To the Editor,
The article by Saltzman et.al.(1),argues for a redefinition of the cut
off levels of monofilament nylon sensory thresholds in the diabetic foot. We have
reported similar observations in patients with leprosy
wherein we defined the levels of protective sensation as double
the normal sensory thresholds ( 4.7 gms compared to a normal
threshold of 2.35 gms. as revealed by 20 filament set supplied by North
coast medical and Inc. California USA). (2)
We tested 3 sites in each foot of 57 normal controls: first
metatarsal head: fifth metatarsal head: and center of heel.
These areas are innervated by three branches of the posterior tibial
nerve which can be affected in different combinations in leprosy.
We also examined 40 patients with leprosy who had sensory impairments of varying degrees with and
without ulcers. We concluded that all patients who did
not have normal sensation were at risk to develop ulcers. Also, if their
thresholds were double the normal value, the risk increased many fold. (3)
I agree with the authors that there can be "over detection" and the un-necessary
inclusion of some patients in the ulcer risk group. However, this may prove beneficial to these patients because health education and proper self-care practices
will be imparted to them.
The authors have correctly observed that Birke and
Sims made their observations (4) with only 3 nylons and 4.5 gms. Ten grams
makes a big difference. Hammond and Klenerman (5) using a 20 nylon set noted
these levels to be 11.8 gms., but several of their patients had foot
ulcers.
The first metatarsal area of the sole
has been found to have lower thresholds than other areas of foot. In
diabetic neuropathy, presumed to be uniformly diffuse, sensory testing at one site might be
"adequate" but we prefer testing at three sites until it is established with
certainty that selective involvement of branches of posterior tibial nerve
does not occur.
References:
1. Saltzman CL, Rashid R, Hayes A, Fellner C, Fitzpatrick D, Klapach
A, Frantz R and Hillis SL. 4.5 Gram monofilament sensation beneath both
first metatarsal heads indicates protective foot sensation in diabetic
patients. J Bone Joint Surg. 86-A: 717-723,2004
2.Malaviya GN, Husain S, Girdhar A, Girdhar BK. Sensory functions in
limbs of normal persons and leprosy patients with peripheral trunk damage.
Indian J Leprosy 66: 157-164,1994.
3. Malaviya GN, Husain S, Mishra B, Girdhar A, Girdhar BK. Protective
Sensibility - Its monofilament threshold equivalents in leprosy patients.
Indian J Leprosy 69: 149-158,1997.
4. Birke JA and Sims DS. Plantar sensory threshold in the ulcerative
foot. Lepr. Rev. 57:261-267,1986.
5. Hammond CJ and Klenerman P. Protective sensation in the foot in
leprosy. Lepr. Rev. 59:347-354,1988.
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