Skin reflectance-spectra and colour-value dependency on measuring-head aperture area in ordinary reflectance spectrophotometry and tristimulus colourimetry.

BACKGROUND/AIMS: Measurement of skin colour has become increasingly popular in the study of dermatology with the increased availability of portable instruments. However, different instruments have been reported as giving different results from measurement of the same skin region. The aim of this study was to examine the effects of differences in measuring-head aperture area on skin reflectance spectra and colour values. METHODS: We measured both reflectance spectra and CIE-L*a*b* values of the skin in five different anatomical regions on 10 subjects using two MINOLTA reflectance spectrometers that were identical apart from the aperture area of the measuring heads (diameters: 5 and 11 mm). For comparison, data were also obtained from a skin-coloured tile. RESULTS: Skin reflectance values measured with the wider-aperture instrument were higher than those measured with the other, irrespective of anatomical location. The differences between the two were near zero at an incident light wavelength of 400 nm, but increased to around 10% of the reflectance value at 700 nm, increasing exponentially with incident light of increasing wavelength. Skin colour was observed to be brighter, redder and yellower, in CIE-L*a*b* expression, when measured with the wider-aperture instrument. The differences between measurements obtained from the skin-coloured tile were much smaller. CONCLUSION: Skin reflectance and colour values measured with reflectance instruments are not absolute data but depend on the aperture area of the measuring head. This is probably due to variations in the proportion of longer-wavelength light reflected from the skin and collected by the instrument.

Localized heat urticaria: a clinical study using laser Doppler flowmetry.

We studied the pathophysiology of localized heat urticaria using laser Doppler flowmetry (LDF) in two patients with this rare disease. In heat challenge tests, performed with different challenge times and temperatures, a heat stimulator with a thermoregulated metal disc was utilized. Immediately after removal of the heat source, cutaneous blood flow (CBF) changes in the tested sites were monitored with LDF. In both patients the increase in (CBF) took place at some intervals after a heat challenge, synchronous with the start of the urticarial response. This interval, or the latency time (LT), showed distinct inverse proportion to the intensity of heat stimuli and was prolonged by effective treatments, such as application of antihistamines and repeated heat exposure by LDF. Therefore, the time of latency might be regarded as a good indicator of the severity of illness and therapeutic effectiveness, and thus might reflect the relationship between the degree of heat stimuli and the releasing process of chemical mediator(s) in patients with localized heat urticaria (LHU).

Severe dermographism after topical therapy with diphenylcyclopropenone for alopecia universalis.

We describe here a 19-year-old Japanese man with an 11-year history of alopecia universalis, who, after the 1st application of a 0.003% diphenylcyclopropenone (DPCP) solution to the whole scalp, developed acute contact dermatitis at the test site, together with widespread severe dermographism. Every 3 weeks, persistence of the severe urticarial reaction and efficacy of treatment were monitored by constant pressure stimuli in a series of pressure tests, and subsequently evaluated by laser Doppler flowmetry (LDF). Although, on pressure tests, the urticarial response was found to significantly improve after starting treatment, erythematous responses continued to appear for nearly 3 months. The persistent course of these side-effects in our patient strongly suggests that precautions must currently be taken in the therapeutic use of potent sensitizers such as DPCP.