NEUROPATHIC FOOT IN LEPROSY - METHODS OF ASSESSMENT

DEFINITION:

“Neuropathic foot is defined as a foot in which there is loss of function of at least one of the three modalities of peripheral nerve function: motor, sensory and autonomic nerve function”.

- W R Faber, 2003

Introduction:

Neuropathy is common in patients with leprosy and is considered to be one of the primary risk factors for plantar ulceration. Problems associated with leprous neuropathy include loss of pain sensation, which predisposes the foot to unnoticed trauma, neuropathic deformities and autonomic problems. In addition, the leprosy patients may have other concomitant neurological conditions so a thorough neurological examination is indicated at the initial consultation with reviews concentrating on areas which are known or suspected to be problematic. Several studies have shown that in leprosy the frequency of foot deformities is more than hand deformities.This is probably due to the difficulty in recognizing the foot problems at an early stage and identifies the factors that cause damage to the foot. It is worth recording the deformity status of the foot that would help to evolve new parameters and their possible application in assessment of leprosy control programme.

Materials & methods:

We reviewed various assessment methods described by several authors published in the literature, mostly from leprosy journals reported by several authors and summarized the findings. It is imperative to mention that most studies on this subject do not have unanimity of opinion and they are largely confined to endemic countries.In this presentation, we are outlining the details of the methods of assessing the foot as well as its effect in identifying the underlying foot problems, which can serve as a guide to those interested in treating the foot problems due to leprosy.We have classified this review into various sub-headings like history, physical examination, sensory assessment, temperature and pressure measurement, autonomic function and voluntary muscle testing (manual muscle strength testing).   

A. History:

A thorough history and examination of each of these areas will provide the clinician with a good understanding of the patient's foot problems and this information will assist in formulating a treatment plan or prophylactic and educational measures, which may need to be undertaken. It is important to record the personal details of the patients such as name, age, sex, address, occupation, place of work, distance from house, type of work [sedentary or heavy, standing & walking hours], present complaints [foot injury (recurrent), Inability to walk properly (High-step gait) & loss of sensation over sole], history of injury [usually noticed only after insult to skin-plantar ulcers, knife / glass cut], disease [Diabetes, Kochs], habits [smoking/alcohol/hygiene] and family history [married / unmarried / non-dependent].  These may be useful in formulating preventive measures in order to integrate social with medical measures.

B. Physical examination:

Physical examination of patients tended to consist mainly of qualitative techniques, which did not require the use of equipment. The following factors are helpful in detecting the pre-ulcerative stages and this should form as a part of routine clinical examination of the patient suffering from leprosy.

5                   Skin [dry, scaly, callosities (with / without ulcers)],

5                   Attitude [Usually plantar-flexed compared to normal limb due to paralysis of tendo-achilles (predisposing to more injury)],

5                   Deformity [Hallux valgus (Abductor Hallucis), Clawing of toes (Intrinsic muscles), Flattening of arch of foot (Weakness of short flexors)],

5                   Swelling, Redness, Muscle wasting

5                   Joint [Ankle Joint (Tenderness, swelling) and toes (stiffness & deviation)]

5                   Palpation of nerve [Lateral Popliteal Nerve (Head of fibula) & Posterior Tibial Nerve (behind medial malleoli)] to know whether it is tender or thickened like a cord. Tenderness of Posterior Tibial Nerve due to inflamed lymphatics is common among the leprosy patients who completed multi-drug therapy and having infected planter ulcers (Anil Patki, 1993),

                                                                       

C Sensory assessment:

Historically, neuropathy was assessed on signs and symptoms alone. Maser et al consider that "clinical assessment of neuropathy lacks precision and reliability, is semiquantitative at best, and often leaves subtle forms of nerve dysfunction undetected". The issue of reliability in any standard assessment method is of importance. Quantitative sensory testing with various types of equipment has become accepted practice in recent years, and some common techniques are described below.

1. TACTILE

1.1. Ball-point pen / pencil

In 1970, WHO Expert Committee on leprosy stated that “the failure to localize firm touch with the tip of a ball-point pen is a useful sign that patient is now in danger from mechanical injury & burns”. Stratford et al had also stated that “there is loss of protective sensation when patient can’t localize a firm touch with the tip of a ball-point pen and is liable to suffer frequent injury”.The testing is done with the patient blindfolded and exert pressure just enough to dimple the skin (not to move feet / toes) using the point of ball-point pen or tip of a pencil.If the patient recognizes accurately with in 2cm in all sites the result is positive and inability to recognize in 1 or more sites is considered as negative.The advantages are its wide availability and cheap.However the disadvantages are its difficulty to exert standard pressure and high probability of under diagnosing sensory loss as observed by LF Koelewijn (2003).

1.2. Semmes Weinstein Monofilaments

SW nylon monofilaments are advocated since1970’s in the filed of leprosy.These nylon filaments are buckled at a reproducible stress and may be identified by the manufacturers’ numbers ranging from 1.65 to 6.65 [common logarithm of ten times the monofilaments buckling force in milligrams] as measured by Birke (1986).The length of the nylon filament should be 38 mm as described by LF Koelewijn (2003).The testing method has been standardized and should be carried out in a quiet area.The nylon filament is mounted on a handle and is applied perpendicular at the pre-identified site and holds it till the filament form “C” position. The following table shows the pressure of monofilaments (in gms) used in various studies by different authors.

Force	Authors
0.5 gms	CJ Stratford et al (1994)
1 gms	JA Birke et al (1986)
2 gms	CJ Stratford et al (1994); LF Koelewijn(2003)
5 gms	CJ Stratford et al (1994)
10 gms	J A Birke et al (1986); Dorairaj et al (1988); CJ Stratford et al (1994); LF Koelewijn(2003)
50 gms	LF Koelewijn(2003)
75 gms	JA Birke et al (1986) ; Dorairaj et al (1988)
300 gms	Dorairaj et al (1988) ; LF koelewijn(2003)

          

Judith Bell-krotoski (1990) had used a set of 5 SW nylon filaments and the specifications are as follows:             

Manufactures No.	Force in gms	Color
2.83	0.06	Green
3.61	0.4	Blue
4.31	2	Purple
4.56	3.6	Red
6.65	447	Orange

Birke et al (1986) had tested 132 plantar ulcer sites in 72 Leprosy patients and concluded that the lowest pressure threshold among those patients with plantar ulcers is SW filament 6.10 and the level of protective sensation among those who use footwear is SW filament 5.07.They also said that barefoot walking results in hypertrophy of the plantar soft tissues and may alter the threshold of pressure sensation.The advantages with the graded monofilaments are its accuracy and reproducibility.The disadvantages are that the nylon filament is not easily available and mounted filaments are expensive.The other practical problems are the filaments may be lost and the force is likely to change with temperature and frequent usage.But local production of handle and filaments (local calibration) as shown by Dorairaj et al of Karigiri, TN (1988) is possible. Van Brakel (1994) had used a set of 6 coloured monofilaments fitted in custom-made handles of refrigerator wire, but concluded that there is a need to standardize the number of filaments, its length, thickness, mounting pressure and the application procedure. He also warned a high degree of inter-observer variation if the test is carried out with the health workers who are not trained properly.

2. VIBRATION SENSE

2.1. Tuning Fork

A supramaximal stimulus is applied using tuning fork by applying the prongs on volar / plantar surface of each distal phalanx. Prongs were held over until patient no longer feels (vibration, electrical or similar). Normally the patient recognizes the vibratory sense equal at the proximal & distal sites. Various frequencies have been used by different authors and they are 120 hz [CJ Stratford (1994)], 128 hz [JAHSS; Van Brakel (1994)] and 256 hz [J A Birke (1986)].

2.2. Biothesiometer (C J Stratford, 1994)

It is a battery operated instrument with a fixed frequency of 120 hz and with amplitude ranging from 0 – 25 micro meter.It has a probe to be held lightly on the testing site.The amplitude of vibration is recorded and repeated for 3 times and the mean is calculated. They included 72 leprosy patients (with \ without ulcers) (36 controls & 36 study) in the trial and further classified them into those wearing or not wearing shoes. It was found that the sensitivity levels were ranging from 70 to 100% and specificity levels were ranging from 83 to 100%. The disadvantage of this method is the high prohibitive cost ($400). Studies recommend that the normal frequency is ranging from 120 / 128 hz.

D. TEMPERATURE

1. Hot & cold test tube

Entire surface of foot and ankle is scanned using test tubes containing hot and cold water and compare with normal part.The difference in temperature is noted.This test is simple and can be performed easily, however the disadvantage is its inaccuracy (<2*C) and subject to change in normal humidity.

2. Infrared Thermometer as thermocouple

It consists of a probe indicating temperature which is measured by placing the probe on the skin.This instrument is small, durable, less expensive (less than $ 200) and accurate (0.1* C).The disadvantages are its slow response (10-20s) and poor screening capabilities.

3. Thermograms              

This equipment measures the thermal (IR) emission of energy from an object and projects it in a manner similar to a television images on video screen. The warm areas are shown in shades of white and cooler areas are shown in darker shades.A single temperature may be electronically highlighted as bright light.The use of two such isotherms allows the operator to measure absolute temperature and difference between highlighted areas.The advantages are its ability for rapid screening, its accuracy (0.2*C) and non-contact method.The disadvantage is it is very expensive - $30,000.

E. DOT DISCRIMINATION

4.1. Static 2 – Point Discrimination

This is tested using the two points of a ‘divider’ (available in geometry box) or heads of 2 pins placed simultaneously.Distance is then reduced between two points till it gives sensation of single point. This is used to test the innervation density of skin.

4.2. Moving 2 – Point Discrimination

A circular plastic disk on which pairs of metal prongs are mounted with different inter-prong distance is used. Explain the method to patient. Randomly the prongs are moved from proximal to distal over the site with a distance (1.5-2cm) applying little pressure. Patient was asked whether he felt 1 or 2 prongs. Paperclip can also be used.

F. PAIN SENSATION

Pain sensation is tested using standardized wooden toothpicks.The toothpick was applied randomly with the sharp end or the blunt end and the patient was asked to say whether he felt ‘sharp’ or ‘blunt’.Devices with spring loaded or sliding weights have been used by Jain et al (1986).

G. JOINT POSITION SENSE

The middle phalanx is fixed between thumb and index finger of the examiner. The examiner gently moves the distal phalanx either up or down from the neutral position. The patient is then asked to say whether he felt his finger or toe moving up or down.

H. PRESSURE SENSE

1. Barograph (Patil, 1986)

This instrument measures pressure distribution under normal and leprotic feet using a barograph. The barograph consists of a glass plate illuminated at its edges by fluorescent lights. The top surface of the glass plate is covered by a thin sheet of opaque white plastic upon which the subject stands. Greater pressure levels cause more intimate contact between the plastic and the glass, which results in the breakdown of total internal reflections within the glass. When viewed from a 45 degree inclined mirror placed below the glass plate, the areas of contact of the foot can be seen with light intensity related to the applied pressure. The resulting image recorded photographically is scanned for pressure intensity patterns using a microdensitometer. The pressure intensities are calibrated using known weights over specified areas.

2. Harris mat

It consists of a flexible rubber mat with small porous of equal size. Ink is spread over the mat and a paper is then placed while the subject is asked to stand on it.The places with dark ink shades are points of increased pressure. Harris footprints of a patient striding barefoot (A) on a hard floor, (B) on thin soft insole material and (C) on thick soft insole material.

3. F-SCAN System

It consists of an insole pressure sensor and a cuff unit. It gives 3-D Fscan recording in numerical mapping where peak pressure at a particular point can be noted.

I. AUTONOMIC FUNCTION

1. Sweat function test (PK Oommen, 1996)

Sweat prints of the feet are tested using No.1 Whatman filter paper treated with ninhyin and the intensities of the ninhyin positive areas are noted.

2. Arteriographic pattern (B P Debi, 1980)

The arteriographic pattern was tested using Conray-240 as a contrast media. 10 ms of dye was injected into femoral artery using seldingers arterial needle and pressure injector. Needle was removed and the puncture closes automatically. Arteriograms were scanned for caliber course and contour of vessels. 60 arteriograms were studies in 20 cases with 35 planter ulcers (6 months – 2 years). Of which 70% of cases shown tortuous vessel; 50% of cases had narrowing and tortuosity and 25% of cases shown complete obliteration.

CONCLUSION:

It is suggested that although the autonomic function, temperature discrimination or pain sensation might detect early sensory impairment, the testing methods are not yet reliable (van Brakel, 2000).Several studies proved that the sensibility testing using SW monofilaments is a sensitive test to detect the loss of peripheral nerve function and the moving 2 point discrimination is a sensitive test to screen the patients for nerve function impairment (NFI) provided the patient should understand the testing procedure well. It has been suggested that inability to recognize the 2 gms (hand) & 10 gms (feet) is an indication for loss of protective sensation. However it may require higher thresholds for people above 60 yrs and those who walk with barefoot.It has been strongly recommended that Moving 2 PD along with SW monofilament test or pin prick is the most sensitive and ideal method for screening the risk prone leprosy patients for NFI.Joint position sense and vibration sense is sensitive and are useful in detecting advance damage to the nerve trunk or chronic NFI. It has been found that the Biothesiometer is considered to be objectively reliable test, but it depend on a subjective response from the patient, hence should not be used as an alternative to more precise electrodiagnostic studies (such as nerve conduction studies).

Voluntary muscle testing, if possible, should complement sensory testing. Findings of several studies emphasize that ischaemia also plays a major role in production of trophic ulcers and other various lesions of leprosy like degeneration of nerves, osteolytic changes in bone and loss of function in limbs.Once neuropathy has been detected via physical examination and nerve function assessment, a definitive diagnosis will require the use of additional tests. These may include studies of nerve conduction velocity, electromyography, serology, haematology and cerebrospinal fluid, myelography, computed tomography and magnetic resonance imaging.Considerable variation in the classification and assessment of at risk status in the neuropathic foot still exists; therefore it is perhaps worthwhile to review the results in some detail. Since an accurate and reliable assessment of a patient's neuropathic status is important in determining the management, it is concluded that we should use the assessment methods that are well documented in the literature and furthermore should know how to interpret the results of such methods.

References:

1.            Bergtholdt, H. T. & Brand, P. W, Temperature assessment and plantar inflammation Leprosy Review 1976, 47, 3, p. 211-219.

2.            Birke, J. A. & Sims, D. S., Plantar sensory threshold in the ulcerative foot, Leprosy Review, 1986, 57, 3, p 261-267.

3.            Birke, J. A., Foto, J. G., Deepak, S. & Watson, J., Measurement of pressure walking in footwear used in leprosy, Leprosy Review, 1994, 65, 3, p 262-271.

4.            Debi, B. P., Mohanty, H. C., Tripathy, N., Tompe, D. B. & Sarangi, B. K. Arteriographic pattern of plantar ulcers in lepromatous leprosy--study of 20 cases Leprosy in India, 1980, 52, 3, p 429-432.

5.            Dorairaj, A., Reddy, R. & Jesudasan, K., An evaluation of the Semmes-Weinstein 6.10 monofilament as compared with 6 nylon in leprosy patients, Indian Journal of Leprosy, 1988, 60, 3, p 413-417.

6.            Faber, W. R., Reports from the Workshop on Neurologically Impaired Foot, Leprosy Review, 2003, 74, 1, p 84-85.

7.            Jain, G. L., Pasricha, J. S. & Guha, S. K. Minimum temperature felt as hot (MTH)--a new concept for grading the loss of temperature sensation in leprosy patients, International Journal of Leprosy & Other Mycobacterial Diseases, 1985, 53, 2, p 206-210.

8.            Koelewijn, L. F., Sensory testing in leprosy – Comparison of ballpoint pen and monofilaments, Leprosy Review, 2003, 74, 1, p 42-52.

9.            Oommen, P. K., Posterior tibial neurovascular decompression for restoration of plantar sweating and sensibility, Indian Journal of Leprosy, 1996, 68, 1, p 75-82.

10.        Patil, K. M., Sudhakar Babu, T., Oomen, P. K. & Srinivasan, H., Foot pressure measurement in leprosy and footwear design, Indian Journal of Leprosy, 1986, 58, 3, p 357 – 366.

11.        Patki, A. H., Infected trophic ulcers and tenderness of posterior tibial nerve in cured leprosy patients, International Journal of Leprosy & Other Mycobacterial Diseases, 1993, 61, 3, p 472-473.

12.        Stratford, C. J. & Owen, B. M., The effect of footwear on sensory testing in leprosy, Leprosy Review, 1994, 65, 1, p 58-65.

13.        van Brakel, W. H., Peripheral neuropathy in leprosy - The continuing challenge, Thesis, University of Utrecht, The Netherlands, 1994.

14.        van Brakel, W. H., Shute, J., Dixon, J. A. & Arzet, H., Evaluation of sensibility in leprosy--comparison of various clinical methods, Leprosy Review, 1994, 65, 2, p 106-121

15.        van Brakel, W. H., Detecting peripheral nerve damage in the field: our tools in 2000 and beyond, Indian Journal of Leprosy, 2000, 72, 1, p 47-64

16.        WHO, Expert Committee on Leprosy – Fourth Report, WHO Technical series Report, No.459, 1970, p 29.

SEMINAR ON FOOT PROBLEMS IN LEPROSY

Bombay Leprosy Project organized a Bank of Baroda sponsored Seminar titled ‘Neuropathic foot in Leprosy – A Review’ on 5^th May, 2003 at LTM Medical College, Sion, Mumbai – 400 022.Dr Satish Arolkar, an eminent Plastic Surgeon moderated the proceedings.Four Post graduate students from Physiotherapy Department of LTM Medical College & Hospital, Sion reviewed the literature and presented on various aspects of assessment and treatment of neuropathic foot problems in leprosy.Dr.R Ganapati, Director, BLP welcomed the gathering and stated that unfortunately the available technological advancement has still not reached the patients living in urban as well as rural terrains.Dr Lalit Varshney Ph D, Head, Product Development Group, ISOMED, BARC, Bombay presented on the use of ‘Hydrogel’ an agent for wound healing due to various causes including leprosy was the highlight of this Seminar. BLP proposes to undertake investigations with Hydrogel.Dr. Arolkar stressed that any intervention will not have the desired impact unless the underlying foot deficits are managed appropriately.He appealed to the medical fraternity to document their experience by way of publication so that it will have a wider reach. Dr V V Pai, Dy. Director of BLP proposed vote of thanks.

Section of the audience	Dr Varshney presenting on ‘Hydrogel’ dressings