Optimizing the number of tests for carpal tunnel syndrome.

The combined sensory index (CSI), the sum of three latency differences, median-ulnar across the palm (palmdiff), median-ulnar to the ring finger (ringdiff), and median-radial to the thumb (thumbdiff), has higher sensitivity and reliability for carpal tunnel syndrome than individual tests. The objective in this study was to develop an approach that minimizes testing but maximizes accuracy. We retrospectively studied 300 hands. There were endpoints for individual tests that confidently predicted the CSI; for ranges between these endpoints, further testing was required. These ranges were: palmdiff 0-0.3 ms; ringdiff 0.1-0.4 ms; and thumbdiff 0.2-0.7 ms. One may use a strategy in which more tests are performed when results are in these ranges. This approach can allow accurate diagnosis with fewer tests when values are extreme, yet uses the greater diagnostic power of more tests when values are midrange.

Somatosensory potentials, CSF creatine kinase BB activity, and awakening after cardiac arrest.

OBJECTIVE: To examine the utility of somatosensory evoked potential (SEP) peaks and CSF creatine kinase BB isoenzyme activity (CKBB) in predicting nonawakening from coma due to cardiac arrest. BACKGROUND: Accurate predictors of neurologic outcome in patients comatose after cardiac arrest are needed to improve medical decision making. METHODS: A total of 72 comatose patients had bilateral median SEPs, and of these, 52 had CSF and CKBB. Awakening was defined as following commands or having comprehensible speech. Both short (N1) and long (N3) latency SEP peaks were analyzed. Nonparametric analyses were used. RESULTS: For patients who had both tests, CKBB > or = 205 U/L predicted nonawakening with a sensitivity of 49% and a specificity of 100%. Bilateral absence of the N1 peak predicted nonawakening with a sensitivity of 53% and a specificity of 100%. Using CKBB > or = 205 U/L, bilaterally absent SEP N1 peaks, or both predicted nonawakening with a sensitivity of 69% and a specificity of 100%. Using CKBB > or = 205 U/L, bilaterally absent N1 peaks, bilateral N3 > or = 176 msec or absent, or some combination predicted nonawakening with a sensitivity of 78% and a specificity of 100%. CONCLUSION: The combination of an absent N1 peak and elevated CKBB performs better than either alone in predicting nonawakening after cardiac arrest. Prolonged or absent N3 latency may increase sensitivity. These results should be interpreted with caution given the small number of patients and the possibility of a self-fulfilling prophecy.

Strategies for analyzing nerve conduction data: superiority of a summary index over single tests.

We compared three strategies for diagnosing carpal tunnel syndrome: using a single test; requiring one, two, or three of three tests to be abnormal; or utilizing a single summary variable incorporating data from three tests. Sixty-five hands of subjects without clinical carpal tunnel syndrome (CTS) were compared with 66 hands with clinical CTS. Three latency differences were measured: median-ulnar (8 cm) midpalmar orthodromic (palmdiff); median-ulnar ring finger (14 cm) antidromic (ringdiff); and median-radial thumb (10 cm) antidromic (thumbdiff). The combined sensory index (CSI) was the sum of these three differences. Sensitivity for the tests was palmdiff 69.7%, ringdiff 74.2%, thumbdiff 75.8%, and CSI 83.1%. Specificity was 95.4-96.9%. Requiring one, two, or three of three tests to be abnormal yielded sensitivities of 84.8%, 74.2%, or 56.1%, respectively, but specificities of 92.3%, 98.5%, and 100%, respectively. We conclude that a combined index improves diagnostic classification over use of single test results.