The threshold for protective sensation that prevents neuropathic ulceration on the plantar aspect of the foot: a study of leprosy patients in a rural community in India.

The protective sensation threshold is an important concept in the prevention of plantar ulceration in leprosy patients. Previous studies have suggested that skin with sensory nerve damage on the plantar aspect of the foot which can still detect the 5.07 Semmes-Weinstein monofilament (approximately 10 g) is highly unlikely to develop ulceration. While the threshold is thought to be less than the 610 filament (approximately 75 g), no work just testing adjacent to current ulcers has been undertaken to assess this more accurately. This is important, as it has been shown that a significant proportion of healthy individuals who wear sandals or go barefoot in India may fail to detect this 5.07 filament in at least some areas of the sole, especially in older age groups, and in certain cases the 5.46 filament (approximately 30 g) is the lightest detected. In an attempt to address this problem, a cross-sectional study on 26 current plantar ulcers in male adults with stable neuropathy due to leprosy was carried out in the rural town of Salur, India. It was confirmed that the ability to detect the 5.07 filament (approximately 10 g) did prevent the development of ulceration while in contrast the ability to detect the 5.46 filament (approximately 30 g) did not. This suggests that the threshold for protective sensation lies between these two filaments. An approach is suggested which may help to differentiate feet genuinely at risk of ulceration from those merely unable to detect the 5.07 filament on account of thickened skin callus or advancing age.