The cholesterol levels in median nerve and post-mortem interval evaluation.

Cholesterol levels in the median nerve were studied at various post-mortem intervals (PMIs). Single median nerve samples were collected from the wrists of 36 subjects during forensic autopsies of subjects with known circumstances and times of death. Although the absolute values varied, increments in cholesterol concentration were recorded. Subsequently, 16 subjects who did not suffer of any neurological and/or metabolic diseases with known times and circumstances of death were enrolled. For each enrolled subject, two samples were collected from the wrist at an interval of approximately two hours (t1 and t2). The obtained results revealed a gradual increase in cholesterol level with increasing time since death. The cholesterol concentration data obtained for each subject at t1 and t2 were correlated with the time since death, a linear interpolation was applied, and the PMI was back-calculated. Similar trends were obtained for the samples collected at similar PMIs; thus, three groups were considered: PMI<48h, 4878h. Good correlation coefficients were obtained, especially for the first group (R(2)=0.9362) for which the PMI could be calculated with an error that ranged from -4 to 5.9h. Although it requires further confirmation via analyses of larger numbers of samples, the method proposed here can currently be applied to PMI determinations.

An ultrastructural and biochemical analysis of collagen in rat peripheral nerves: the relationship between fibril diameter and mechanical properties.

Mechanical features are distributed heterogeneously within nerve tissue, with compliance increased at articulations. This study explored whether differences in stiffness between joint regions (JRs) and non-joint regions (NJRs) of rat median and sciatic nerves were related to localised variation in collagen content or fibril diameter. There was no significant difference in the amount of collagen detected by biochemical assay in JRs and NJRs of either nerve. Ultrastructural analysis showed collagen fibril diameter ranges of 20-80 nm in the endoneurium and perineurium and 30-130 nm in the epineurium. In the median nerve, but not the sciatic nerve, there were significantly smaller fibrils in JRs compared to NJRs. This corresponded to a greater number density of fibrils in JRs compared to NJRs in the epineurium and endoneurium of the median nerve. We report the presence therefore of a population of thinner collagen fibrils in the JR of the median nerve that corresponds to the location of increased compliance in this tissue, suggesting that localised variation in collagen fibril diameter contributes to the longitudinal heterogeneity of tensile properties in this nerve.

Performance of a high-repetition, high-force task induces carpal tunnel syndrome in rats.

STUDY DESIGN: A randomized controlled prospective experimental study with some repeated measures. OBJECTIVES: To characterize behavioral, sensory, motor, and nerve conduction decrements, and histological changes in the median nerve in rats trained to perform a high-force repetitive task. BACKGROUND: Understanding of work-related carpal tunnel syndrome is hampered by the lack of experimental studies of the causes and mechanisms of nerve compression induced by repetitive motion. Most animal models of nerve compression have not employed voluntary repetitive motion as the stimulus for pathophysiological changes. METHODS AND MEASURES: Thirty Sprague-Dawley rats served as controls for 1 or more studies. Ten rats were trained to pull on a bar with 60% maximum force 4 times per minute, 2 h/d, 3 d/wk for 12 weeks. Motor behavior and limb withdrawal threshold force were characterized weekly. Grip strength and median nerve conduction velocity were measured after 12 weeks. Median nerves were examined immunohistochemically for ED1-positive macrophages, collagen, and connective tissue growth factor. RESULTS: Reach rate and duration of task performance declined over 12 weeks. Grip strength and nerve conduction velocity were significantly lower after 12 weeks than in controls. Limb withdrawal threshold increased between weeks 6 and 12. Median nerves at the level of the wrist showed increases in macrophages, collagen, and connective-tissue growth-factor-positive cells. These effects were seen in both the reach and nonreach limbs. CONCLUSIONS: This animal model exhibits all the features of human carpal tunnel syndrome, including impaired sensation, motor weakness, and decreased median nerve conduction velocity. It establishes a causal relationship between performance of a repetitive task and development of carpal tunnel syndrome.

Bilateral carpal tunnel syndrome secondary to tophaceous compression of the median nerves.

A 65-year-old man with long-term gouty arthritis developed bilateral carpal tunnel syndrome. At surgery a chalky substance, which showed negative birefringence on polarized microscopy, was found infiltrating around the intensely inflamed transverse carpal ligaments. In differential diagnosis of carpal tunnel syndrome, tophaceous compression over the median nerve should be taken into consideration.