Sensitive skin can be small fibre neuropathy: results from a case-control quantitative sensory testing study.

BACKGROUND: Sensitive skin syndrome (SSS) is defined as the occurrence of unpleasant sensations (itch, pain, burning, prickling) in response to stimuli that should not normally cause such sensations. Previous studies show that SSS could be a small fibre neuropathy, but quantitative sensory testing (QST) is lacking. OBJECTIVES: Using QST, to determine the presence or absence of tactile sensitivity disorder, mainly heat pain threshold (HPT), in patients with SSS. METHODS: This monocentric case-control study included 21 patients with SSS and 21 controls. The patients underwent QST. Neuropathic pain was assessed by two questionnaires: the Douleur Neuropathique 4 (DN4) and the Neuropathic Pain Symptom Inventory (NPSI). RESULTS: Forty-two patients were included in the study. The HPT was significantly lower in the cases (14·5 ± 2·8) than in the controls (17·8 ± 2·5) (P < 0·001). Intermediate pain (HPT 5·0) was also significantly decreased in patients with SSS. The DN4 and NPSI scores were significantly higher in the cases than in the controls. CONCLUSIONS: The decrease in HPT in patients with SSS compared with controls suggests the presence of hyperalgesia, probably due to the damage of C-fibres. These findings, as well as the increased DN4 and NPSI scores, strengthen the neuronal hypothesis of SSS and are new arguments for consideration of SSS as small fibre neuropathy.

Aggregate exposure to common fragrance compounds: Comparison of the contribution of essential oils and cosmetics using probabilistic methods and the example of limonene.

The knowledge of aggregate exposure to different types of products is paramount in the risk assessment. The aim of this study was to compare the relative contribution of essential oils compared to cosmetics on the daily dermal exposure to limonene, an ubiquitous fragrance compound that can be an allergen depending on its degree of oxidation. Aggregate daily exposure to limonene was calculated among a panel of French volunteers using both essential oils and cosmetics, for 4 different specific zones, i.e. face and neck, chest, upper limbs and lower limbs. Calculations were made using a probabilistic Monte Carlo method and sensitivity analysis. The main strength of this work was the inclusion of essential oils in addition to cosmetics in the model. For the first time, the generated data could be used to compare the contribution of these two products in dermal exposure. Essential oils appear to be significant contributors to exposure to limonene particularly for the face. This work is a first step that will permit to determine the exposure to other fragrance compounds with sensitizing potential. These data will be useful for risk managers to consider the inclusion of essential oils in the overall burden of this pathology.

Consumption of hair dye products by the French women population: Usage pattern and exposure assessment.

Only few published data are available in the literature about consumption and exposure, for hair dye products. The aim of this study was to assess the use of 10 different hair dye products in French Women with a focus on consumption of hair dye in different places of use (at home and at the hairdressers) in order to assess the corresponding dermal exposures. The assessment was performed on a total of 4237 women older than 15 years old, thanks to three national web surveys. The percentage of hair dye users among the French women population was about 64%.The mean frequency of use ranged between 2.23 and 14.22 times per year depending on the studied product and age category of women. This study provided the first data available for exposure to hair dye products with mean exposures ranging between 1.48 and 6.49 mg/kg bw/day depending on the product studied and age category of women. Moreover, consumption data obtained in this study might be useful to perform safety assessment of hair dye products thanks to the knowledge of the age categories of the population having the highest percentage of users and/or frequency of use.

Laminar distribution of neurons in extrastriate areas projecting to visual areas V1 and V4 correlates with the hierarchical rank and indicates the operation of a distance rule.

The directionality of corticocortical projections is classified as feedforward (going from a lower to higher hierarchical levels), feedback (interconnecting descending levels), and lateral (interconnecting equivalent levels). Directionality is determined by the combined criteria of the laminar patterns of the axon terminals as well as the cells of origins and has been used to construct models of the visual system, which reveals a strict hierarchical organization (Felleman and Van Essen, 1991; Hilgetag et al., 1996a). However, these models are indeterminate partly because we have no indication of the distance separating adjacent levels. Here we have attempted to determine a graded parameter describing the anatomical relationship of interconnected areas. We have investigated whether the precise percentage of labeled supragranular layer neurons (SLN%) in each afferent area after injection in either visual areas V1 or V4 determines its hierarchical position in the model. This shows that pathway directionality in the Felleman and Van Essen model is characterized by a range of SLN% values. The one exception is the projection of the frontal eye field to area V4, which resembles a feedforward projection. Individual areal differences in SLN% values are highly significant, and the number of hierarchical steps separating a target area from a source area is found to be tightly correlated to SLN%. The present results show that the hierarchical rank of each afferent area is reliably indicated by SLN%, and therefore this constitutes a graded parameter that is related to hierarchical distance.

Area-specific laminar distribution of cortical feedback neurons projecting to cat area 17: quantitative analysis in the adult and during ontogeny.

Corticocortical pathways can be classified as feedback and feedforward, in part according to the laminar distribution of the parent cell bodies. Here, we have developed exhaustive sampling procedures to determine unambiguously this laminar distribution. This shows that individual extrastriate areas in the adult cat have highly stereotyped proportions of supragranular layer neurons with respect to the total population of neurons back-projecting to area 17. During development, these adult laminar patterns emerge from an initially uniform radial distribution through a process of selective reorganization, which is highly specific to each area. Injections of fluorescent retrograde tracers were made in area 17. In areas 19, 20, posteromedial lateral suprasylvian area, and anteromedial lateral suprasylvian area, we defined a projection zone as the region containing retrogradely labeled neurons. In the neonate, counts of labeled neurons throughout the projection zones show constant percentages of 40% in the supragranular layers. During development, there is an area-specific reduction in the percentage of supragranular labeled neurons generating the laminar distributions characteristic of each area. Numbers of labeled neurons were estimated at different eccentricities of the projection zone. This finding indicates that during development there is a relative decrease in the numbers of labeled neurons of the periphery of the projection zone in the supragranular layers but not in the infragranular layers. This decrease is accompanied by a relative decrease in the dimensions of the supragranular projection zone with respect to the infragranular projection zone. These findings suggest that each extrastriate area precisely adjusts the proportions of supragranular layer neurons back-projecting to striate cortex in part by developmental changes in the divergence-convergence values of individual neurons. This shaping of corticocortical connectivity occurs relatively late in postnatal development and could, therefore, be under epigenetic control.