‘Thumb localizing test’ for detecting a lesion in the posterior column–medial lemniscal system

A recent paper by Hirayama and colleagues [1] reported was between the TLT and tests of joint position sense, with that the ‘thumb localizing test’ (TLT) was useful for k50.31. Any value of k,0.40 indicates poor agreement detecting a lesion in the posterior column–medial lemniscbeyond chance. Thus, the inter-test agreement between the al system. This easily performed bedside test uses an TLT and other standard clinical sensory tests was uniforminteresting approach to detect perceptual deficits of a limb ly poor for the tests studied, including those generally since it relies on a motor task of the opposite limb. considered tests of the posterior column–medial lemniscal However, the conclusion that it specifically assesses the system. posterior column–medial lemniscal system needs further Further work needs to be done to establish the spesupport before it can be accepted. cificity of this test for any particular sensory pathway. It The authors studied a large series of patients with would be of particular interest to see how results of this sensory deficits, but more than half had cerebral, cervical test agree with those of line direction (‘direction of root, or peripheral nerve lesions — all of which are likely scratch’) tests, vibration perception thresholds, and somto result in mixed deficits. The authors compared results atosensory evoked potentials. Optimally, such comparisons between the TLT and other clinical sensory tests of joint would be based on patients with and without focal lesions position and movement, tactile cutaneous localization, of specific sensory systems in the spinal cord and braintouch, vibration, pain, and temperature using a ‘chi-square stem. test.’ They reported ‘strong correlations’ between TLT and either joint position or tactile cutaneous localization tests, as indicated by highly statistically significant P-values. However, the P-values do not appear to be based on the Table 1 appropriate McNemar’s statistic for paired comparisons Comparison test P P k 95% CI P-values o e (and further do not match a chi-square test for unpaired Pain 0.56 0.50 0.12 0.023, 0.212 0.015 comparisons). More importantly, a small and highly sigTemperature 0.59 0.56 0.07 20.024, 0.168 0.142 nificant P-value does not measure the strength of a Touch 0.65 0.55 0.22 0.127, 0.322 ,0.0001 relationship or the degree of agreement between the tests. Vibration 0.62 0.55 0.17 0.074, 0.270 0.001 We calculated kappa statistics (k) [2,3] for the data (in JPM 0.72 0.60 0.31 0.223, 0.387 ,0.0001 TCL 0.68 0.61 0.17 0.102, 0.245 ,0.0001 the authors’ Table 2) to assess the agreement beyond chance between the TLT and other standard clinical Notes: JPM5joint position and movement; TCL5tactile cutaneous sensory tests (see Table 1 below). The strongest agreement localization; P 5overall proportion of agreement; P 5overall proportion o e of chance-expected agreement; k5index of agreement beyond chance, where k50 indicates no agreement beyond chance, 0,k,0.40 indicates poor agreement beyond chance, and k51 indicates perfect agreement. *Corresponding author. Tel.: 11-608-3272-1778; fax: 11-608-3272P-values are given for tests of the hypothesis that the ratings are 1654. independent (i.e. k50), against the alternative that agreement is better E-mail address: douglas.lansaka@med.va.gov (D.J. Lanska) than chance.