli were applied in 27 patients with atopic dermatitis and 23 normal controls in order to see whether LDPI is able to detect differences in the cutaneous vascular reaction between both groups. RESULTS: We found an excellent reproducibility of the parameters of LDPI measurements with regard to different locations (0.847≤r≤0.948) and time points (0.686≤r≤0.935). After epicut-aneous application of nicotinic acid ester, there were significant smaller flow values in the marked center of the reaction in patients with atopic dermatitis compared to the control group. This corresponded to the paradox anemic reaction seen clinically in 15 of 27 patients. After intracutaneous injection of histamine, patients with atopic dermatitis showed significantly higher flow values in the center of reaction than normal controls because whealing was markedly reduced. CONCLUSIONS: LDPI proved to be a reproducible and sensitive method for the follow-up of vascular reactions.

A model to assess the efficacy of moisturizers--the quantification of soap-induced xerosis by image analysis of adhesive-coated discs (D-Squames).

Clinical grading of dry skin syndromes (xerosis) is beset by many variables which limit its reliability. Removing scales onto adhesive coated discs (D-Squames) has provided a means for objective measurement of xerotic states. Using image analysis we have modified the basic procedure to assure greater accuracy and reproducibility. The distribution of grey values on the discs was determined, from which a single value of the degree of scaling was calculated. We term this the scaling index. To induce xerosis, the lower legs of 22 women, aged 26-64, were washed daily for 10 days with soap. After washing, one side received a moisturizing lotion, the other served as an untreated control. At specified intervals, scaling was graded clinically, electrical conductance was measured and D-Squames were obtained. On the moisturizer-treated legs there was a significant decrease in dryness grades and scaling indices at all time points. Conductance was significantly increased on days 8 and 11. The untreated washed legs showed no changes in clinical grades, although conductance significantly decreased and the scaling indices increased in the last stage of the study. D-Squame analysis unequivocally revealed the beneficial effect of a moisturizer on soap-induced xerosis and the expected increase in scaliness without treatment.

Improved resolution of magnetic resonance microscopy in examination of skin tumors.

Magnetic resonance imaging has become increasingly important for visualization and tissue differentiation of internal organs. Because of limited resolution, investigation of skin has been of little diagnostic value so far. We combined a homogeneous magnetic field of 9.4 T, as used in magnetic resonance spectroscopy, with gradient fields of 11.7 G/cm and an imaging unit to obtain a voxel resolution of 40 x 40 x 300 microm(3). With this magnetic resonance microscopy unit, we studied normal skin, 12 nevocellular nevi, 20 basal cell carcinomas, 8 melanomas, and 8 seborrheic keratoses after excision in vitro. The specimens were visualized in spin-echo images. The proton relaxation times T1 and T2 were determined for the different skin layers and tumor tissues. Interpretation of the spin-echo images was based on comparison with the correlating histology. Epidermis, dermis, subcutaneous tissue, and hair follicle complexes could be distinguished. Stratum corneum and hairs emitted no signal. All tumors presented as distinct, signal-rich, homogeneous structures within the dark, signal-poor dermis. Their shape corresponded to their outline in the histologic sections. Buds of superficial basal cell carcinomas could be resolved. The proton relaxation times T1 and T2 were significantly different among all skin layers and tumors. Our results demonstrate that with sufficient resolution, differentiation of skin tumors is possible using magnetic resonance imaging.