Objective: The study assessed the influence of the length of the across elb
ow (AE) segment of the ulnar nerve on the true and false positive rates of
velocity measurements: of the AE segment. Using a short AE length will incr
ease effects of the measurement error (ME), and using a long distance will
'dilute' the slowing due to the focal lesion; it is not known which length
is optimal to detect focal slowing.
Methods: A simulation was performed to assess diagnostic yield for AE lengt
hs of 50, 100 and 150 mm, taking into account ME, variation in true velocit
y, and severity of the lesion. ME of latencies and distances were first det
ermined in a healthy subject.
Results: ME proved lower than in a published study. Diagnostic yield was co
nsistently better for an AE length of 50 mm than for 100 or 150 mm. The opt
imum length is therefore near 50 mm. Yield increased with severity of the l
esion, smaller ME, and when interindividual variation in true velocity was
small. Judging AE on its own had a slightly better yield than comparing AE
velocity to forearm velocity, except for populations with a larger than nor
mal spread in true conduction variability.
Conclusions: The best balance between effects of ME and 'dilution' to detec
t focal nerve slowing is obtained at nerve lengths of about 50 mm. The need
to incorporate all possible compression sites necessitates the use of a su
boptimal length of about 80 mm. (C) 2001 Elsevier Science Ireland Ltd. All
rights reserved.