Electrophysiological procedures in diagnosis of carpal tunnel syndrome

ABSTRACT

To evaluate some electrophysiological procedures adopted for the diagnosis of carpal tunnel syndrome [CTS] in Egyptian patients. The study was conducted on forty-one patients diagnosed as primary CTS according to the criteria proposed by the American Academy of Electrodiagnostic Medicine [AAEM, 1993]. The control group included thirty apparently healthy volunteers, of matching age and sex to the patients group. All patients and controls were subjected to history taking, thorough clinical examination and electrophysiological studies that included 1] Median and ulnar motor study, F-wave and axilllary F central latency, 2] Median and ulnar sensory study, 3] Median and ulnar mixed study and 4] Median lumbrical and ulnar interosseous study. Median motor conduction study revealed delayed distal latency, reduced CMAP amplitude and slowing in the forearm conduction velocity. Median sensory conduction studies revealed delayed sensory peak latency, slowed sensory conduction velocity of the median nerve in the distal segment and reduced SNAP amplitude. Motor and sensory nerve conduction studies of the ulnar nerve were all normal thus excluding the presence of peripheral neuropathy. Median nerve latency to the second lumbrical was prolonged and CMAP amplitude was reduced, also the difference between the median lumbrical and ulnar interosseous distal motor latency was prolonged whereas the ulnar to first palmar interosseous distal latency and CMAP amplitude were within normal The median mixed palm to wrist peak latency was prolonged and the difference between the median and ulnar mixed peak latencies was prolonged, the ulnar mixed palm to wrist peak latency and CMAP amplitude were within normal limits. The sensitivity and specificity for some tests were calculated and the results revealed that the highest sensitivity was for the median sensory peak latency to digit II versus the ulnar peak sensory latency to digit V 91.43%, followed by the median versus ulnar mixed palm to wrist peak latency 87.5%, the median lumbrical versus the ulnar interosseous distal latency 86.11%, median sensory peak latency to digit II 84.29% and lastly the median motor distal latency to the APB muscle 80.65%. The highest specificity was for the median versus ulnar mixed palm to wrist peak latency 100%, that is to say there were no false positive cases. So this test is highly specific, followed by the median sensory peak latency to digit II 95.0%, the median lumbrical versus the ulnar interosseous distal latency 92.5%, the median distal motor latency to the APB 92.5% and lastly the median sensory peak latency to digit II versus the ulnar peak sensory latency to digit V87.5%. The conventional motor and sensory conduction studies of the median nerve are sensitive and that calculating the difference between the median peak latency to digit II and the ulnar peak latency to digit V increases the diagnostic yield of the sensory study and increases the sensitivity of digit II sensory study. The median versus ulnar mixed palm to wrist peak latency is a very specific test that can be used as a screening test in cases of unilateral CTS. The median lumbrical versus ulnar interosseous distal latency is of high sensitivity and specificity