We should not use a modifier to describe the severity of carpal tunnel syndrome

Many electromyographers prefer to use a severity modifier, such as mild, moderate, or severe, when they give an electrodiagnostic impression of carpal tunnel syndrome (CTS). For instance, many will report a diagnosis of “moderately severe carpal tunnel syndrome” in the impression on their electrodiagnostic report. I do not believe we should do this. We can do better. We can and should give more useful and valid information in our reports. What are the reasons electrodiagnostic consultants feel they should include a description of severity in the impression? I have heard several reasons brought up during national meetings, but most commonly I hear that using a severity term will guide the referring physician in making an appropriate treatment decision. Some report that use of a severity modifier provides a comparison of CTS severity in the specific patient studied against others who have CTS. Yet others report that the use of a severity term allows comparison over time. These are all laudable reasons. Unfortunately, we do not have the required information to support the use of a modifier term in these ways. Why not? First, CTS is a syndrome. A syndrome consists of an aggregation of symptoms and signs associated with a morbid process, which together constitute the picture of the disease. This is different than what we measure in electrodiagnostic testing. There is, unfortunately, a poor correlation between clinical symptoms and electrodiagnostic findings, such as prolongation of latency or reduction in amplitudes of compound muscle action potential (CMAP), and/or sensory action potentials in patients with CTS. Symptoms are not elicited by slowing of conduction. They are instead elicited by ectopic excitation of the compressed nerve, by conduction block and loss of axons, by central sensitization, and by disinhibition, none of which are measured well by electrodiagnostic testing. There are some individuals who have the syndrome but have no slowing of latency or reduction in SNAP or CMAP amplitudes. On the other hand (so to speak), some patients have excellent relief of symptoms after successful surgery but have persistently prolonged latencies—a result of altered myelin morphology after demyelination and subsequent remyelination. A second problem with using a severity modifier in the diagnosis of CTS is that the schemes devised for doing this are, to some degree, arbitrary and inconsistent. Most schemes use the degree of slowing and presence or absence of motor and sensory action potentials, but these models raise more questions than they answer. What other criterion was used to give the scheme either construct or predictive validity? (i.e., what was the “gold standard”? ). How were the cut-offs chosen? Which and how many nerve conduction studies should be performed to assess severity? What happens if some results fit 1 severity category (e.g., mild) and other results fit another severity (e.g., moderate)—which is chosen? Of the several systems described, which should be used? Independent of which system is used for assigning severity, it is unclear that the electrodiagnostic severity should be used to guide treatment. Do we have any evidence that patients with mild CTS should have non-surgical treatment, and should those with severe CTS should be rushed to the operative suite? In reality, as with any disease, the treating physician will take many factors into account in recommending treatment including: duration and severity of symptoms; functional impact of the disease; type of occupation; time off work; other medical conditions or comorbidities; and many others. It may not be best to defer surgery for someone with severe symptoms only because the electromyography (EMG) results were “mild CTS,” just as it may not be optimal to recommend surgery to someone with “severe” CTS if there is little functional impact from the disease. To complicate treatment decisions further, the association between severity of nerve conduction abnormalities and outcomes after surgery is nonThis article was approved and edited by committees of the AANEM, and it did not undergo further peer review by Muscle & Nerve.