Introduction Ultrasound measurement of median nerve cross-sectional area (CSA) at the wrist has emerged as an accurate and useful complement to electrophysiology in the diagnosis of carpal tunnel syndrome (CTS).^{AANEM, 2012} A number of studies have also shown a positive correlation between median nerve CSA and electrodiagnostic severity. After noting absence of the expected nerve enlargement on ultrasound in some very elderly patients, we sought to correlate nerve ultrasound and electrodiagnostic findings in a very elderly population and to compare this with a population of younger patients.

Methods We undertook a retrospective review of electrophysiology and ultrasound data collected during routine clinical practice at our institution over a 13 month period. The correlation between electrodiagnostic severity and median nerve CSA at the wrist in patients aged 40–65 years (59 patients, 70 hands) was compared with a population of very elderly patients aged ≥80 years (33 patients, 40 hands). The sensitivity of nerve ultrasound for the detection of CTS was calculated for both groups.

Results In the 40–65 years age group, there was a strong positive correlation between electrodiagnostic severity and median nerve CSA (r=0.79, p<0.01). In patients aged over 80 years, there was no significant correlation between the two techniques (r=0.09, p=0.57). Compared to ‘gold standard’ electrophysiologic tests, nerve ultrasound sensitivity for the detection of CTS was 98% in the 40–65 years age group and 62% in the very elderly group.

Conclusion The absence of expected median nerve enlargement in very elderly patients with electrodiagnostic evidence of CTS may reflect a different pathophysiologic response to distal median nerve entrapment in advanced age. Our data also suggests that nerve CSA measurement alone may not be a reliable tool for the detection of CTS in the very elderly. Further studies of its diagnostic accuracy in very elderly patients are warranted.