RESEARCH REPORT

Lower touch sensibility in the extremities of healthyIndians: further deterioration with age

SumanJain, Syed Muzzafarullah, Sundaresh Peri, Ramesh Ellanti,Krishna Moorthy, and Indira Nath

Clinical & Epidemiology Division, Blue Peter Research Centre, LEPRA Society, Cherlapally, Hyderabad, India

Abstract Touch sensibility testing is a cost-effective, psychophysical measure ofperipheral nerve function and impairment. However, there is limited information regardingthe natural variability in touch sensibility across different populations and different agegroups. We studied 568 healthy Indian volunteers without any clinical evidence of peri-pheral nerve disease. Touch sensibility was evaluated bilaterally in palms, feet, and heels,using Semmes-Weinstein monofilaments, with target forces ranging from 0.008 to 300 g.No differences were observed between the right and the left limbs. The lowest targetforce detected ranged from 0.4 to 2 g in the palms and 1.4 to 15 g in the feet. These val-ues showed further increase with age. Women compared with men had higher sensibilityin the palms in most age groups. Touch sensibility thresholds recorded in a large group ofIndians were higher than that reported in other populations. These findings have clinicalimplications for the diagnosis of early nerve impairment in the elderly and in disease statesdrawing attention to geographic variations in touch sensation.

Key words: aging, neuropathy screening, peripheral nerves, touch sensibility

IntroductionMorbidity and disability are commonly associated

with peripheral nerve impairment in several diseases(Poncelet, 1998; Jaquet et al., 2001; Buhroo, 2003;Jerosch-Herold, 2005; Wampler et al., 2005). Bothmuscle testing and sensory impairment have beencommonly used to assess such nerve deficits. Clini-cally, sensory function is more easily assessed bymeasures of perceptual threshold than by electro-physiology. Sensory testing has suffered from lack ofconsensus on the methodologies to be used as wellas lack of standardized protocols for comparison

between different populations and centers. Such val-ues are required for assessing sensory impairmentand for evaluating improvements following therapeu-tic interventions and sensory re-education.

Semmes-Weinstein nylon monofilaments (SWM)provide a practical, acceptable, reproducible, and cost-effective methodology for use in the clinic and thefield to measure cutaneous pressure thresholds(Bell-Krotoski and Tomancik, 1987; Bell-Krotoski et al.,1995; Anderson and Croft, 1999). SWM primarily dis-criminates light touch and deep pressure sensations.Most studies using SWM filaments show differingthresholds making it difficult to evaluate the naturalvariations across populations (Malaviya et al., 1994;Kets et al., 1996; Birke et al., 2000; Jeng et al., 2000;McPoil and Cornwall, 2006). We used the full set ofSWM to study both palms and feet in a large numberof healthy subjects (10–80 years) with a similar socio-economic background in India.

Address correspondence to: Dr. Indira Nath MD, FRCPath, DSc(hc),Blue Peter Research Centre, LEPRA Society, Cherlapally, Hyderabad501301, India. Tel: þ91 40 27264547; Fax: þ91 40 27261262; E-mail:indiranath@gmail.com; indiranath@bprcleprasociety.org

Journal of the Peripheral Nervous System 13:47–53 (2008)

ª 2008 Peripheral Nerve Society 47 Blackwell Publishing

Material and MethodsSubjects

Five hundred sixty-eight volunteers (282 femalesand 286 males) aged 10–80 years, residing in Hydera-bad, India, were enrolled for the study after excludingneuropathy based on history and clinical examination.Three females and two males were 80 years of age.Subjects were from a similar socioeconomic group andwere not employed in manual labor. All subjects werephysically active, wore footwear for outdoor activities,and generally walked barefoot at home and in religiousplaces. They had no history of significant injury or previ-ous surgery in foot, ankle, or hand. Subjects withknown cause of neuropathy or other illnesses thatwould affect study results were excluded. The studyhad the approval of the Institutional Ethics Committee.

Semmes-Weinstein monofilaments

Light touch sensibility was assessed by using afull set of 20 monofilaments of equal length (38 mm),NC12775-01 to NC12775-20 with target forces ran-ging from 0.008 to 300 g obtained from North CoastMedical Inc., San Jose, California.

Testing procedure

Subjects were tested by the same operator toavoid interoperator variations. Prior to testing, the sub-jects were placed in a chair in a quiet room, made com-fortable with a pillow, and counseled about themethodology while they were observing the proce-dure. During testing, they kept their eyes closed toavoid a visual influence. The SWM filaments weretested on palms (six sites) and feet (eight sites) startingfrom the right to the left side, using the staircasemethod (Conomy and Barnes, 1976; Hunter et al.,2005). A series of monofilaments in decreasing orderwere applied starting with the highest SWM of 300 gtarget force until the approximate threshold was deter-mined. Then, a minimum of five monofilaments wereselected where at least two filaments were consecu-tively of higher or lower forces than the approximatelydetermined one. These were used sequentially in threecycles of ascending and descending order. A finalthreshold was recorded as the lowest target forceconsistently detected in three threshold crossings.Periodically, the subjects were rested for 5 min andneighboring sites at distances of 2–5 mm tested toavoid over stimulation of the same sites. To preventfalse positives, subjects were also given mock ex-ercises, without the probe touching the skin.

Data analysis

The data on 15,903 sites on the palms, feet, andheels from 568 subjects were analyzed using analysis

of variance (ANOVA) and nonparametric Kruskal-Wallis with SPSS statistical software. For the purposeof analysis, the subjects were stratified into sevenage groups of one decade each. The data were com-pared between age groups and gender.

ResultsFive hundred sixty-eight healthy subjects from

south India (282 females and 286 males), between10–80 years, were divided into seven age groups(Table 1). Fig. 1 shows the sites tested by SWM. Ingeneral, each of the six sites in a given palm andseven sites in feet had identical values (data notshown). No differences were observed in the contra-lateral sides at any of the matched sites in the palms(p . 0.95) and feet and heels (p . 0.505). Greater var-iability was apparent between the left and the rightsides in the feet and heels compared with the palms,but this was not significant (p . 0.505).

Fig. 2 shows the overall sensory threshold map ofthe total numbers of 15,903 sites tested in theextremities. These show that there is minimal overlapof the touch sensibility between the palms and thefeet/heels. The sites in the palm showed lower thres-hold range compared with the feet. In the palm, 88%of the sites had threshold range of 0.02–0.4 g with61% falling between 0.16 and 0.4 g. Eighty-nine per-cent of the sites in the feet ranged from 0.6 to 1.4 gwith the majority (73%) clustering around 0.6 and 1 g.Interestingly, five subjects with no clinical neuropathyshowed the highest touch threshold of 15 g. Though91% of the sites in the heels ranged from 0.6 to 2 g,the threshold peak (71%) was at the 2 g target force.In general, the palms showed the highest and theheels the lowest sensory perception with the feetshowing intermediate values (p , 0.0001 ANOVA andKruskal-Wallis).

Table 1. Gender distribution among the seven age groups of568 healthy subjects tested for touch sensibility in palms, feet,and heels.

Age groups (years)

Number of subjects

TotalFemale Male

10^19 45 45 9020^29 46 49 9530^39 51 50 10140^49 54 45 9950^59 50 57 10760^69 14 20 3470^80 22 20 42Total 282 286 568

Jain et al. Journal of the Peripheral Nervous System 13:47–53 (2008)

48

Age-related reduction in sensory perception

The palms showed a marked age-related touchthreshold increase commensurate with decreased sen-sory perception from second to sixth decade (Table 2;p , 0.0001) with a significant but less marked increasefrom seventh to eighth decade (p , 0.0001). The feetalso showed comparable highly significant age-relatedincrease in touch threshold (p , 0.0001), even thoughthe mean � SD and 95% CI differences were lessmarked in the earlier decades and more evident in thepast two decades. Moreover, the 99th percentile ofthe two oldest age groups showed a mean target forceof 15 g. A similar increase in touch threshold withadvancing age was also observed in the heels.

Relationship of gender and sensory perception

Gender taken alone did not show a relationshipwith touch sensibility thresholds. However, there isan interactive effect of age and gender. Table 3shows that the palms of females had lower touchsensibility thresholds compared with the males in allthe age groups (p , 0.0001), except for fifth andeighth decades. In the lower extremities, significantgender-based differences were also observed insome age groups (p , 0.01 to , 0.05).

DiscussionMonofilament nylons are being increasingly used

for screening and monitoring of peripheral nerve func-tion, in part due to low cost (Imai et al., 1989; Kumaret al., 1991; Sosenko et al., 1999; Olaleye et al., 2001;Lee et al., 2003; Meek et al., 2003; Pratorius et al.,2003; Frykberg et al., 2006; Modawal et al., 2006;

Wilgis et al., 2006; Melchior et al., 2007). Such psy-chophysical testing methods are useful because theyprovide an overall assessment of sensation and im-pairment (Dyck et al., 1993). Semmes and Weinsteindefined the original level of normal touch thresholdon subjects in the United States (Weinstein, 1993;Boscheinen-Morrin and Conolly, 2001). The upperlimit for touch sensation for palms and soles was re-ported as 0.068 and 0.2 g target force (Kets et al.,1996). Studies conducted in Nepal (Kets et al., 1996),north India (Malaviya et al., 1994), and Thailand (Birkeet al., 2000) on 136, 57, and 112 normal subjects,respectively, showed far higher values of 0.2–0.6 gfor palms and 2 g for feet. Except in one study on thefoot (McPoil and Cornwall, 2006), the role of genderhad not been reported (Malaviya et al., 1994; Ketset al., 1996; Birke et al., 2000). These variationsprompted us to investigate the normal range of sensi-bility thresholds in a larger group of healthy Indian in-dividuals of both sexes who were not exposed tomanual labor.

Importantly, the sensory detection threshold inthe extremities of healthy Indian subjects is muchhigher than reported for the Western populations(Jeng et al., 2000; McPoil and Cornwall, 2006). Thisincrease is evident in both sexes and across the ageof 10–80 years. Touch threshold values in our studyare closer to reports from Asia where only a partialset of SWM filaments were used (Malaviya et al.,1994; Kets et al., 1996; Birke et al., 2000; Mitchell andMitchell, 2000).

As expected, the touch threshold levels of eachof the ipsilateral sites of both limbs were identical fora given subject, indicating uniformity of sensory fibersupply and receptor density. Overall, the sensibilitythresholds of the palms showed minimal overlap with

Figure 1. Location of tested sites on extremities. Sites on the palms, dorsum, and plantar surfaces of feet tested for touchsensibility using Semmes-Weinstein monofilaments. Numbers refer to the site tested and are the same as given in tables.Peripheral nerve trunks enervating the sites are indicated by arrows. The vertical line in the palm distinguishes areas enervatedby ulnar and median nerves.

Jain et al. Journal of the Peripheral Nervous System 13:47–53 (2008)

49

the feet and the heels. In agreement with other stud-ies (Malaviya et al., 1994; Kets et al., 1996; Birkeet al., 2000), the sensibility threshold level was signifi-cantly lower in the palms compared with the feet inthe same subject as well as in the group as a whole.

The higher tactile threshold seen in the feet comparedwith the palm may also be due to the thicker layer ofkeratin seen in plantar skin (Malaviya et al., 1994; Ketset al., 1996; McPoil and Cornwall, 2006) or due to eth-nic factors and cultural habits of walking barefoot. The

Figure 2. Touch thresholds in palms showing minimal overlap with feet and heels. A total of 15,903 sites from right and leftextremities of 568 healthy subjects were tested as in Fig. 1. Data are normalized as percentage (%) of sites (y-axis), whichresponded to a given target force (x-axis). Numbers in parentheses give number of sites tested for each category. Numbersabove bars indicate clustering of sites (%) for the given target forces. Highest target force of 15 g was detected in 40 sites offeet/heel. The p value by analysis of variance and Kruskal-Wallis for palm vs. foot vs. heel is p , 0.0001.

Jain et al. Journal of the Peripheral Nervous System 13:47–53 (2008)

50

Table

3.Gen

derd

ifferen

cesstratifiedby

agegroup

sintouc

hthresholdvalues

inthepalms,feet,and

heelsof2

82femalean

d286malehealth

ysubjects.

Age

group

s(years)

Meantarget

force(g)�SD(95%CI)

Palms

Feet

Heels

Fem

ale

Male

Fem

ale

Male

Female

Male

10^19

0.03�0.06*(0.02^0

.03)

0.03�0.03*(0.03^0

.04)

0.80�0.41

**(0.76^0

.83)

0.80�0.23**

(0.73^0

.80)

0.80�0.40(0.71^0

.88)

0.80�0.20(0.71^0

.88)

20^2

90.08�0.09*(0.07^0

.09)

0.13

�0.10

*(0.12^0

.13)

0.80�0.30(0.75^0

.80)

0.80�0.22(0.76^0

.80)

1.80�0.5(1.70^1.90)

1.70

�0.50(1.50^1.70)

30^3

90.21

�0.14

*(0.20^0

.22)

0.17

�0.12

*(0.16^0

.18)

1.10

�0.51

(1.10^1.13)

1.10

�0.51

(1.10^1.13)

2.30�1.20#(2.04^2

.52)

2.00�0.30#(1.90^2

.00)

40^4

90.25�0.14

(0.23^0

.25)

0.23�0.14

(0.21^0

.24)

1.00�0.30*(1.00^1.10)

1.10

�0.30*(1.10^1.12)

2.10�0.90#(1.90^2

.20)

1.90�0.40#(1.70^1.90)

50^5

90.27�0.12

*(0.26^0

.28)

0.34�0.26*(0.31^0

.35)

1.10

�0.30#(1.10^1.13)

1.20�0.50#(1.13^1.20)

2.00�0.10

#(1.97^2

.01)

2.00�0.30(1.90^2

.08)

60^6

90.29�0.15

*(0.26^0

.30)

0.35�0.18

*(0.32^0

.37)

1.30�0.47

#(1.20^1.40)

2.30�3.27(1.90^2

.70)

2.00�0.20#(1.80^2

.01)

3.00�3.10

#(1.90^3

.90)

70^8

00.31

�0.28(0.27^0

.33)

0.31

�0.27(0.27^0

.34)

4.90�4.20#(4.40^5

.30)

4.20�2.90#(3.80^4

.50)

5.10�4.00(3.80^6

.20)

4.40�2.70(3.50^5

.20)

Allag

es0.19

�0.17*(0.18^0

.20)

0.21

�0.20*(0.20^0

.21)

1.29�1.60(1.24^1.30)

1.30�1.49(1.25^1.30)

2.08�1.64(1.94^2

.21)

1.98�1.42(1.90^2

.10)

*p,0.0001;**p,0.01;

#p,0.05:fem

alevs.m

aleby

analysisofvarianc

ean

dKruskal-W

allis.

Table

2.Age

-related

increase

intouc

hthresholdvalues

inthepalms,feet,and

heelsof5

68health

ysubjectsexpressed

astarget

force(g)de

tected

byresp

onse

toSem

mes-

Weins

teinmon

ofilam

ents.*

Age

group

s(years)

Meantarget

force(g)�SD(95%CI)

Palms

Feet

Heels

10^19

0.03�0.05(0.03^0

.04)

0.77�0.33(0.75^0

.79)

0.77�0.33(0.72^0

.82)

20^2

90.01�0.10

(0.10^0

.11)

0.78

�0.25(0.76^0

.79)

1.76

�0.51

(1.68^1.83)

30^3

90.19

�0.13

(0.19^0

.20)

1.10

�0.51

(1.07^1.13)

2.15�0.91

(2.02^2

.22)

40^4

90.24�0.14

(0.23^0

.25)

1.07

�0.29(1.05^1.09)

1.99�0.72

(1.88^2

.09)

50^5

90.31

�0.21

(0.29^0

.32)

1.14

�0.41

(1.12^1.16)

2.01�0.21

(1.98^2

.09)

60^6

90.32�0.17

(0.31^0

.34)

1.91

�2.58(1.67^2

.14)

2.54�2.42(1.95^3

.13)

70^8

00.32�0.27(0.28^0

.33)

4.52�3.63(4.23^4

.81)

4.76

�3.46(4.00^5

.50)

Allag

es0.20�0.18

(0.19^0

.20)

1.30�1.54(1.27^1.33)

2.02�1.53(1.94^2

.11)

*p,0.0001:palmsvs.feetvs.heelsby

analysisofvarianc

ean

dKruskal-W

allis.

Jain et al. Journal of the Peripheral Nervous System 13:47–53 (2008)

51

plantar surfaces showed more variations than thepalms at individual sites, but this was not significant.We also found that the heel area showed the greatestintersite variation and was the least sensitive, perhapsdue to its load-bearing functions (Thomas et al., 2003;Rosenbaum et al., 2006).

As in other reports (Horch et al., 1992; Malaviyaet al., 1994; Kets et al., 1996; Birke et al., 2000;Mitchell and Mitchell, 2000; Verdu et al., 2000;Tremblay et al., 2005; McPoil and Cornwall, 2006;Modawal et al., 2006; Perry, 2006), our observationsshowed a strong correlation of sensory perceptionlevel with age. A sequential and significant sensoryloss was observable with increasing age in both thefeet and the palms. Importantly, in our study, thehighest threshold in the plantar surface in the olderage is 15 g. This is higher than in other studies where10 g was considered to define loss of sensationobserved in diabetic patients (Armstrong et al., 1998;Lee et al., 2003; Mayfield and Sugarman, 2001). In-dians in general not only appear to have a decrease intouch sensibility to those from the developed nationsbut also show an increased deterioration with aging.

Gender taken alone did not show a relationshipwith the level of sensory perception. Of interest is ourobservation that gender contributed significantlywhen the subjects were stratified on the basis of age.Paradoxically, the plantar surface of men appeared tobe more sensitive than women in general. Whetherthis was due to greater access of men to footwearcompared with women could not be confirmed defini-tively. Our study indicates that natural variabilities indifferent populations need to be considered whileevaluating early loss/reduced sensory perception indisease states.

AcknowledgementsWe thank the Zilla Parishad High Schools of Ram-

pally and Zilla Parishad Secondary School, Cherlapally,Hyderabad, India, for providing space to test subjects;Ms. T. Anuradha, Prameela Chauhan, and Mr. K. RamanaBabu for recruiting volunteers; Mr. Robert Jerskey forproviding the SMW kit; and Dr. Vijayalakshmi for criti-cal inputs on the manuscript. The study was fundedby the British Leprosy Relief Association, Colchester,UK. Contribution of authors: S.J. is a ResearchMedical Officer who instituted and supervised thestudy. S.M. is the physiotherapist who conducted thesensibility testing. S.P. and R.E. assisted in statisticalanalysis and K.M. assisted in clinical evaluation. I.N.evaluated the results, analysis, and prepared themanuscript.

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