The reliability and validity of the locognosia test after injuries to peripheral nerves in the hand.

Locognosia, the ability to localise touch, is one aspect of tactile spatial discrimination which relies on the integrity of peripheral end-organs as well as the somatosensory representation of the surface of the body in the brain. The test presented here is a standardised assessment which uses a protocol for testing locognosia in the zones of the hand supplied by the median and/or ulnar nerves. The test-retest reliability and discriminant validity were investigated in 39 patients with injuries to the median or ulnar nerve. Intraclass correlation coefficients were used to calculate the test-retest reliability. Discriminant validity was assessed by comparing the injured with the unaffected hand. Excellent test-retest reliability was demonstrated for the injuries to the median (intraclass correlation coefficient 0.924, 95% confidence interval 0.848 to 1.00) and the ulnar nerves (intraclass correlation coefficient 0.859, 95% confidence interval 0.693 to 1.00). The magnitude of the difference in scores between affected and unaffected hands showed good discriminant validity. For injuries to the median nerve the mean difference was 11.1 points (1 to 33; SD 7.4), which was statistically significant (p < 0.0001, paired t-test) and for those of the ulnar nerve it was 4.75 points (1 to 13.5; SD 3.16), which was also statistically significant (paired t-test, p < 0.0001). The locognosia test has excellent test-retest reliability, is a valid test of tactile spatial discrimination and should be included in the evaluation of outcome after injury to peripheral nerves.