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Year : 1990  |  Volume : 56  |  Issue : 5  |  Page : 367-370

Measurement of some biophysical parameters in skin lesions of leprosy

Correspondence Address:
A B Gupta

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Transepidermal water loss (TEWL), high frequency electrical conductance (HFC) and the hydration state index (HSI) were measured in sldn lesions of 30 paucibacillary leprosy patients and compared with the contralateral uninvolved skin. While the TEWL, HFC and HSI all showed lower values in the lesion site, as compared to the contralateral skin sites, the differences between the two sets of values significant in HFC and. HSI only at 2% and 1% level respectively. A significant positive correlation (r = 0.69) was found to eidst between these two parameters. The parameters correlate well with the known reduced sweating in skin lesions of TT and BT leprosy and may therefore be considered as good objective parameters to confirm hypohydrosis in suspected skin lesions ofleprosy.

Keywords: Transepidermal water loss, electrical conductance, hydration state, leprosy.

How to cite this article:
Gupta A B, Tutakne M A, Haldar B. Measurement of some biophysical parameters in skin lesions of leprosy. Indian J Dermatol Venereol Leprol 1990;56:367-70

How to cite this URL:
Gupta A B, Tutakne M A, Haldar B. Measurement of some biophysical parameters in skin lesions of leprosy. Indian J Dermatol Venereol Leprol [serial online] 1990 [cited 2021 Jan 24];56:367-70. Available from:

Evaluation of sensory perception and sweat response to pilocarpine injection are the two important tests for the diagnosis of paucibacillary leprosy and their importance can hardly be overestimated.[1],[2] However, testing of sensory perception is essentially subjective, being limited by the patient's own understanding. These 'tests cannot therefore be properly performed in infants and young children. Moreover, the pilocarpine injection test is time-consuming and not expressible in measurable units. It was therefore considered useful to study some relevant biophysical parameters that could be measured quantitatively to assess the differences in their values between the affected and the uninvolved contralateral area of paucibacillary leprosy patients. The parameters selected were those that could correlate well with the state of hydration of the skin, namely the transepidermal water loss (TEWL), high frequency electrical conductance (HFC) and the hydration state index (HSI) of the stratum corneum.

  Materials and methods Top

Thirty male patients having paucibacillary leprosy (5 indeterminate, 7 TT and 18 BT) for duration varying from 5 months to 4 years in the age range 22 to 37 years constituted the sample population. For each patient, the parameters were measured at the lesion site and also at the lesion-free, uninvolved identical contralateral site so that the patient himself was his control.

The measuring device for TEWL was Evaporimeter EP 1 of Servomed, Sweden. The technique is based on the estimation of vapour pressure gradient in the air layer immediately adjacent to the skin. If the vapour pressure distribution in this layer is known, the amount of water vapour evaporating per unit time per unit area (TEWL) can be calculated according to the equation

where dp/dx is the vapour pressure gradient in Pascal per metre (Pa/m) in the air layer immediately adjacent to the skin, (dm/ dt)/A is the evaporation rate in g/m2h and D' is a constant (having the value 0.67 x 10-3 g/ mhPa) related to the diffusion constant D.

In the steady state, the evaporation rate is stationary and so the vapour pressure gradient is approximately constant. Consequently, this gradient and hence also the evaporation rate are proportional to the difference between the vapour pressure at two separate points located on a line perpendicular to the evaporative surface. The actual vapour pressure at each point is calculated from the formula

that is the product of relative humanity rh and the saturated vapour pressure Psat The relative humanity is measured with a capacitative sensor based on an organic polymer dielectric sensitive to changes in rh only. The saturated vapour pressure is a function of temperature only and is calculated from the temperature obtained with a fast thermistor at each point of measurement.

The HFC was measured by an instrument called Skicon 200 of IBS Co., Japan. It employs a probe with concentric dry electrodes of gold connected to a tuning circuit. When the probe contacts the skin surface, the conductance between the electrodes, via the skin surface, is detected as resonance voltage change of the tuning circuit. Since very high frequency (3.5 MHz) is employed, dry electrodes could be used.

The output of a 3.5 MHz quartz oscillator is applied to the tuning circuit through a buffer amplifier. When the probe is not in contact with the skin, the tuning circuit resonates and the resonance voltage and reference voltage are equal, and the meter indication is zero. When the probe contacts the skin, the conductance 1/R x (R. = resistance) of the horny layer of skin and the capacitance C, of it are connected to the tuning circuit. The resonance voltage is thereby changed and the device could be calibrated to get the impedance, or for that matter, the conductance of the skin surface.

The hydration state index of skin was measured by Corneometer CM 820 of Courage and Khazaka, Koln, West Germany. It consists essentially of a console housing and a humidity sensing probe. The measured value appears as a maximum three-digit figure on a 40 x 18 mm display. The method is based on the fact that the capacitance of a suitably-shaped measuring capacitor, when brought in contact with varying amounts of water, varies strictly according to the water content. The variations of the capacitance of the probe capacitor is automatically recorded by the device. The display records a value 0-10 when the sensing probe is in contact with dry air and 150-160 with a completely moist pump. Within this range, the different readings would indicate the different degree of hydration.

The experiments were conducted at a mean ambient temperature 24.4 + 1.9° C and a mean humidity 56.8 ± 9.7%.

  Results and comments Top

The results of the investigation are presented in [Table - 1][Table - 2][Table - 3].

It is observed from the tables that all the three parameters show lower values at the lesion site, as compared to those at the uninvolved contralateral ones. On statistical analysis of data by paired t-test, however, it is found that the difference between the two sets of values is significant only in electrical conductance and hydration state index at 2% and 1% level respectively. The difference in respect of TEWL however is not statistically significant (p 0.10). From the -consideration of both HFC and HSI, therefore, it may be concluded that the lesional skin in leprosy is less hydrated than the uninvolved contralateral skin. The observations agree well with the known reduced sweating in skin lesions of TT and BT leprosy due to autonomic nerve damage within the lesions[2]. It is also observed, on analysis, that the two parameters, HFC and HSI are strongly positively correlated (r = 0.69). This however is quite expected. First, they relate to the same individual and secondly, the more the hydration, more would be the electrical conductance.

As regards TEWL, many studies earlier[3] derived moisture content of skin from the transepidermal water loss measurement, assuming that a higher water content of the skin will be manifested by a greater evaporation rate. As a matter of fact, however, TEWL indicates the rate of water movement and not the water content per se. It is a measure of the barrier function of the skin; the more efficient and substantial the barrier, the lower is the TEWL[4]. If TEWL is taken as a measure of skin hydration, the results may appear paradoxical. The markedly elevated TEWL in psoriatic skin would predict a high moisture content when, in fact, they present with dry flaky skin. Conversely, an occlusive film of petrolatum is an efficient moisturiser, but greatly decreases TEWL[5]. The results of the TEWL measurement thus indicate that the barrier function of the skin in paucibacillary leprosy remains essentially unaffected.

In conclusion, the study shows that high frequency electrical conductance, hydration state index and the transepidermal water loss measurements provide good objective and quantitative parameters to confirm hypohidrosis in suspected skin lesions of leprosy.

  References Top

1.Brycesson A and Pfaltzgraff : Leprosy, 2nd ed, Churchill Livingstone, New York, 1979; p 28-35.  Back to cited text no. 1    
2.Hastings RC and Convit J : Leprosy, 1st ed, Churchill Livingstone, New York, 1985; p 146.  Back to cited text no. 2    
3.Rietschel RL : A method to evaluate skin moisturizers in vivo, J Invest Dermatol, 1978; 70 152-155.  Back to cited text no. 3    
4.Tagami H, Kanamaru Y et al : Water sorption­desorption test of the skin in vivo for functional assessment of the stratum corneum, J Invest Dermatol, 1982; 78 : 425-428.  Back to cited text no. 4    
5.Tagami H Yoshikuni K : Interrelationship between water-barrier functions of pathologic stratum corneum, Arch Dermatol, 1985; 121 : 642-645.  Back to cited text no. 5    


[Table - 1], [Table - 2], [Table - 3]


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