Age and gender differences in skin sensory threshold assessed by current perception in community-dwelling Japanese.

The purpose of this study was to investigate age and gender differences in current perception thresholds (CPT) in Japanese citizens. CPT values at frequencies of 2000, 250 and 5 Hz reflect different types of peripheral sensory nerve functions. Since there have been only a limited number of reports which investigated CPT values in community-dwelling people, little is known about variations with age and gender. The present study therefore concentrated on a large population of 1632 individuals (men; 818 mean age +/- standard deviation 59.4 +/- 10.9, women; 814, 59.4 +/- 11.1) in a Japanese community. Significant gender differences in CPT values at 250 and 5 Hz were observed. Multiple comparisons among 4 age groups (40s, 50s, 60s and 70s) showed age-related differences in CPT values at 2000 and 250 Hz in both genders. However, age and gender interactions with reference to CPT values appeared to be different between these latter two frequencies. At 5 Hz, only men showed age-related variations. These results indicated gender differences in fiber-specific aging changes.

There have been many clinical investigations into diabetic neuropathy 7-10 ), carpal tunnel syndrome 11,12 ) and other peripheral neuropathy 13) with the Neurometer. The results indicated its potential advantages for epidemiological studies of peripheral neuropathy.
However, little is known about age and gender effects on CPT values because there have only been a limited number of epidemiological studies on community-living people. The effects of aging 14) or gender 15 ) on CPT values were investigated in only small populations with less than 200 subjects. In the present case, we examined age and gender differences in CPT values obtained from a relatively large community-dwelling population.    CPT at these higher frequencies.

MATERIALS AND METHODS
As shown in Table 5, a significant gender difference in CPT values at 5Hz in middle-aged people was found. No previous studies detected such age and gender interaction at this frequency. Presumably, the results reflect the large number of participants in our study and the associated high statistical power. At this frequency, the Neurometer stimulates C fibers selectively, conveying noxious stimuli 17). The electrically stimulated pain threshold is known to be similar to that of clinical pain due to activation of C fibers 19). Thus, CPT values at 5 Hz may have relevance to the pain threshold due to electrical stimulation. In fact, CPT stimulus at 5 Hz is sensed as 'burning' or 'stinging' and is unpleasant at increased stimulus levels . On the other hand, stimulus at 2000 Hz is sensed as 'buzzing' or 'tingling' without unpleasant pain at increased stimulus 5). Gender differences in the pain threshold, especially the electrical stimulation pain threshold are well known 20). With electrical pain stimulation, women show a significantly lower electrical pain threshold than men 20). This biological mechanism is considered to depend on central processing for noxious stimuli 21). Significant variations at 5 Hz between men and women in the 40s and 50s groups in our study may be related to this.
Our results also showed age-related changes in CPT values at 5 Hz were only seen in men. Taking into account the fact that unmyelinated fibers are thought to be hardly affected by aging 16), the age-related change at 5 Hz in men may be a consequence of aging changes in the central processing system for noxious stimuli, rather than in peripheral sensory nerve fibers themselves. The lack of gender differences in CPT values at 5 Hz in the 60s and 70s groups is consistent with this hypothesis.
Our study had some limitations. For example, a detailed neurological examination was not performed. Patients with peripheral neuropathies are reported to show significantly higher CPT values compared with normal subjects 15,17) It is probable that age and gender interaction on CPT values obtained from our subjects, who were confirmed to be normal by detailed neurological examination, may be different from our results. A second limitation is the limited period of training for CPT testing. In the NILS-LSA, evaluations for participants are scheduled in a relatively busy time schedule. Thus, participants must take CPT testing without sufficient knowledge of the sensation of this current.
The present results indicated the important effects of age and gender on CPT values at different frequencies in clinical or epidemiological studies. CPT testing appears to have strong potential to provide useful information in epidemiological or clinical studies because of its comparability and reproducibility. Recently, new CPT application techniques for the determination of neuroselective electrical pain perception thresholds have been used 22). Studies have been conducted on the effects of narcotics 23) and local analgesics 4) with this new application. Our results indicated significant age and gender interaction in CPT values at 5 Hz, which is associated with pain thresholds.
In epidemiological or clinical studies with the Neurometer, especially with such new applications, age and gender differences should be considered when interpreting results.