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Sensory testing in patients with chronic venous leg ulcers

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Studies have shown the presence of peripheral sensory neuropathy in patients with severe chronic venous insufficiency. (Reinhardt et al, 2000; Padberg et al, 1999; Shami et al, 1993) This could, therefore, be considered a cofactor in the pathogenesis of venous ulceration. Altered nervous control of the skin microcirculation may cause:

Abstract

 

VOL: 99, ISSUE: 31, PAGE NO: 55

Minerva Arseculeratne, MBBS, MPhil, Visiting Research Fellow

George Cherry, DPhil, Director; Oxford Wound Healing Institute, Churchill Hospital, Oxford, UK

 

Studies have shown the presence of peripheral sensory neuropathy in patients with severe chronic venous insufficiency. (Reinhardt et al, 2000; Padberg et al, 1999; Shami et al, 1993) This could, therefore, be considered a cofactor in the pathogenesis of venous ulceration. Altered nervous control of the skin microcirculation may cause: - Abnormalities of the vasomotor system; - Impairment of the venoarteriolar reflex; - Increased skin blood flow in lipodermatosclerotic skin (induration resulting from fibrosis of subcutaneous fat) of patients with chronic venous insufficiency (Shami et al, 1993). Sensory impairment probably contributes to the deterioration that occurs in local tissue following a minor trauma in patients with chronic venous insufficiency (Padberg et al, 1999). The aim of this study was objectively to ascertain the presence of a sensory neuropathy in the feet of patients with chronic venous insufficiency, using a 10g Owen Mumford monofilament. Method
We randomly selected 15 patients with venous leg ulcers attending the leg ulcer clinic at the Churchill Hospital, Oxford. Informed consent was obtained, and medical histories and Doppler assessment of the pedal pulses were undertaken in order to exclude arterial disease in the legs. We used a 10g Owen Mumford monofilament for objective sensory testing of the feet. This was done in a quiet environment where the patients could relax. We explained to them what we anticipated from the testing. The monofilament was applied perpendicularly to the skin’s surface and then sufficient pressure was applied so that the filament buckled (Fig 1). The skin sites chosen are depicted in the diagram of the plantar and dorsal aspects of the foot (Fig 2). These 10 sites were tested in random order. The contact time was kept to within 1.5 seconds. The patients were asked to close their eyes and report any sensation when the monofilament was applied to the skin. Patients were categorised as having normal pressure perception if they were able to feel more than eight of the 10 sites tested (Paisley et al, 2002; Holewski et al, 1988). Results
- Seven of the 15 patients (47 per cent) had normal pressure sensation in the foot bearing the ulcer (Table 1). - The remaining eight (53 per cent) exhibited some degree of loss of sensation in the foot bearing the ulcer (Table 1). Of these eight, three had more than 50 per cent loss of sensation. Five patients had callus formation at some of the test sites on the soles of their feet. These sites were insensitive to the pressure applied. Four of these five patients had normal pressure sensation despite having callosities on the soles of their feet. Sites two and five were the sites most frequently found to be non-sensitive to the monofilament. No correlation was found between a patient’s age and the degree of neuropathy. There was a positive correlation between the ulcer duration and the degree of neuropathy. Patients’ individual blood glucose levels were all within the normal range - random blood sugar: <11.1mmol/l; fasting blood sugar: <7.0mmol/l - as defined by the World Health Organization. Discussion and limitations
This simple test was well tolerated by patients. Testing took less than five minutes for each patient. Forty-seven per cent of the patients exhibited normal pressure sensation in the foot of the leg bearing the ulcer; 53 per cent showed some degree of loss of sensation. Patients with callosities on the soles of their feet may have benefited from a chiropodist attending to the thickened skin if the loss of sensation was due to callus formation and not to any sensory impairment. Twenty per cent of patients demonstrated more than a 50 per cent loss of sensation. These patients did not give a history of a chronic high alcohol intake or exposure to neurotoxic agents, including medication. Since there was no correlation between age and the degree of neuropathy, age-related neuropathy was ruled out. A positive correlation between ulcer duration and degree of neuropathy indicates the longer the duration of an ulcer, the greater the degree of neuropathy. Chronic venous insufficiency is characterised by a congenital or acquired abnormal functioning of the venous system, causing microvascular hypertension. Changes in the capillaries include elongation and dilatation, endothelial damage and enlarged interendothelial spaces. Intracapillary microthrombosis results in tissue ischaemia and necrosis. Clinically, this syndrome is characterised by venous dilatation, changes in skin pigmentation, oedema as well as ulceration (Leu et al, 1995). Patients with chronic venous insufficiency and controls have been examined for neuropathy by testing the thresholds to warming, cooling and vibration sense. Shami et al (1993) found a significantly raised threshold to warming and vibration in a group of people with chronic venous insufficiency when compared with a control group, although the thresholds to cooling in the two groups were not statistically different. Studies have also revealed, in addition to light touch or pinprick, vibration sense and deep tendon reflexes are sometimes significantly worse in patients with chronic venous insufficiency (Padberg et al, 1999). Jeng et al (2000) found that the inability to feel the pressure from a 10g Semmes-Weinstein monofilament represents a sensory threshold that is more than 50 times greater than normal. The inability to sense the pressure applied by this instrument amounts to approximately 98 per cent of the sensory ability being lost. The accuracy of monofilaments to produce a buckling force of 10g varies among manufacturers. Booth and Young (2000) showed that the Owen Mumford monofilaments were one of the most accurate, with 100 per cent buckling force within [s6]1g of 10g. Some studies suggest that nerve damage in patients with chronic venous insufficiency may be due to venous microangiopathy-related ischaemia and elevated endoneurial pressure, which may play a part in the pathogenesis of neuropathies (Junger et al, 2000). Conclusion and recommendations (Box 1)
From this preliminary study we would recommend using the 10g Owen Mumford monofilament as a screening test for sensory neuropathy in patients in the community with chronic venous insufficiency in order to detect early loss of sensation, thereby preventing deterioration of minor trauma into chronic venous leg ulceration. - A full version of this article can be found in the Journal of Wound Care. Arseculeratne, M., Cherry, G. (2003) Sensory testing in patients with chronic venous leg ulcers using a 10g Owen Mumford monofilament. Journal of Wound Care; 12, 6, 215-217. Or visit www.journalofwoundcare.com

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