Thermal threshold tester, a useful tool for detection of very early nerve damage--determination of normal values in a healthy population unexposed to Mycobacterium leprae and its application in the A9 study.

INTRODUCTION: In Ethiopia, a large percentage of leprosy patients present with established nerve damage. Present techniques for measuring nerve function impairment show no abnormality until 30% of nerve axons are destroyed. Nerve damage in leprosy occurs first in small diameter unmyelinated fibres, then in small myelinated fibres, and much later in large myelinated fibres. The Thermal Threshold Tester (TTT) was used to measure function in nerves carrying heat sensation (unmyelinated C fibres) and cold sensation (thinly myelinated Adelta fibres). PATIENTS: A school and community health survey, assessed 234 students and adults aged 10-75 years from Chencha Woreda, an area with low endemicity of leprosy. A group of students in Addis Ababa, exposed to leprosy, were also studied. RESULTS: The upper limits of normal were: wrist hot threshold (HT): 0.17 degrees C, wrist cold threshold (CT): 0.19 degrees C, foot HT: 0.17 degrees C and foot CT: 0.20 degrees C. Both the leprosy group and also controls in Addis Ababa showed significantly increased TTT values. CONCLUSION: The TTT detects nerve damage before clinical neuritis occurs and is a valuable tool for early diagnosis of leprosy or detecting clinical relapse of treated patients and for sequential and quantitative monitoring of small diameter nerve function in other neuropathies.

Peripheral nerves and nerve function in highland Ethiopians.

INTRODUCTION: In Ethiopia, where leprosy has been one of the commonest causes of peripheral nerve enlargement and dysfunction, nerve functions are assessed by a battery of "physical" tests. Voluntary Muscle Test (VMT) and Graded Sensory Skin Test (STG) are standard tests used for persons with leprosy. Normal values for nerve function tests (NFT) in Highland Ethiopians have not previously been determined, but have been taken from standard textbooks. In this study, normal values for NFT were determined by VMT, STG, 2-Point Discrimination Tests both static and moving, and Thermal Threshold Test. Physiological enlargement of right ulnar and radial-cutaneous nerves has been recognised by some leprologists, but we were unable to find written records in the available medical literature. MATERIALS: We assessed 236 students and adults aged 10-75 years from Chencha Woreda, an area with low endemicity of leprosy for 25-30 years. Two affected by leprosy were excluded from the analysis. RESULTS: NFT thresholds were affected variously by age, exercise and skin factors, domicile and exposure to organo-phosphates. Nerve size was affected by age, gender, exercise, skin fold thickness, body mass index. Exercise related physiological nerve enlargement has been documented. CONCLUSION: These data provide a usefull baseline for investigation of peripheral nerve function in highland Ethiopians.