August 26, 2013
In the most recent study published by Schmidt et al in Muscle & Nerve 2011, Vol 43, the diagnostic accuracy of the NC-Stat system in 50 patients with unilateral leg symptoms and 25 asymptomatic control subjects was studied. The research was done in a rigorous manor by experienced evaluators at the EMG lab of the Mayo clinic. The tests were all performed by technicians blinded to the findings of a standard electrodiagnostic evaluation, which was also performed. The NC-Stat resulted in very low specificity, thus a high false positive rate, in both symptomatic patients and in normal controls with an overall specificity for the NC-Stat of only 0.32.
In the same issue of Muscle & Nerve, John England and Gary Franklin concluded that because of the extremely low sensitivity the NC-Stat cannot be recommended as a diagnostic test for patients with lower extremity complaints. They quoted Armstrong et al from the J. of Occupational & Environmental Medicine, 2008, in the study on median and ulnar nerve conduction studies at the wrist that "NC-Stat is not designed to replace traditional methods of NCS".
From my experience in evaluating the upper extremity and seeing patients come into the office who have had NC-Stat studies, I am underwhelmed with the lack of utility of this tool especially because there is no way to really proof the work that is being done and signed off by a computer in Massachusetts to which all the data is sent. The NC-Stat is very limited with regard to interpretation of ulnar nerve dysfunction with the findings limited to those that can be obtained at the wrist which, for the most part, is a moot point. Most people who have ulnar nerve entrapment at the wrist also have concomitant median nerve entrapment. Carpal tunnel release surgery decompresses both nerves simultaneously. However, entrapment of the ulnar nerve at the elbow occurring in about 1 of 5 patients presenting with CTS goes undiagnosed. The NC-Stat relies on f-wave interpretation to suggest "further evaluation". This important diagnosis is hard to confirm even with conventional NCS with or without EMG. Clinical exam by a skilled physician is paramount.